Browsing by Department "Animal Science"

The influence of feeds containing varying dietary cation-anion differences (DCADs) with and without supplements of 25-hydroxyvitamin D (25(OH)D) on urine pH and excretion of macro minerals was determined in fistulated crossbred steers (mean live weight 315 ± 45 kg). A basal forage diet comprising lucerne hay and wheat chaff was used, to which varying quantities of MgCl2 or K₂CO₃ were added to achieve four levels of DCAD: -300, 50, 150 or 250 mEq/kg dry matter (DM). Steers were allocated to one of six treatments, one treatment for each diet and a further treatment for both the 50 and 150 mEq/kg DCAD diets, which were supplemented with 25(OH)D at a rate of 3 mg/steer per day. Urine pH from steers offered the diets comprising DCADs of 50, 150 and 250 mEq/kg ranging from 8.3 to 8.8. In treatments not containing 25(OH)D with DCADs of 50 to 250 mEq/kg, there were no significant differences in urine pH or Ca excretion. However, steers offered the diet with a DCAD of 2300 mEq/kg DM produced urine with a significantly lower pH (6.5 to 7.5). Daily output of Ca in urine was also significantly higher from steers given this diet. Supplementation with 25(OH)D significantly increased urinary Ca excretion from steers offered diets of DCADs 50 and 150 mEq/kg DM. Estimates of daily urinary Ca excretion, calculated using the ratio of creatinine to Ca in 'spot' urine samples, were less variable than those based on total collection (residual mean square of 0.54 and 0.63, respectively).

The growth-promoting effect of sub-theraputic levels of antibiotics in animal feed was first described in the late 1940s when chickens fed fermentation waste from an antibiotic (tetracycline) plant grew more rapidly than controls (Dibner and Richards, 2005). Since 1950, a wide range of in-feed antibiotics (IFAs) has been available to the broiler industry. In the 1950s, the bulk of the antibiotic agents from the pharmaceutical industry were derived from 'Streptomyces spp'. Many antibiotic substances have been shown to improve FCR and animal growth and reduce morbidity and mortality due to clinical arid subclinical diseases (Rosen, 1995). In a holo-analysis of several studies, Rosen (1995) reported that in 72 % of 12,153 studies from 55 countries, conducted in the preceding 50 years, antibiotics improved growth and feed efficiency by 2-3 %. Ewing and Cole (1994) suggested that average growth improvement of IFA is between 4-8 % and feed utilization can be improved by 2-5 %.

This chapter addresses diseases and syndromes which have been shown, or are reported, to have adverse effects on egg production and quality. However, any disease of poultry can adversely affect egg production and quality indirectly, by affecting the health of the bird. The main topics are the effect on egg production and quality of bacteria ('Salmonella', 'Mycoplasma', 'Escherichia coli', infectious coryza, 'Ornithobacterium', 'Gallibacterium', spirochaetosis), viruses (infectious bronchitis virus, egg drop syndrome, swollen head syndrome, avian encephalomyelitis, influenza, Newcastle disease, laryngotracheitis), syndromes (fatty liver haemorrhagic syndrome, cage layer osteoporosis) and toxic agents. A short section on clinical perspectives reports on information obtained from practising poultry veterinarians as such observations can provide valuable starting points for future research.

Microarrays are currently the de facto tool for simultaneously studying expression profiles across thousands of genes. For research purposes, RNAseq will probably supersede them over the next few years as the global expression-profiling tool of choice (Ledford 2008). Currently RNAseq costs are still non-competitive, but they are dropping rapidly. The costs of mainstream array technologies are also steadily coming down, which will allow them to be more widely used as a diagnostic tool. Within this niche they are not likely to be replaced in the near future. For many livestock species, commercial arrays are available and frequently there is more than one platform/supplier. The choice of platform is important in terms of robustness and its ability to address the experimental questions. The three most commonly used bovine gene expression platforms used for global transcription profiling studies are the 'Affymetrix GeneChip Bovine Genome Array', the 'Agilent Bovine Gene Expression Microarray' and the 'Bovine Oligo Microarray Consortium (BOMC) 24K array'. The objective of this work is to summarize and compare these platforms, and propose some suggestions to assist researchers to make a decision about which one to use in their own projects.

Australian sheep grazing environments are currently classified into 3 very broad zones (High Rainfall, Wheat/Sheep and Pastoral) that do not differentiate sheep grazing environments to a level allowing sheep producers to assess the impact grazing environments may have on sire progeny performance. If a genotype by environment interaction (GEI) is expressed more as environments diverge then a finer classification of environments may help breeders when selecting stud rams. A sheep grazing environment classification system has been developed in this study using readily obtainable monthly Normalised Difference Vegetation Index (NDVI), from satellite data, and monthly maximum temperature for a 10 year period. Cluster analysis was used on the NVDI and temperature data to create 25 sheep grazing environment classes (SGEclass) around Australia. Two-way analysis of variance revealed a significant interaction between sire progeny performance and SGEclass for hogget weight, fibre diameter and greasy fleece weight. Further ASReml analysis of Merino data from Sheep Genetics illustrated that sire by SGEclass explained similar amounts of variation as sire by flock. Recording the geographic location of the flock would improve the ability to account for environmental differences between flocks.

Stocking rate is often the most important and manageable factor influencing the profitability and environmental sustainability of pastoral properties. Methods for determining carrying capacity, and therefore stocking rate, include subjective approaches based on land manager experience, long-term 'benchmark' stocking rates and techniques using computer-aided predictions of pasture growth. This paper presents a new approach for objectively calculating short-term livestock carrying capacities of pastoral properties by integrating remotely sensed ground cover assessments as a proxy for land condition. The study region was three commercial pastoral properties in the north Australian pastoral region (above 26°S). Two properties were situated in the Victoria River District of the Northern Territory and a third in the Kimberley region of Western Australia. Annual pasture growth was estimated using GRASP, a deterministic, point-based, native pasture model developed for semiarid and tropical grasslands, which was calibrated for the different land types in the study region. Carrying capacity estimates were further refined by investigating trends in landscape cover change between years using data from satellite imagery assessment. These tools have been shown to be useful for inferring land condition and pasture growth within these regions of northern Australia but had not been integrated before this study. This study developed an approach for inferring rangeland pasture condition and applying it to refine short-term carrying capacities, thus aiding decision making. The approach developed in this study is considered to be more applicable for commercial land management than currently available methods for determining carrying capacities on pastoral properties in northern Australia.

An experiment was conducted to develop and optimize a chicken bioassay to detect the presence of infective viral pathogens in poultry litter from a variety of sources. The experiment also aimed to determine the effect of type of chickens and age of exposure to litter on the level of viral infectivity. The bioassay detected chicken anaemia virus, infectious bursal disease virus and fowl adenovirus from chicken litters. SPF chickens showed higher sensitivity than commercial broiler chickens without any effect of age of exposure, however, the assay was more sensitive in broiler chickens when exposed at day 8. We conclude that the bioassay based on exposure of day-old SPF chickens is a viable assay of viral infectivity of poultry litter.

Objective: To develop a chicken bioassay to detect infective viral pathogens in poultry litter and to determine the effects of type of chicken and age of exposure, as well as the effect of simulated litter transportation, on the level of viral infectivity detected. Design: A 5 x 2 x 2 factorial design, plus negative controls. Five chicken litters, including two with deliberate contamination (one transported and one not), two chicken types (specific-pathogen-free (SPF) Leghorns and Cobb broilers) and two ages at initial exposure (days 1 and 8). Two replicates of each treatment combination. Methods: The 10 chickens in each of 22 isolators were either exposed (20 isolators) or not (2 isolators) to 8 L of previously used or deliberately contaminated poultry litter in two deep scratch trays. At day 35 post-exposure, sera were assayed for antibodies against chicken anaemia virus (CAV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), Newcastle disease virus (NDV) and fowl adenovirus (FAV). Spleen samples were tested for Marek's disease virus (MDV) using real-time polymerase chain reaction. Results: The bioassay detected CAV, IBDV and FAV, but not NDV, IBV or MDV, in chickens exposed to infected litters. Infection in SPF chickens was detected with greater sensitivity than in the broiler chickens. Sensitivity increased with age at exposure in broiler but not SPF chickens. Simulated transportation for 24 h had little effect on pathogen detection. Conclusion: A bioassay based on the exposure of day-old SPF chickens to poultry litter and measurement of seroconversion at day 35 post-exposure is a useful semi-quantitative assay for viral infectivity in poultry litter, with overnight transportation of litter having little effect on the level of viral infectivity detected. This bioassay has applications in research on litter treatment protocols.

We investigated the development of standardised methods of extraction and quantitation of viral nucleic acids from broiler litter. To detect and quantify virus we used fully quantitative Taqman® qPCR assays with plasmid-based standard curves to quantify Marek's disease virus (MDV, dsDNA), infectious laryngotracheitis virus (ILTV, dsDNA), Fowl adenovirus (FadV, dsDNA), chicken anaemia virus (CAV, ssDNA) and infectious bursal disease virus (IBDV, dsRNA). A series of experiments examined the effects of litter washing, blending, bead beating, and removal of inhibitors using polyvinylpolypyrrolidone (PVPP). To evaluate the qPCR assays and the DNA extraction techniques we monitored the recovery of fixed amounts of virus added to litter samples. The three litter types used were hardwood shavings, softwood (pine) shavings and rice hulls. Hardwood shavings were shown to contain high levels of PCR inhibitors but these could be neutralised by PVPP. Detectable virus recovery was good for IBDV and CAV, but low for the dsDNA viruses ILTV and MDV. The third dsDNA virus, FAdv, was unable to be detected. The four detectable viruses were detectable in all fractions of material (retentate after filtration, and in both the pellet and supernatant fractions following centrifugation of the filtrate) with highest concentrations in the pellet. The results indicate that a method based on washing samples with buffer containing 0.15% Tween-80 followed by bead beating and PVPP treatment would enable detection of most DNA and RNA viruses from litter with the greatest concentration of virus found in the pellet fraction after centrifugation. Work is ongoing to resolve the low recovery rate of dsDNA viruses and to simplify the litter processing and DNA extraction further.

The study of mammalian development has historically relied on morphological observations and the evaluation of developing offspring in utero. This painstaking work has resulted in detailed and meticulous descriptions of the events and structures that arise during this elegantly orchestrated process (Patten, 1948). The developmental genetics of the pig, as with many other mammals, was hindered for a long time owing to the tremendous complexity of development and the lack of appropriate methods. However, recent advances in molecular techniques and gene expression profiling have resulted in the generation of a vast amount of data concerning the genetics of mammalian development. A great deal of this work has been carried out in the mouse, but there are increasing amounts of information on the embryology and genetics of development in economically important agricultural species such as the pig. Drawing on this information, this chapter is intended to provide an overview of the current understanding of mammalian development as it relates to pigs.

About 2/3 of introns are inserted between G and G/A, which has previously been explained by codon usage frequencies existing during the period of intron insertions. However, less is known about the evolution of exonic splicing sites. Exonic nucleotides that frame introns are involved in both protein coding and splicing. While a compromise between protein coding and splicing constraints is achieved differently in each intron phase, AG|G is the most common site in all phases comprising about one quarter of all such sites. There is also a great variety of other splicing sites. Here we examine evolutionary changes in exonic nucleotides located at positions −2 −1|+1 which occurred after the beginning of eutherian radiation using comparisons of orthologous splicing sites from five mammalian species. AG|G accumulated fewer substitutions and was more conservative than less frequent exonic splicing sites. Such trend could potentially increase frequencies of AG|G during mammalian evolution and cause a decline of less common sites which had higher substitution rates. However, there is a limit to this process determined by the dynamic equilibrium of substitution rates and the frequencies of different splicing sites. It seems that this equilibrium was already achieved at the time of eutherian radiation and a moderate increase in AG|G frequency was observed only in the human genome.

Wheat is a common raw material in Australian broiler diets because of its high starch and protein content. However, the main concern with wheat is the presence of soluble non starch polysaccharides (NSPs), especially arabinoxylans. Arabinoxylans may account for up to 61 g/kg of wheat dry matter (Choct and Annison, 1990). These NSPs are difficult to digest and may cause digesta to become viscous thereby reducing nutrient digestion and absorption. Many NSP degrading enzyme products are commercially available and are used in the poultry feed industry. This study was undertaken to compare the effect of different enzymes preparations on in vitro viscosity of different wheat varieties.

In the first of a two-phased study, changes in rumen pH and concentrations of VFA were evaluated on diets based on pasture straw (negative control) or straw supplemented with alfalfa (Alfalfa diet), pods of 'Acacia sieberiana' (Sieberiana diet), 'Acacia nilotica' (Nilotica diet) or 'Leucaena leucocephala' (Leucaena diet) for South African Merino rams. In the second phase, the effects of the same diets on the degradation of extracted straw in nylon bags and activities of microbial enzymes were investigated. The pH and total concentration of VFAs in rumen fluid ranged from 6.2 to 6.5 and 30–53 mmol l⁻¹, while degradation of DM and NDF varied from 126 to 269g kg⁻¹ DM and 233–309 g kg⁻¹ NDF, respectively, among diets. Variations in pH were not significant (P > 0.05), but diet influenced (P < 0.01) the concentration of VFAs, degradation of DM and cell wall constituents as well as enzyme activities of proteolytic and fibrolytic microorganisms. The results showed that the differences between the alfalfa and pod diets might have been due mainly to the presence of tannins in the pods. These compounds limit the growth and/or activity of ruminal microorganisms. However, a limitation in the supply of energy imposed by the pod diets may have reduced the efficiency of N capture by microorganisms leading to a depression in microbial activity. The tested legume pods could be used in limited quantities to supplement low-quality forage. The pods may need to be detoxified prior to inclusion at much higher levels in the diet.

Excessive nitrogen volatilization from poultry litter as ammonia (NH₃) is harmful for chickens and poultry workers' health. Litter amendments such as bentonite and zeolite can reduce NH₃ and improve air quality in the poultry shed. Inclusion of these materials in poultry litter can reduce nitrogen volatilization and the solubility of phosphorus thus increasing the fertilizer value of the spent litter. To determine the extent to which the latter could be optimised we investigated the effect of high level inclusion of bentonite and zeolite in fresh pine shavings on broiler chicken live weight and welfare and a range of litter measurements including NH₃ production using the chamber acid trap method. The experiment ran for 42 days and had 5 treatments each replicated in two 2.25 m² pens with 25 chickens per pen. Treatments were nil amendment and 33% and 50% by weight addition of each of bentonite and zeolite. Inclusion of bentonite but not zeolite at these levels increased mortality of chickens during brooding, but did not adversely affect chicken live weight, footpad dermatitis, hock burn, breast blister and breast feathering of chickens up to day 42. Both amendments significantly reduced NH₃ in litter up to day 28. The effects of these amendments on the fertilizer value of the end of batch litter are under investigation.

Broiler chickens in Australia are traditionally reared on new litter. To increase resource utilization and improve production efficiency, industry is moving towards reusing litter in the shed for multiple batches. A study was conducted to compare the ammonia and dust production by meat chickens reared in new and reuse litter. Although Australian meat chicken industry increasingly establishing modern tunnel ventilated sheds, a vast majority of growers still using conventional sheds. Therefore, the study also investigated the dust and ammonia level in conventional and tunnel ventilated shed. To investigate the effect of shed type, ammonia concentration in ppm and particulate matter (dust) in mg/m³ of air was measured at various heights from the floor level and ages of chickens up week 7. Ammonia and dust levels were compared in new and reused litter in a separate experiment. The ammonia concentration was rapidly increasing with the age of chickens up to 3 weeks and then relatively steady up to week 5 without significant effect of shed type. The dust level was higher in conventional than tunnel shed. Overall, the dust level was increasing with the age of chickens up to week 5 and then steady or lower. The ammonia concentration in the reused litter was higher all along, whereas, dust level was higher in reused litter from week 3 and 4 but lower in week 2 and 5. Ammonia concentration always remained below the industry set limit of 25ppm.

A feeding study was conducted to compare the effects of litter material, dietary fibre and sex on growth performance, organ development, mucosal morphometry and gut microbial communities in broilers. Seven hundred twenty day old Cobb chicks were allocated to 24 floor pens in a 2 x 2 x 2 factorial design with 3 pens of 30 birds per replicate (3 pens of males and 3 pens of females). Factors were: litter material, paper or hardwood shavings; dietary fibre, low or high and sex. Diets consisted of wheat, soybean meal, meat meal, expeller canola meal, poultry fat, vitamin and minerals. Birds and feed were weighed on days 7, 21, and 35. Low fibre groups contained no oat hulls whereas high fibre groups contained 70 g/kg oat hulls. Birds grown on hardwood shavings had larger gizzards (P < 0.01) and a more favorable FCR (P < 0.03) than those grown on paper litter at 35 d. Dietary oat fibre was more beneficial in birds reared on paper litter than hardwood shavings as evidenced by significant fibre by litter interactions at 35 d for FCR (P < 0.02) and caecal 'C. perfringens' counts (P < 0.01). Dietary oat fibre improved body weight at 7 d (P < 0.04), and lowered gizzard pH (P < 0.02) at 35 d. The results suggest that the combination of clean paper litter with high oat fibre diet may be beneficial in enhancing gut health in broilers.

Many different litter materials are used as bedding for broiler chickens in Australia. In this study, the effect of litter type on the productivity and health of broilers was investigated. Broilers were reared on rice hulls, softwood sawdust, pine shavings, reused single-batch litter (originally based on pine shavings), hardwood sawdust, shredded paper or chopped straw. Litter type affected (P < 0.05) feed intake to 21 days of age. However, the performance of broilers on all the litter types was comparable at 42 days of age. This is consistent with the findings of Brake et al. (1993) and subsequent researchers who did not observe significant production differences associated with litter material.

A farmlet experiment was conducted between July 2000 and December 2006 as part of the Cicerone Project, which sought to enhance the profitability and sustainability of grazing enterprises on the Northern Tablelands of New South Wales, Australia. A self-replacing Merino enterprise was grazed as the dominant livestock enterprise, together with ~20% of the carrying capacity as cattle, on each of three farmlet treatments: higher levels of soil fertility and pasture renovation with flexible rotational grazing over eight paddocks (farmlet A), moderate soil fertility and pasture renovation with flexible rotational grazing over eight paddocks (farmlet B) and moderate soil fertility and pasture renovation with intensive rotational grazing over 37 paddocks (farmlet C). Prior to commencement of the trial, the three 53-ha farmlets were allocated equivalent areas of land based on soil type, slope and recent fertiliser history. This paper describes the effects of the three pasture and grazing management strategies on the production, quality and value of the wool produced per head, per ha and per farmlet. Up until 2001 there were no differences in wool production between farmlets. Thereafter, significant differences between farmlets emerged in greasy fleece weight per head and price received per kg of fleece wool. For example, the clean fleece value averaged over the 2003-05 shearings for all hoggets, ewes and wethers was 1531, 1584 and 1713 cents/kg for farmlets A, B and C, respectively. There were small but significant differences, which varied between sheep class and year, between the farmlets in average fibre diameter and staple length but less so with staple strength. In general, while the differences between farmlets in staple strength varied over time, farmlets A and B tended to have wool with longer staple length and broader fibre diameter than farmlet C and this affected wool value per kg. Differences in wool income per ha between farmlets grew in later years as the farmlet treatments took effect. In spite of farmlet A having a slightly lower wool value per kg, after taking into account its greater fleece weight per head and its higher stocking rate, the total wool income per ha was higher than on either farmlets B or C. The average gross wool income per ha from 2003 to 2005 was $303, $215 and $180 for farmlets A, B and C, respectively. The highest amount of greasy wool produced was in 2004 when 38.2, 26.5 and 21.5 kg/ha was harvested from farmlets A, B and C, respectively. The fibre diameter profiles of 2-year-old ewes showed similar profiles for farmlets A and B but a significantly finer fibre diameter profile for farmlet C ewes due to intensive rotational grazing. However, sheep on all three farmlets produced wool with high staple strength. Multivariate analyses revealed that greasy fleece weight, staple length and staple strength were significantly positively correlated with the proportion of the farm grazed at any one time, and with soil phosphorus, legume herbage and green digestible herbage thus highlighting the significant influence of pasture and soil inputs and of grazing management on wool production and quality.

As part of the Cicerone Project's whole-farmlet experiment on the Northern Tablelands of New South Wales, Australia, the fat scores and reproductive performance of ewes were measured to assess the effect of different management systems on these important production parameters over time. The three farmlets (each of 53 ha) included one (farmlet B) subjected to 'typical' district management consisting of moderate levels of inputs and a target stocking rate of 7.5 dse/ha, with flexible grazing management across eight paddocks. A second farmlet (A) was managed in a similar fashion to farmlet B with respect to number of paddocks and grazing management, but modified by high rates of pasture renovation and higher levels of soil fertility, with a target stocking rate of 15 dse/ha. The third farmlet (C) was managed at the same level of moderate inputs as farmlet B but employed intensive rotational grazing over 37 paddocks and also had a high target stocking rate of 15 dse/ha. The experiment was conducted over 6.5 years from July 2000 to December 2006. In spite of the fact that target levels of stocking rate were chosen at the beginning of the experiment, stocking rate, together with fat scores and reproduction were treated as emergent properties of each farmlet system. Joining took place in April-May and lambing occurred in September-October of each year. Over the first 2 years of the experiment, there were few differences among farmlets in ewe fat scores or reproductive performance. From 2003 onwards, while the percentage of ewes pregnant was similar between farmlets, the average proportion of multiple births (ewes scanned in late July, with twins) was 30%, 16% and 12%, respectively, on farmlets A-C. However, lamb losses were greater on farmlet A, with average lamb mortalities recorded on farmlets A-C of 29%, 10% and 19%, respectively. Over the duration of the experiment, ewes on farmlets A and B were more often above a fat score level of 3, and less often below 2.5, than were ewes from farmlet C. Differences among farmlet ewes in fat score were found to be significant in 7 of the total of 13 assessments over the duration of the experiment. A generalised additive model applied to whole-farmlet data showed that green digestible herbage, legume herbage, stocking rate, the amount of supplement fed and especially the proportion of each farmlet grazed at any one time all influenced fat scores of ewes. While fat scores and conception rates tended to be highest on farmlet A, farmlet B had slightly better reproductive outcomes due to less lambing losses, whereas ewes on farmlet C tended to have somewhat lower fat scores and levels of reproduction. These farmlet-scale findings highlighted the importance for livestock managers to focus not only on grazing management, stocking rate and stock density during lambing, but also on the availability of sufficient green, and especially legume herbage, and the difficulty of overcoming a deficit in quality herbage with supplementation.

The effect of two vaccine strains of infectious bronchitis virus (IBV - VicS and A3 strains) on internal and external quality of eggs was studied in Isa Brown hens in full lay. Birds were either unvaccinated for IBV or had been vaccinated during rearing. The main effects of exposure to the vaccine viruses were that VicS resulted in paler coloured shells, mainly in the unvaccinated birds and the eggs from the hens challenged with VicS were more elongate than the other groups. These findings are consistent with our earlier findings with field strains of IBV and differ from those reported in the literature for different strains of IBV.

We investigated the effects of adding alum, sodium bisulphate, bentonite, zeolite and NaturClean CSM® at 3.2, 3.2, 13, 13 and 0.9 % by weight respectively to reused litter on moisture content, pH, ammonia production, bird liveweight and conditions linked to welfare including scores for footpad dermatitis, hock burn, breast burn and breast feathering. Treatments, including no amendment, were applied to four pens each 2.25 m² with half the pens having 20% additional water added. Nineteen broiler chicks were reared in each pen up to day 42 with sampling of the litter and birds at various intervals. Litter moisture content of 31% on day 0, reduced to approximately 21% on days 7 and 14 before increasing to a value of 53% on day 42. All litter amendments except NaturClean CSM® reduced ammonia production with the greatest reductions seen with alum and sodium bisulphite on days 7 and 14. Amendments worked similarly in litter with or without water addition. There were no significant effects of litter amendment on bird weights or measures of welfare with welfare measures generally worsening with time and with initial addition of water. Ranking of reused litter treatments from 1 to 6 (best to worst) for each welfare measure, followed by the averaging of those rankings, provided mean rankings of 1.75, 2.25, 3, 3.75, 4.75 and 5.5 respectively for reused litter without amendment, bentonite, alum, sodium bisulphite, NaturClean CSM® and zeolite treatments. Both acidifying and adsorbent litter additives have potential to significantly reduce ammonia concentrations on reused litter. Further work is required to determine optimum inclusion rates and more clearly identify effects on welfare and performance.

Genetic parameters for liveweight (LWT), greasy fleece weight (GFW), mean fibre diameter (MFD), standard deviation of MFD (MFD-s.d.), mean fibre curvature (CURVE) percentage of medullated (%MED) and kemp (%KEMP) fibres, faecal worm egg count (WEC), packed cell volume (PCV), mean corpuscular volume (MCV) mean corpuscular haemoglobin content (MCHC), circulating anti-nematode IgG (IgG) and counts of circulating eosinophils (EOS), lymphocytes (LYM), neutrophils (NEU), basophils (BASO) and monocytes (MONO) up to 18 months of age were estimated in Australian Angora goats (608 animals, 14 sires 3 years of birth). Measurements were made during a period of natural parasite challenge up to 5 months of age, or following artificial challenge with 10 000 infective larvae of 'Trichostrongylus colubriformis' at 5.25 months of age. Year of birth had a significant impact on production and parasite-associated traits at all ages studied. Sex had a marked effect on production and erythrocyte traits. Birth type had no effect on any traits in animals older than 6 months. Maternal effects were not significant except for LWT at 3, 5 and 6 months and for IgG at 3 months. Most production traits were highly (LWT, GFW, MFD,%MED)or moderately (CURVE, MFD-s.d.) heritable (range 0.17–0.59) with only %KEMP having a low heritability (0.02–0.14). The heritability estimates (±s.e.) for CURVE are novel for goats and ranged from 0.18 ± 0.09 at first shearing to 0.44 ± 0.14 at third shearing. Heritability estimates were low forWEC(0.02–0.16) and for specific IgG during natural infection (0.14-0.15) but higher for IgG following artificial challenge with 'T. colubriformis' (0.42 ± 0.13). Of the haematological variables NEU and all red cell traits were highly heritable (0.45–0.71), LYM and MONO were moderately to highly heritable (0.31–0.55), and EOS was weakly to moderately heritable (0.06–0.28). Strong phenotypic correlations existed between production traits. MFD was positively correlated with GFW and negatively correlated with CURVE, indicating that finer fibres have a higher crimp or wave count. WEC had consistent negative phenotypic correlations with PCV, LYM and EOS, and positive correlations with NEU. Correlations with IgG were positive up to 5 months and negative thereafter. Phenotypic correlations between WEC and LWT as well as with GFW and MFD were negative. Heritability estimates for production traits were generally consistent with other studies. Haematological and fibre curvature findings are completely novel for Angora goats. Estimates of heritability for WEC fell in mid range of published findings for other goat breeds, and these results suggest that there is some scope for breeding for worm resistance in Angoras but the response is likely to be slow.

The present study was designed to estimate genetic parameters of 17 production, parasite-associated and haematological traits in Australian cashmere goats. It comprised 796 records of female progeny of 532 dams sired by 29 bucks over a 4-year period. Measurement of haematological and parasite-associated traits was carried out on female kids during low-level natural gastrointestinal nematode challenge at 3 and 5 months of age and at 28 and/or 35 days after artificial challenge with 10 000 infective larvae of 'Trichostrongylus colubriformis' administered 1 week after the 5-month measurement. Production traits were measured up to 18 months of age. Year of birth significantly affected all traits apart from cashmere diameter (CSD). Twin kids had significantly lower liveweight (up to 10 months), packed cell volume and mean corpuscular volume (at 3 and 5 months) but higher specific IgG levels and mean corpuscular haemoglobin content at 3 months. Paddock of birth and early rearing and its interaction with year of birth had significant effects on worm egg count (WEC) during natural challenge, on IgG at both natural and post-artificial challenge measurements and on liveweight at early ages. The level of gastrointestinal nematode challenge in the nine different paddocks clearly influenced both WEC and IgG during natural and subsequent artificial challenge. Maternal permanent environmental effects were important only for liveweights at 3 month of age and for IgG at 5 months of age. For other traits, a simple animal model without maternal permanent environmental effects gave the best fit. Estimates of heritability (h²) of WEC and IgG were low (0.06–0.22) with the highest h² estimates occurring after 5 months of natural infection or 35 days after artificial challenge. The majority of fleece traits were moderately to highly heritable, ranging from 0.38 to 0.78. The h² estimates for mean fibre curvature are novel for cashmere goats and were moderate, varying from 0.32 to 0.48. Heritability estimates for erythrocyte traits were uniformly high (0.49–0.98) while those for leukocyte traits varied from low to moderate (0.09–0.43). Strong genetic and phenotypic correlations existed between major production traits. Due to the comparatively small dataset, the standard errors of genetic correlations were relatively high. CSD was positively correlated with cashmere weight and yield, an unfavourable direction. CSD was negatively correlated with fibre curvature, indicating that animals producing finer fibres produce cashmere with a higher crimp count. No phenotypic relationships were observed between WEC and fleece traits. Liveweight was weakly but negatively correlated with WEC and circulating neutrophils, while it was positively associated with eosinophils, lymphocytes and packed cell volume. This study has shown that selection for increased resistance to gastrointestinal nematode infection cashmere goats is possible but progress will be slow. WEC should remain the phenotypic marker of choice and the additional cost of alternative measures of resistance is not justified. Many of the parasite-associated traits appear to under independent genetic control.

The incubation period (21 d) represents about 37 % of the entire lifespan of the modern broiler bird. Organ and overall body development during incubation are related to the final market weight. The technology for in ovo feeding has been largely developed (Uni and Ferket, 2003) but the uptake rate is slow. This may partly be due to lack of suitable nutrients, which not only promote pre- and post-hatch growth but can support good hatchability. In the present study, 0.5 ml of a solution of betaine was injected into standard size 18 d embryonated broiler eggs at 10, 50, 100 and 200 mg betaine per egg. There were un-injected control eggs and sham control eggs injected with 0.5 ml Milli-Q water. The eggs were re-set to hatch and chicks were maintained in their respective groups and fed on a standard diet (based on sorghum and maize) to 21 d of age.

A dog's nutrient requirements can theoretically be met from a properly balanced meat-free diet; however, proof for this is lacking. Exercise places additional demands on the body, and dogs fed a meat-free diet may be at increased risk of developing sports anaemia. We hypothesised that exercising dogs would remain in good health and not develop anaemia when fed a nutritionally balanced meat-free diet. To this end, twelve sprint-racing Siberian huskies were fed either a commercial diet recommended for active dogs ('n' 6), or a meat-free diet formulated to the same nutrient specifications ('n' 6). The commercial diet contained 43% poultry meal, whereas soyabean meal and maize gluten made up 43% of the meat-free diet, as the main protein ingredients. Dogs were fed these diets as their sole nutrient intake for 16 weeks, including 10 weeks of competitive racing. Blood samples were collected at weeks 0, 3, 8 and 16, and veterinary health checks were conducted at weeks 0, 8 and 16. Haematology results for all dogs, irrespective of diet, were within normal range throughout the study and the consulting veterinarian assessed all dogs to be in excellent physical condition. No dogs in the present study developed anaemia. On the contrary, erythrocyte counts and Hb values increased significantly over time (P<0·01) in both groups of dogs. The present study is the first to demonstrate that a carefully balanced meat-free diet can maintain normal haematological values in exercising dogs.

The increasing use of computer technology in industry and society has been mirrored in Australian higher education most obviously in organisational management, but it also plays a significant role in the delivery of courses and management of student participation. The growing trend to Distance Education has played a pivotal role in this. Perhaps less obvious has been the growing use, in teaching and research, of computer simulation modelling applications and similar electronic decision support tools (DSTs), many of which are used in industry. For teaching purposes many of these DSTs are intended to simulate 'real world' issues and situations for students. The eDST project developed from the recognition, among university teachers of agricultural science and related degrees across Australia, that simulation software programs were being incorporated into subjects/units as valuable learning experiences for undergraduate students. Over the last ten years various arrangements or mechanisms have been used for the delivery of such programs, in most cases supported by special funding. In general, once the funding support was finished, these initiatives were unsustainable. The eDST project sought to explore the technical, business and pedagogical issues around sharing applications (particularly commercial ones) across the university sector in Australia.

This paper gives an overview of the education environment in Australia and in particular, sheep and wool science education. It includes the results of a survey of the industry’s future needs for graduates and outlines the developments in e-learning. The Sheep Industry CRC education program is aimed at building future human capability in the sheep industry by training postgraduates, delivery of a national program of sheep and wool degree units available for students at most universities to study by distance education, and developing VET and school resources. A new Bachelor of Livestock Science degree was developed at the University of New England to enable students to specialise in animal breeding, health and nutrition and sheep and wool science. TAFE and school outcomes include the development of learning materials, training programs, teacher professional development as well as resources to promote careers in the sheep industry. The integration of the use of material across sectors is also discussed.

A six-year study on 50 ha farmlets on the northern tablelands of NSW compared control of gastrointestinal nematode (GIN) infection of sheep under typical (TYP), high input (HI) or intensive rotational grazing (IRG) management systems. The major sources of variation in faecal worm egg count (WEC) were also examined. The data set comprised 5644 faecal worm egg count (WEC) records and 322 larval differentiation tests. Worm infections in ewes, lambs, hoggets and wethers were, with some exceptions, adequately controlled through a combination of regular monitoring of WEC, anthelmintics and grazing management. The IRG farmlet had lower mean WEC (444 epg) and annual anthelmintic treatment frequency (3.1 treatments/yr) over the whole experimental period than TYP (1122 epg, 4.3 treatments/yr) or HI (1374 epg, 4.7 treatments/yr). The main factors influencing WEC were the time since the last anthelmintic treatment, and the anthelmintic used at that treatment. The magnitude of these effects dwarfed those climatic and management factors that might be expected to influence the epidemiology of GIN infections via environmental or host-mediated mechanisms. Nevertheless management factors associated with stocking rate and grazed proportion (proportion of each farmlet grazed at any one time), and climatic indicators of both temperature and moisture availability had significant effects on WEC. The results show that in a region with 'Haemonchus contortus' as the major GIN, improved host nutrition under the HI system did not provide more effective control of GIN than typical management, while IRG did provide considerably better control. Tactical worm control based on WEC monitoring provided adequate control of worms on all three farmlets for much of the experimental period but failed to prevent significant spikes in WEC on the TYP and HI farmlets to values associated with significant production loss on multiple occasions, and mortality on one occasion.

Characterization of genetic diversity and evolutionary history provides a low level handle on population structure which can be used to make decisions on how these populations will be managed. This has immediate implications for natural populations in conservation programs but is also highly relevant for Agricultural species. We used 29,844 SNPs to estimate genetic variability in 3 subpopulations of Hanwoo cattle (Jeju Black, Brindle and Brown) and their genetic distances to seven other breeds (Chinese Yeonbyun, Brahman and 5 European breeds). Jeju Black and Brindle, small isolated populations, are evidencing clear signs of island population effects with high FST=0.06 between them (FST between European and Eastern Asian breeds is Δ0.085) and Δ0.03 with the continental Brown. This may lead to negative consequences and even endanger these subpopulations in the future. Eastern Asian breeds show a relatively small genetic background originating from 'Bos indicus' which is identifiable in both Hanwoo and Yeonbyun (~5-10%). This suggests that at some point during radiation of 'Bos taurus' throughout Eastern Asia they crossed with zebu cattle radiating from India which contributed to the final genetic architecture of these breeds. Brown Hanwoo and Yeonbyun are genetically highly related with the latter showing higher levels of diversity which may be due to lack of intense artificial selection. This makes Yeonbyun cattle worthy of attention since they could potentially act as proxies to the ancestral Hanwoo prior to selection and assist in characterization of ancestral alleles in Hanwoo. This close relationship can reduce noise and lead to more robust identification of recent signatures of selection due to breeding for production traits, particularly marbling. Good genetic characterization of the Chinese breed can also be beneficial for genomic selection in Hanwoo which will benefit by being able to better distinguish genotypes between identity by descent and identity by state.

Systems that produce beef are quite heterogeneous, involving different breed types, widely differing environments, a range of market demands and considerable production derived from dairy industries. This contrasts with the pig and poultry industries where there are generally few decision makers, well-directed pursuit of goals and much less variation in production systems, the environment and, in most cases, the market. In major temperate beef-producing countries such as the USA, Canada, parts of South America, New Zealand and parts of Australia, beef production is based on extensively grazed or ranched cows, mainly of pure British beef breeds like the Hereford, Angus and Shorthorn, or crosses of these breeds. In some of these countries, like the USA, Canada and parts of Australia, this extensive pre-weaning regime is usually followed by a more intensive finishing period in feedlots. The extensive nature of many production systems, and the widespread use of crossbred animals in the commercial sector of most beef industries means that performance recording and genetic improvement are usually concentrated in a relatively small sector of the population.

The suggestion by Land (1973) that it might be possible for genes with positive effects on female reproductive performance to be identified in males, has provided the stimulus for many studies in sheep populations throughout the world. The review of literature (Chapter 1) established, however, that these studies have largely been restricted to between-breed comparisons or within sheep populations which have been selected for components of reproduction rate. The review of literature also established that, although physiological and endocrine aspects of gonadal growth and function in rams has been extensively studied, relatively little research has been directed at sources of variation in male reproductive traits with a view to estimating genetic parameters. A similar situation was found when the literature relating to ram libido and serving capacity was reviewed. The aim of the studies described in Chapters 3 and 4 of this thesis was to identify, in a large random breeding Merino flock maintained at Trangie, NSW, the sources of variation in measures of gonadal growth and serving capacity, and to estimate genetic parameters for these traits. Utilising appropriate variances from these studies and other sources, an investigation (Chapter 5) was conducted, aimed at quantifying the genetic relationship between male and female measures of reproductive performance. The study described in Chapter 6 is the result of an investigation of a related aspect of male and female genetic relationships.

It is sometimes possible to breed for more uniform individuals by selecting animals with a greater tendency to be less variable, that is, those with a smaller environmental variance. This approach has been applied to reproduction traits in various animal species. We have evaluated fecundity in the Irish Belclare sheep breed by analyses of flocks with differing average litter size (number of lambs per ewe per year, NLB) and have estimated the genetic variance in environmental variance of lambing traits usingdouble hierarchical generalized linear models (DHGLM). The data set comprised of 9470 litter size records from 4407 ewes collected in 56 flocks. The percentage of pedigreed lambing ewes with singles, twins and triplets was 30, 54 and 14%, respectively, in 2013 and has been relatively constant for the last 15 years. The variance of NLB increases with the mean in this data; the correlation of mean and standard deviation across sires is 0.50. The breeding goal is to increase the mean NLB without unduly increasing the incidence of triplets and higher litter sizes. The heritability estimates for lambing traits were NLB, 0.09; triplet occurrence (TRI) 0.07; and twin occurrence (TWN), 0.02. The highest and lowest twinning flocks differed by 23% (75% versus 52%) in the proportion of ewes lambing twins. Fitting bivariate sire models to NLB and the residual from the NLB model using a double hierarchical generalized linear model (DHGLM) model found a strong genetic correlation (0.88 ± 0.07) between the sire effect for the magnitude of the residual (VE) and sire effects for NLB, confirming the general observation that increased average litter size is associated with increased variability in litter size. We propose a threshold model that may help breeders with low litter size increase the percentage of twin bearers without unduly increasing the percentage of ewes bearing triplets in Belclare sheep.

No matter how far science advances, the proportion of what is knowable to what is random will remain unchanged, and attempts to ignore this critical threshold are futile at best. With the revolutionary explosion in genetic information discovery, it is crucially important to recognize the underlying limitations of scientific prediction in genetics. Genetics and Randomness furthers the understanding of the role randomness plays in critical biological processes. The book also navigates the complex nature of genetic uncertainty from different points of view and at various levels of biological organization. Exploring areas ranging from basic quantum mechanics and molecular genetics to modern evolutionary genetics and the philosophy of mathematics, this well-organized text discusses: ●Spontaneity of mutations and their relation to subatomic randomness ●Deep links between subatomic fluctuations and long-term macroscopic changes in living organisms ●The multitude of random events that occur during development ●Segregation, genetic drift, and natural selection Randomness and uncertainty are not occasional and regretful deviations from the "true" principles upon which life is built. Genetics and Randomness illustrates the ubiquitous nature of randomness as an integral feature of all essential processes, effectively embracing a probabilistic understanding of the phenomena of life.

The purpose of this book is to present in one location a complete, comprehensive and updated description of the modern genetics of the pig. It is our intention to combine essential knowledge from the various fields of genetics and biology of the pig, integrated with livestock management aspects, in order to provide an updated and informative reference book. The genetic improvements in the pig industry over the past couple of decades have been very impressive, with growth rates increasing, feed efficiency improving and a continued rise in overall leanness. These successes have in great part been due to the incredible progress in the understanding and application of genetics to pig production. As recently as 1990, only about 50 genes and markers were mapped or assigned to individual porcine chromosomes. Now the genome draft sequence has been obtained and the completion of very detailed genetic and genomic maps has been accomplished. Furthermore, genetic improvement within the pig industry that rests on the introduction of gene tests and on genomic selection based on thousands of genes is coming. This book is addressed to a diverse audience, including students, researchers, veterinarians and pig breeders.

Genome-wide association studies (GWAS) have rapidly spread across the globe over the last few years becoming the de facto approach to identify candidate regions associated with complex diseases in human medicine. GWAS and genome analysis are also powerful tools to provide a handle on genetic variation in a wide range of traits important for human health, agriculture, conservation, and the evolutionary history of life. As the technology matured and results from the various studies came to light, a clear picture emerged that, as often seems to be the case, biological processes prove to be much more complex than we would want them to be. While many new insights were and are being attained, maybe just as many new questions emerged. In many cases, GWAS successfully identified variants that were unquestionably associated with variation in traits and, in some cases, culminated in the discovery of the causal variant(s) and its mechanism of action. In other cases, these studies evidenced that a large number of traits are highly polygenic, and, instead of identifying a few genomic region 'culprits', we saw a scattering of effects across the whole genome. While in these latter cases the underlying biology largely remains elusive, it still allows making predictions of phenotypes based on the genomic information of an individual. And this in the short term might be even more important for translational outcomes. This brings us to the focus of this volume in the series 'Methods in Molecular Biology: Genome-Wide Association Studies and Genomic Prediction'. This volume in the series covers from the preliminary stages of understanding the phenotypes of interest and design issues for GWAS, passing through efficient computational methods to store and handle large datasets, quality control measures, phasing, haplotype inference and imputation, and moving on to then discuss the various statistical approaches to data analysis where the experimental objective is either to nail down the biology by identifying genomic regions associated to a trait or to use the data to make genomic predictions about a future phenotypic outcome (e.g. predict onset of disease).

Background: Body weight (BW) is an important trait for meat production in sheep. Although over the past few years, numerous quantitative trait loci (QTL) have been detected for production traits in cattle, few QTL studies have been reported for sheep, with even fewer on meat production traits. Our objective was to perform a genome-wide association study (GWAS) with the medium-density Illumina Ovine SNP50 BeadChip to identify genomic regions and corresponding haplotypes associated with BW in Australian Merino sheep. Methods: A total of 1781 Australian Merino sheep were genotyped using the medium-density Illumina Ovine SNP50 BeadChip. Among the 53 862 single nucleotide polymorphisms (SNPs) on this array, 48 640 were used to perform a GWAS using a linear mixed model approach. Genotypes were phased with 'hsphase'; to estimate SNP haplotype effects, linkage disequilibrium blocks were identified in the detected QTL region. Results: Thirty-nine SNPs were associated with BW at a Bonferroni-corrected genome-wide significance threshold of 1 %. One region on sheep ('Ovis aries') chromosome 6 (OAR6) between 36.15 and 38.56 Mb, included 13 significant SNPs that were associated with BW; the most significant SNP was OAR6_41936490.1 (P = 2.37x10−16) at 37.69 Mb with an allele substitution effect of 2.12 kg, which corresponds to 0.248 phenotypic standard deviations for BW. The region that surrounds this association signal on OAR6 contains three genes: 'leucine aminopeptidase 3' (LAP3), which is involved in the processing of the oxytocin precursor; 'NCAPG non-SMC condensin I complex, subunit G (NCAPG)', which is associated with foetal growth and carcass size in cattle; and 'ligand dependent nuclear receptor corepressor-like (LCORL)', which is associated with height in humans and cattle. Conclusions: The GWAS analysis detected 39 SNPs associated with BW in sheep and a major QTL region was identified on OAR6. In several other mammalian species, regions that are syntenic with this region have been found to be associated with body size traits, which may reflect that the underlying biological mechanisms share a common ancestry. These findings should facilitate the discovery of causative variants for BW and contribute to marker-assisted selection.

Body weight (BW) is an important trait for meat production in sheep. In order to clarify genes and chromosomal regions that might be associated with body weight in sheep, a genome-wide association study using Illumina 50K Ovine SNP chip on a population of 1,743 Australian Merino sheep was carried out. A total of 39 SNPs were found to be associated with BW at Bonferroni-corrected genome-wide significance of 1%. One region on OAR6, between 40.3 Mb and 42.9 Mb, included 13 significant SNPs that were identified as being associated with the trait. The most significant SNP (OAR6_41936490.1) has 2.11 kg of allele substitution effect, while the second most significant SNP (s17946.1) has 2.13 kg of effect on body weight. These correspond to 24.33% and 24.57%, respectively, of the phenotypic standard deviations for BW in Australian Merino sheep.

In this paper we proposed a method to improve the accuracy of prediction of genomic best linear unbiased prediction (GBLUP). In GBLUP a genomic relationship matrix (GRM) is used to define the variance-covariance relationship between individuals and is calculated from all available genotyped markers. Instead of using all markers to build the GRM, which is then used for trait prediction, we used an evolutionary algorithm (differential evolution - DE) to subset the marker set and identify the markers that best capture the variance-covariance structure between individuals for specific traits. This subset of markers was then used to build a trait relationship matrix (TRM) that replaces the GRM in GBLUP (herein referred to as TBLUP). The predictive ability of TBLUP was compared against GBLUP and a Bayesian method (Bayesian LASSO) using simulated and real data. We found that TBLUP has better predictive ability than GBLUP and Bayesian LASSO in almost all scenarios.

Managing infections of sheep with gastrointestinal nematode parasites (worms) and problems of resistance to anthelmintic treatments continue to be major challenges for graziers on the Northern Tablelands of New South Wales, Australia. The whole-farmlet study of grazing enterprises undertaken by the Cicerone Project tested the broad hypotheses that compared with typical management (farmlet B), internal parasites can be more effectively managed with improved nutrition (farmlet A) or by intensive rotational grazing (farmlet C). Further aims were to identify the major sources of variation in faecal worm egg count (WEC) over the 6-year period and to examine the efficacy of the various anthelmintic treatments used during the experiment. This paper describes the management of sheep worms at the whole-farmlet level during the experiment, and analyses data from the routine WEC monitoring (5644 records) and larval differentiation tests (322 records) carried out on behalf of the Cicerone Management Board and by a doctoral candidate. It complements more detailed investigations published elsewhere. Over the period from July 2000 to December 2006, worm infections in ewes, lambs, hoggets and wethers were, with some exceptions, successfully controlled on the farmlets through a combination of regular monitoring of WEC, treatment with a wide array of anthelmintics and grazing management. Farmlet C had lower mean WEC (444 epg) and annual anthelmintic treatment frequency (3.1 treatments/year) over the whole experimental period than farmletsB(1122 epg, 4.3 treatments/year) or A (1374 epg, 4.7 treatments/year). The main factors influencing WEC were the time since the last anthelmintic treatment, and the anthelmintic used at that treatment. The magnitude of these effects dwarfed those of climatic and management factors that might be expected to influence the epidemiology of gastrointestinal nematode infections via environmental or host-mediated mechanisms. Nevertheless management factors associated with stocking rate and grazed proportion (proportion of each farmlet grazed at any one time), and climatic indicators of both temperature and moisture availability had significant effects on WEC. The results show that, in a region with 'Haemonchus contortus' as the major sheep nematode, improved host nutrition in a higher input system (farmlet A) did not provide more effective control of gastrointestinal nematodes than typical management (farmlet B); however, it was observed that gastrointestinal nematode control was no worse on farmlet A than on farmlet B in spite of farmlet A supporting a 48% higher stocking rate by later in the trial period (2005). The study provided strong support for the proposition that intensive rotational grazing (farmlet C) provides more effective control of gastrointestinal nematodes than typical management (farmlet B) as evidenced by significantly lower WEC counts and anthelmintic treatment frequency. Tactical worm control based on routine monitoring of WEC provided adequate control of worms on all three farmlets for much of the experimental period but failed to prevent significant spikes in WEC to values associated with significant production loss on multiple occasions, and significant ewe mortality on farmlets A and B on one occasion.

A study was conducted to determine the predictability of energy balance and energy efficiency by using dietary chemical composition. Closed-circuit indirect calorimetry was used to determine the apparent metabolisable energy (AME), respiratory quotient, heat increment (HI), net energy (NE) and ratio of NE to AME (NE : AME) of a series of diets with varying levels of chemical constituents. Diets were analysed for DM, gross energy, protein, fat, ash, crude fibre, acid detergent fibre, neutral detergent fibre, starch, sugars (mono- and disaccharides), and soluble, insoluble and total non-starch polysaccharides. Ross 308 male broilers were acclimatised to chambers and diets for 3 days and 12 days, respectively, before O₂ consumption and CO₂ expiration were measured gravimetrically. Gross energy of feed consumed and excreta voided were measured and AME was calculated. Heat production was calculated using the Brouwer equation based on O₂ and CO₂. After taking fasting heat production into account by using a value of 450 kJ/BW⁰˙⁷⁰, HI was determined. NE was calculated as AME minus HI. The results showed high predictability of AME (R² = 0.89) and NE (R² = 0.85) by using chemical components. HI was less predictable (R² = 0.25). Efficiency of energy utilisation (NE : AME) was predicted (R² = 0.40). Closed-circuit calorimetry was found to be useful for evaluating the contribution of the chemical components of feed ingredients to the efficiency of energy utilisation in broilers. These results may be used to reduce energy costs in broiler feed formulation.