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Journal ArticlePublication Divergent breeding values for fatness or residual feed intake in Angus cattle. 1. Pregnancy rates of heifers differed between fat lines and were affected by weight and fat(CSIRO Publishing, 2018) ;Jones, F M ;Accioly, J M ;Copping, K J ;Deland, M P B ;Graham, J F ;Hebart, M L; ;Laurence, M ;Lee, S J ;Speijers, E JPitchford, W SThe pregnancy rate of heifers affects the efficiency and profitability of beef herds. Heifers extreme in rib fatness (Fat) or post-weaning residual feed intake (RFI) estimated breeding values (EBVs) were evaluated for their pregnancy rates at two locations in the southern agricultural regions of Australia (Struan and Vasse) as part of the Beef Cooperative Research Centre Maternal Productivity Project. Heifers divergent in Fat (High-Fat and Low-Fat) had differences in fat depth pre-joining at the 12/13th rib (4.4 mm vs 3.5 mm) and P8 rump site (6.1 mm vs 4.8 mm). This was associated with significant differences in pregnancy rates over a 9-week joining period (91.5% vs 83.0%) and an even larger difference when calculated over a 6-week joining period (77.3% vs 65.0%). Heifers divergent in RFI (Vasse only) also differed in rib fat (7.6 mm vs 6.4 mm) and P8 fat (11.0 vs 9.2 mm), but not significantly in pregnancy rates between the two RFI (High-RFI and Low-RFI) genotypes following a 9-week (92.4% vs 88.5%) or 6-week (81.2% vs 73.7%) joining period. The phenotypic analysis of the Fat and RFI heifers together indicated that weight and fat depth were the largest contributing factors to variation in pregnancy rates, and age and pre-joining weight gain were not significant. These phenotypic characteristics indicated that producers can manage heifers to particular weight and fat combinations to improve heifer conception rates. Associations of BREEDPLAN EBVs with heifer fertility showed that a shorter days-to-calving EBV had the biggest impact (P < 0.001) on heifer pregnancy rates and rib fat and scrotal size EBVs were close to significant (P < 0.10).
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Journal ArticlePublication Divergent genotypes for fatness or residual feed intake in Angus cattle. 2. Body composition but not reproduction was affected in first-parity cows on both low and high levels of nutrition(CSIRO Publishing, 2018) ;Laurence, M ;Accioly, J M ;Copping, K J ;Deland, M P B ;Graham, J F ;Hebart, M L; ;Jones, F M ;Lee, S J ;Speijers, E JPitchford, W SThis paper reports a subset of results from the Beef Cooperative Research Centre-funded Maternal Productivity Project. This research aimed to describe the response of Angus cows of different and divergent genotypes to variable nutritional environments over five breeding seasons. Cows selected for a divergence in either fat depth (HFat vs LFat) or residual feed intake (RFI: HRFI vs LRFI) based on mid-parent estimated breeding values (EBV) for those traits were allocated in replicate groups to either high or low nutritional treatments at two different sites, namely the Vasse Research Centre in western Australia and the Struan Research Centre in South Australia. The traits reported in this paper include output traits (birth and weaning weight of calves, live weight change of cows), change traits (change in Rib Fat, P8 fat, eye muscle area and live weight between specified time points) and reproductive traits [pregnancy rates, percentage calves born alive and days to calving at the days to calving at the second calving opportunity (DC2)]. Having had their first calf, the vulnerability of these young cows to nutritional restriction and how it may adversely affect rebreeding was examined. HFat and HRFI cows were fatter, heavier and had greater eye muscle area than LFat and LRFI, respectively, at all times during the breeding cycle on both levels of nutrition. There was no difference in either days-to-calving or pregnancy rates after the second mating between genotypes. Equally, nutritional treatment had no effect on these traits in this cohort of cows. There was evidence for an implied genetic correlation between Rib Fat EBV, DC2 and pregnancy rates of –0.38 that suggests that selection for leanness may result in reduced fertility of the herd but the effect was not significant herein. As long as producers record the phenotype for both traits and select cows with favourable DC2 as well as low fatness, these problems can be avoided, owing to only 22% of variation in pregnancy rates being explained by DC2 and Rib Fat EBV. Producers can largely be confident that selection for leanness, or increased feed efficiency, has little impact on productivity as long as cows are in adequate body condition to remain healthy and productive.
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Journal ArticlePublication Genetic variation in residual feed intake is associated with body composition, behavior, rumen, heat production, hematology, and immune competence traits in Angus cattle(American Society of Animal Science, 2019-05); ;Velazco, Jose I ;Smith, Helen ;Arthu, Paul F ;Hine, Brad; ; This experiment was to evaluate a suite of biological traits likely to be associated with genetic variation in residual feed intake (RFI) in Angus cattle. Twenty nine steers and 30 heifers bred to be divergent in postweaning RFI (RFIp) and that differed in midparent RFIp -EBV (RFIp-EBVmp) by more than 2 kg DMI/d were used in this study. A 1-unit (1 kg DM/d) decrease in RFIp -EBVmp was accompanied by a 0.08 kg (SE = 0.03; P < 0.05) increase in ADG, a 0.58 kg/d (0.17; P < 0.01) decrease in DMI, a 0.89 kg/kg (0.22; P < 0.001) decrease in FCR, and a 0.62 kg/d (0.12; P < 0.001) decrease in feedlot RFI (RFIf). Ultrasonically scanned depths of subcutaneous fat at the rib and rump sites, measured at the start and end of the RFI test, all had strong positive correlations with RFIp -EBVmp, DMI, and RFIf (all r values ≥0.5 and P < 0.001). Variation in RFIp -EBVmp was significantly correlated (P < 0.05) with flight speed (r = −0.32), number of visits to feed bins (r = 0.45), and visits to exhaled-emission monitors (r = −0.27), as well as the concentrations of propionate (r = −0.32) and valerate (r = −0.31) in rumen fluid, white blood cell (r = −0.51), lymphocyte (r = −0.43), and neutrophil (r = −0.31) counts in blood. RFIp -EBVmp was also correlated with the cellular immune response to vaccination (r = 0.25; P < 0.1) and heat production in fasted cattle (r = −0.46; P < 0.001). Traits that explained significant variation (P < 0.05) in DMI over the RFI test were midtest metabolic-BW (44.7%), rib fat depth at the end of test (an additional 18%), number of feeder visits (additional 5.7%), apparent digestibility of the ration by animals (additional 2.4%) and white blood-cell count (2.1%), and the cellular immune response to vaccine injection (additional 1.1%; P < 0.1), leaving ~23% of the variation in DMI unexplained. The same traits (BW excluded) explained 33%, 12%, 3.6%, 3.7%, and 3.1%, and together explained 57% of the variation in RFIf. This experiment showed that genetic variation in RFI was accompanied by variation in estimated body composition, behavior, rumen, fasted heat production, hematology, and immune competence traits, and that variation in feedlot DMI and RFIf was due to differences in BW, scanned fatness, and many other factors in these cattle fed ad libitum and able to display any innate differences in appetite, temperament, feeding behavior, and activity
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Publication Open AccessJournal ArticleNon-starch polysaccharide-degrading enzymes may improve performance when included in wheat- but not maize-based diets fed to broiler chickens under subclinical necrotic enteritis challenge(Zhongguo Xumu Shouyi Xuehui,Chinese Association of Animal Science and Veterinary Medicine, 2022); ; ; ; ;Ader, PeterThe present study investigated whether supplementing fibre-degrading enzymes can ameliorate the severity of subclinical necrotic enteritis (NE) in broiler chickens offered wheat- or maize-based diets. A total of 1,544 mixed-sex broiler chickens were assigned to 16 experimental treatments as a 2 x 2 x 4 factorial arrangement of treatments. The factors were the following: NE challenge, yes or no" diet type, wheat- or maize-based" and enzyme supplementation, control (no enzyme), family 10 xylanase (XYN10), family 11 xylanase (XYN11) or b-mannanase (MAN). Each treatment was replicated 6 times, with 16 birds per replicate pen. A three-way challenge x diet type x enzyme interaction occurred for body weight at 21 d of age (P ¼ 0.025) and overall feed conversion ratio (P ¼ 0.001). In the non-challenged birds fed the wheat-based diet, supplementing MAN increased d 21 body weight compared to the control. In challenged birds fed the maize-based diet, supplemental XYN11 impeded body weight and overall FCR compared to the control. Birds offered the maize-based diet presented heavier relative gizzard weights at both 16 and 21 d of age (P < 0.001) and reduced liveability (P ¼ 0.046) compared to those fed the wheatbased diet. Enzyme supplementation reduced ileal and jejunal digesta viscosity at 16 d of age only in birds fed the wheat-based diet (P < 0.001). XYN11 increased ileal digesta viscosity in birds fed the maizebased diet, and MAN reduced it in birds fed the wheat-based diet at 21 d of age (P ¼ 0.030). Supplementing XYN11 improved ileal soluble non-starch polysaccharides (NSP) digestibility in birds fed the wheat-based diet compared to non-supplemented birds (P < 0.001). Birds fed the wheat-based diet displayed a higher abundance of Bifidobacterium, Lactobacillus and Enterobacteriaceae and butyric acid in the caeca at 16 d of age compared to birds fed the maize-based diet (P < 0.05). In conclusion, supplemental XYN11 exacerbated the negative impact of NE on growth performance in birds fed the maize based diet. Supplementing wheat-based diets with fibre-degrading enzymes ameliorates production losses induced by NE.
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Journal ArticlePublication Phenotypic and genetic relationships for feed intake, feed efficiency, body composition and cow milk yield measured postweaning and in mature beef cowsContext. Providing feed is the largest cost in beef production. Genetic variation exists in feed efficiency traits in young cattle but the genetic associations with feed efficiency traits in cows are poorly understood, but if strong and favourable, they might be used to improve feed efficiency of cows. Aim. To examine the phenotypic and genetic relationships among feed intake, feed efficiency, body composition and cow milk yield measured in young cattle and in cows. Methods. Data on 1783 young Angus, Hereford, Polled Hereford and Shorthorn bulls and heifers, and for 751 of the females as cows, were used to calculate the phenotypic and genetic relationships among feed efficiency traits, body composition and cow milk yield measured postweaning and in mature cows. The young cattle were tested for feed intake and feed efficiency at approximately 9 months of age and the females, after two calvings, were tested again as non-pregnant, non-lactating cows at approximately 4 years of age. Key results. At the postweaning test, the heritability estimates for feed intake, average daily gain, test weight, residual feed intake (RFI), feed conversion ratio, rump fat depth and eye-muscle area were 0.47, 0.32, 0.46, 0.42, 0.28, 0.47 and 0.20 respectively. Corresponding heritability estimates in the cow test were 0.27, 0.35, 0.74, 0.22, 0.30, 0.47 and 0.12. Heritability estimates for 400-day weight, cow 4-year weight and cow milk yield were 0.47, 0.62 and 0.15 respectively. Genetic correlations between traits measured postweaning and the same traits measured in the cow were moderate to high, and for the feed efficiency trait, RFI, was very high (0.95), close to unity. Conclusions. Inclusion of postweaning RFI as a selection criterion in beef cattle breeding can be expected to lead to improvement in cow feed efficiency. Implications. Most breeding decisions in beef cattle are based on traits measured early in life and for replacement heifers are made with an aim to improve their productivity and profitability as cows. The strong and favourable associations measured between postweaning RFI and cow RFI mean that feed efficiency measured in young cattle can be used as a selection trait to improve cow feed efficiency.
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Publication Open AccessJournal ArticleSelection for growth rate at pasture in Angus cattle results in heavier cattle that eat more in the feedlotContext. Selection for growth rate has received considerable attention in beef cattle but the evidence for an improvement in the efficiency of feed conversion is equivocal. Aim. To examine whether feed efficiency by beef cattle finished in a feedlot had been changed in response to divergence selection for growth rate. Methods. The Angus cattle used came from three lines of cattle selected for over five generations for fast growth rate to yearling age (High-line), slow growth (Low-line), or from an unselected Control-line. Over sequential years, a cohort of steers, then of heifers and then of steers, representative of the lines, were measured for feedlot performance, and carcase- and meat-quality traits. The animals were fed a high-energy feedlot ration and after an adjustment period they underwent a performance test of at least 70 days of duration. After slaughter, muscle samples were taken for subsequent measurement of the components of the endogenous calpain proteolytic enzyme system. Their carcasses underwent a standard chiller assessment and meat samples were taken after 1 day and 14 days (steers) or 17 days (heifers) for objective measurement of tenderness. Key results. Cattle from the High-line grew 48% faster (P < 0.05), and ate 48% more feed (P < 0.05) than did those from the Low-line, but had similar (P > 0.05) feed conversion ratio and residual feed intake. There were no differences between the High-line and Low-line in the visual meat-quality attributes of meat colour, fat colour and marbling, and no differences in the objective measurements of tenderness and connective-tissue toughness. There was no evidence of a selection response in the circulating concentrations of the metabolites and hormones measured, nor in the endogenous calpain proteolytic enzyme system in muscle. Conclusions. The superior growth demonstrated by the High-line cattle over the feedlot test was accompanied by a higher feed intake, with no evidence for an improvement in feed efficiency. Implications. Selection for growth rate is a powerful tool to alter animal performance but the beef industry needs to be cognisant of the proportional increase in feed requirement from breeding bigger animals.
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Journal ArticlePublication Selection for residual feed intake affects appetite and body composition rather than energetic efficiencyResidual feed intake (RFI) is the difference between an animal's actual feed intake and that which would be expected based on production. This experiment was to test the hypothesis that part of the variation in RFI may be due to differences in energetic efficiency through changes in heat production, these being in part due to differences in protein metabolism. Following three generations of divergent selection for RFI, eight High and eight Low-RFI heifers were fed at both 105% and 180% of predicted maintenance feed requirements. Between-RFI line and feeding-level differences were assessed for energy intake, protein metabolism, heat production, body composition, energy and nitrogen balance and digestibility. The RFI lines did not differ in protein metabolism or heat production. The High-RFI heifers deposited 51% and 56% more subcutaneous fat at the P8 rump and 12/13th rib sites, respectively, with no difference in eye muscle area gain or average daily weight gain. The greater fat deposition of High-RFI heifers was due to a larger ad libitum feed consumption compared with the Low-RFI heifers. Energy and nitrogen balance did not differ between the RFI lines. The energy transactions indicated no difference in the efficiency of energy use on 105% maintenance, although when fed 180% of maintenance the differences in feed intake suggest variation in appetite as the mechanism contributing to RFI. All of the extra energy consumed by High-RFI heifers above maintenance and deposition of protein was associated with additional energy retained as fat. This study suggests that selection for RFI may not lead to improved efficiency of energy use.
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Journal ArticlePublication Selection for yearling growth rate in Angus cattle results in bigger cows that eat moreContext. Measurement of weight provides the basis of most performance-recording schemes for beef cattle around the world. The limitation of faster growth rate as a breeding objective, without considering changes in mature-cow weight, is the expected increase in cow size and, hence, feed requirements. Aims. To measure the correlated changes in feed intake and efficiency of cows, calves and the cow–calf unit following divergent selection for growth rate. Methods. The cows and their calves came from three lines of Angus cattle selected for either fast weight gain to yearling age (the High-line), slow weight gain (the Low-line), or from an unselected Control-line. Efficiency was evaluated over an annual production cycle. Individual cow weights and feed intakes, and calf growth and feed intake (including milk), were recorded. Milk production, milk composition and body composition were also measured so that correlated changes in efficiency of use of energy and nitrogen could be determined. Key results. The High-line cows were 18% (P < 0.05) heavier than the Low-line cows at the start and consumed 7% (P < 0.05) more feed than did the Low-line cows. Feed efficiency of the cow–calf unit was 12% higher (P < 0.05) in the High-line cows and calves than in the Low-line cows and calves. When compared on the basis of feed used relative to their weight and weight gain there was no difference (P > 0.05) between the selection lines. Divergent selection was accompanied by a change in body composition, with the High-line cows containing proportionally less protein and more fat in their bodies than did the Low-line cows. There was no evidence for change in the efficiency of feed energy use, but there was a 10% (P < 0.05) improvement in nitrogen efficiency of the cow–calf unit in the High-line compared with the Low-line. Conclusions. Divergent selection for weight gain led to a correlated change in cow size and cow feed requirements. Implications. This experiment supported the consensus among earlier reviews that there is little evidence that selection for growth rate or size, without moderating change in mature-cow weight, is associated with improved efficiency of feed energy use in maternal beef breeds.
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