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Journal ArticlePublication Associations of digestibility with phenotypic and genetic variation in methane production in Angus cattle(CSIRO Publishing, 2022-09-12) ;Smith, H C; ;Donoghue, K A ;Bird-Gardiner, T ;Arthur, P FContext: Cattle and sheep emit methane, a potent greenhouse gas, as part of the fermentation process of feed digestion in their gut; however, the mechanisms explaining differences among animals in enteric methane production are not fully understood. Aim: To investigate whether variation among animals in their ability to digest their test ration was associated with phenotypic and genetic variation in methane production. Methods: The experiment used 135 Angus beef cattle measured for their phenotypic and genetic merit for methane production. The extent of digestion of the dry matter (DMD) in the test ration by individual cattle was determined using silica as a naturally present indigestible marker. Its concentration in feed consumed and faeces was determined using rapid portable X-ray fluorescence spectroscopy, from which DMD was calculated. Key results: Higher daily methane-production rate (MPR), higher methane produced per unit of feed consumed (methane yield; MY) and higher methane produced than the predicted daily production (residual MPR; RMP) by animals was accompanied by higher DMD. Higher genetic merit for MPR was also accompanied by higher DMD, but DMD had no detectable association with genetic variation in the other two methane emission traits. The regression coefficients for change in MPR (g/day), MY (g/kg DMI), RMP (g/day) with change in DMD (%) were 2.6 ± 1.1 (s.e.; P < 0.05), 0.14 ± 0.07 (P < 0.1) and 0.68 ± 0.38 (P < 0.1) respectively. Conclusions: Differences among animals in their DMD were found and were associated with phenotypic variation in the three methane emission traits studied, and with genetic variation in daily methane production. The results support the caution that feeding and breeding interventions seeking to reduce methane emissions can also reduce the extent of digestion of feed by cattle. Implications: Feeding and breeding interventions that seek to reduce methane emissions may change rumen physiology and reduce the extent of digestion of feed by cattle, which may be undesirable.
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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 variance and covariance components for carbon dioxide production and postweaning traits in Angus cattle(American Society of Animal Science, 2020-08-10) ;Donoghue, Kath A; ; ; Arthur, Paul FThis experiment investigated phenotypic and genetic relationships between carbon dioxide production, methane emission, feed intake, and postweaning traits in Angus cattle. Respiration chamber data on 1096 young bulls and heifers from 2 performance recording research herds of Angus cattle were analyzed to provide phenotypic and genetic parameters for carbon dioxide production rate (CPR; n = 425, mean 3,010 +/- SD 589 g/d) and methane production rate (MPR; n = 1,096, mean 132.8 +/- SD 25.2 g/d) and their relationships with dry matter intake (DMI; n = 1,096, mean 6.15 +/- SD 1.33 kg/d), body weight (BW) and body composition traits. Heritability estimates were moderate to high for CPR (0.53 [SE 0.17]), MPR (0.31 [SE 0.07]), DMI (0.49 [SE 0.08]), yearling BW (0.46 [SE 0.08]), and scanned rib fat depth (0.42 [SE 0.07]). There was a strong phenotypic (0.83 [SE 0.02]) and genetic (0.75 [SE 0.10]) correlation between CPR and MPR. The correlations obtained for DMI with CPR and with MPR were high, both phenotypically (r(p)) and genetically (r(g)) (r(p): 0.85 [SE 0.01] and 0.71 [SE 0.02]; r(g) (0.95 [SE 0.03] and 0.83 [SE 0.05], respectively). Yearling BW was strongly correlated phenotypically (r(p) >= 0.60) and genetically (r(g) > 0.80) with CPR, MPR, and DMI, whereas scanned rib fat was weakly correlated phenotypically (r(p) < 0.20) and genetically (r(g) <= 0.20) with CPR, MPR, and DMI. The strong correlation between both CPR and MPR with DMI confirms their potential use as proxies for DMI in situations where direct DMI recording is not possible such as on pasture.
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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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Journal ArticlePublication Optimizing test procedures for estimating daily methane and carbon dioxide emissions in cattle using short-term breath measures(Oxford University Press, 2017-02) ;Arthur, P F ;Barchia, I M ;Weber, C; ;Donoghue, K A; Respiration chambers are considered the reference method for quantifying the daily CH4 production rate (MPR) and CO2 production rate (CPR) of cattle" however, they are expensive, labor intensive, cannot be used in the production environment, and can be used to assess only a limited number of animals. Alternative methods are now available, including those that provide multiple short-term measures of CH4 and CO2, such as the GreenFeed Emission Monitoring (GEM) system. This study was conducted to provide information for optimizing test procedures for estimating MPR and CPR of cattle from multiple short-term CH4 and CO2 records. Data on 495 Angus steers on a 70-d ad libitum feedlot diet with 46,657 CH4 and CO2 records and on 121 Angus heifers on a 15-d ad libitum roughage diet with 7,927 CH4 and CO2 records were used. Mean (SD) age and BW were 554 d (SD 92) and 506 kg (SD 73), respectively, for the steers and 372 d (SD 28) and 348 kg (SD 37), respectively, for the heifers. The 2 data sets were analyzed separately but using the same procedures to examine the reduction in variance as more records are added and to evaluate the level of precision with 2 vs. 3 min as the minimum GEM visit duration for a valid record. The moving averages procedure as well as the repeated measures procedure were used to calculate variances for both CH4 and CO2, starting with 5 records and progressively increasing to a maximum of 80 records. For both CH4 and CO2 and in both data sets, there was a sharp reduction in the variances obtained by both procedures as more records were added. However, there was no substantial reduction in the variance after 30 records had been added. Inclusion of records with a minimum of 2-min GEM visit duration resulted in reduction in precision relative to a minimum of 3 min, as indicated by significantly (P < 0.05) more heterogeneous variances for all cases except CH4 in steers. In addition, more records were required to achieve the same level of precision relative to data with minimum GEM visit durations of 3 min. For example, in the steers, 72% reduction in initial variance was achieved with 30 records for both CH4 and CO2 when minimum GEM visit duration was 3 min, relative to 45 records when data with a minimum visit duration of 2 min were included. It is concluded from this study that when using records of multiple short-term breath measures of CH4 or CO2 for the computation of an animal's MPR or CPR, a minimum of 30 records, each record obtained from a minimum GEM visit duration of 3 min, are required.
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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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Journal ArticlePublication Selection for increased visual muscling increases carcass leanness without compromising predicted Meat Standards Australia eating-quality indexContext. Selection using visual muscle score (MS) has been proposed to increase carcass leanness (i.e. meat yield), without compromising eating quality.
Aims. The aim of the present study was to examine the impact that selection for divergent MS has on live animal, commercial carcass and carcass tissue weights by using computed tomography (CT) including Meat Standards Australia (MSA) index-predicted eating quality.
Methods. Data from 67 steers originating from three muscling lines, namely, low, high and heterozygous high (HighHet – heterozygous for the 821 del11 myostatin mutation), were used. Visual MS was assessed on all steers. All steers were slaughtered and the left-hand side of each carcass was processed with fat trimming limited to only that required for hygiene purposes and kidney fat was not removed. All carcasses were MSA graded and then boned-out into untrimmed boneless primals (e.g. rump, cube roll). A CT scan of each beef primal was processed with image analysis software to estimate lean and fat tissue weights. The following traits were analysed: MS, weaning and slaughter weights" commercial carcass traits, including cold carcass weight, rump fat, MSA rib fat, MSA eye-muscle area, MSA marble score and MSA index" and CT-scanned compositional carcass traits, including lean, fat and bone tissues (%) and lean : bone ratio. All data were analysed with a linear mixed-effects model using REML. Least-squares means for the three muscling lines are reported. Linear trends between MS and seven carcass traits, with and without the myostatin mutation, are presented graphically.
Key results. Muscling line effects (P < 0.05) were found for visual MS and carcass traits. Linear trends between MS and carcass traits with and without the myostatin mutation demonstrate that increases in MS (P = 0.24) did not compromise predictions of MSA index even though MSA marble score decreased (P = 0.026), but myostatin decreased MSA marble score and tended to decrease MSA index (P = 0.097). Increases in the MSA eye-muscle area were associated with increases in MS (P < 0.01), with little effect of myostatin. Increases in MS and the myostatin mutation were both associated with increases (P < 0.01) in lean tissue (%) and the lean : bone ratio, and decreases (P = 0.02) in fat tissue (%).
Conclusions. The results indicate selection for high MS can be used to increase carcass yield, without negatively affecting MSA index predictions of eating quality.
Implications. Producers can use MS to identify animals with higher yields to increase carcass leanness and decrease carcass waste fat, without compromising MSA index predictions of eating quality, but should do so while considering all traits that affect profitability, in particular marble score and its association with eating quality.
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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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