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Variation in nutrition is a key determinant of growth, body composition, and the ability of animals to perform to their genetic potential. Depending on the quality of feed available, animals may be able to overcome negative effects of prior nutritional restriction, increasing intake and rates of tissue gain, but full compensation may not occur. A 2 × 3 × 4 factorial serial slaughter study was conducted to examine the effects of prior nutritional restriction, dietary energy density, and supplemental rumen undegradable protein (RUP) on intake, growth, and body composition of lambs. After an initial slaughter (n = 8), 124 4-mo-old Merino cross wethers (28.4 ± 1.8 kg) were assigned to either restricted (LO, 500 g/d) or unrestricted (HI, 1500 g/d) intake of lucerne and oat pellets. After 8 wk, eight lambs/group were slaughtered and tissue weights and chemical composition were measured. Remaining lambs were randomly assigned to a factorial combination of dietary energy density (7.8, 9.2, and 10.7 MJ/kg DM) and supplemental RUP (0, 30, 60, and 90 g/d) and fed ad libitum for a 12- to 13-wk experimental period before slaughter and analysis. By week 3 of the experimental period, lambs fed the same level of energy had similar DMI (g/d) and MEI (MJ/d) (P0.05), regardless of prior level of nutrition. Restricted-refed (LO) lambs had higher rates of fat and protein gain than HI lambs (P0.05) but had similar visceral masses (P0.05). However, LO lambs were lighter and leaner at slaughter, with proportionally larger rumens and livers (P0.05). Tissue masses increased with increasing dietary energy density, as did DMI, energy and nitrogen (N) retention (% intake), and rates of protein and fat gain (P0.05). The liver increased proportionally with increasing dietary energy density and RUP (P0.05), but rumen size decreased relative to the empty body as dietary energy density increased (P0.05) and did not respond to RUP (P0.05). Fat deposition was greatest in lambs fed 60 g/d supplemental RUP (P0.05). However, lambs fed 90 g/d were as lean as lambs that did not receive supplement (P0, P0.05), with poorer nitrogen retention and proportionally heavier livers than P0 lambs (P0.05). In general, visceral protein was the first tissue to respond to increased intake during refeeding, followed by non-visceral protein and fat, highlighting the influence of differences in tissue response over time on animal performance and body composition.Animal performance is determined by the combined effects of both prior and current nutrition. The present study used a 2 × 3 × 4 factorial to examine the effects of prior feeding level (HI or LO) on subsequent ad-libitum intake of diets varying in energy density (7.8, 9.2, 10.7 MJ/kg DM) and level of supplemental rumen undegradable protein (RUP; 0, 30, 60, and 90g/d). By week 3 of refeeding, LO and HI lambs had similar feed intake, but LO lambs had proportionally more gut and liver tissue and were lighter and leaner at final slaughter. As dietary energy density increased, the rumen became proportionally smaller while the liver became proportionally larger. Liver size increased with increasing RUP, and lambs fed 30 and 60 g/d were fatter than other lambs. However, lambs fed 90 g/d RUP had less fat than other lambs, as the increased energy requirements of a larger liver and of disposing of excess nitrogen appeared to outweigh any nutritional benefits. Understanding how prior nutrition affects current performance, as well as how tissues vary in their response to the same diet, is key to improving our understanding of animal performance and response to change.

Respiration chambers are considered the reference method for quantifying the daily CH production rate (MPR) and CO 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 CH and CO, 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 CH and CO records. Data on 495 Angus steers on a 70-d ad libitum feedlot diet with 46,657 CH and CO records and on 121 Angus heifers on a 15-d ad libitum roughage diet with 7,927 CH and CO 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 CH and CO, starting with 5 records and progressively increasing to a maximum of 80 records. For both CH and CO 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 (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 CH and CO 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 CH or CO 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.

Nitrate supplementation has been shown to be effective in reducing enteric methane emission from ruminants, but there have been few large-scale studies assessing the effects of level of nitrate supplementation on feed intake, animal growth, or carcass and meat quality attributes of beef cattle. A feedlot study was conducted to assess the effects of supplementing 0.25 or 0.45% NPN in dietary DM as either urea (Ur) or calcium nitrate (CaN) on DMI, ADG, G:F, and carcass attributes of feedlot steers ( = 383). The levels of NPN inclusion were selected as those at which nitrate has previously achieved measurable mitigation of enteric methane. The higher level of NPN inclusion reduced ADG as did replacement of Ur with CaN (0.01). A combined analysis of DMI for 139 steers with individual animal intake data and pen-average intakes for 244 bunk-fed steers showed a significant interaction between NPN source and level ( = 0.02) with steers on the high-CaN diet eating less than those on the other 3 diets (0.001). Neither level nor NPN source significantly affected cattle G:F. There was a tendency ( = 0.05) for nitrate-supplemented cattle to have a slower rate of eating (g DMI/min) than Ur-supplemented cattle. When adjusted for BW, neither NPN source nor inclusion level affected cross-sectional area of the LM or fatness measured on the live animal. Similarly, there were no significant main effects of treatments on dressing percentage or fat depth or muscling attributes of the carcass after adjustment for HCW (0.05). Analysis of composited meat samples showed no detectable nitrates or nitrosamines in raw or cooked meat, and the level of nitrate detected in meat from nitrate-supplemented cattle was no higher than for Ur-fed cattle (0.05). We conclude that increasing NPN inclusion from 0.25 to 0.45% NPN in dietary DM and replacing Ur with CaN decreased ADG in feedlot cattle without improving G:F.

Ruminants contribute up to 80% of greenhouse gas (GHG) emissions from livestock, and enteric methane production by ruminants is the main source of these GHG emissions. Hence, reducing enteric methane production is essential in any GHG emissions reduction strategy in livestock. Data from 2 performance-recording research herds of Angus cattle were used to evaluate a number of methane measures that target methane production (MPR) independent of feed intake and to examine their phenotypic relationships with growth and body composition. The data comprised 777 young bulls and heifers that were fed a roughage diet (ME of 9 MJ/kg DM) at 1.2 times their maintenance energy requirements and measured for MP in open circuit respiration chambers for 48 h. Methane traits evaluated included DMI during the methane measurement period, MPR, and methane yield (MY; MPR/DMI), with means (± SD) of 6.2 ± 1.4 kg/d, 187 ± 38 L/d, and 30.4 ± 3.5 L/kg, respectively. Four forms of residual MPR (RMP), which is a measure of actual minus predicted MPR, were evaluated. For the first 3 forms, predicted MPR was calculated using published equations. For the fourth (RMPR), predicted MPR was obtained by regression of MPR on DMI. Growth traits evaluated were BW at birth, weaning (200 d of age), yearling age (400 d of age), and 600 d of age, with means (± SD) of 34 ± 4.6, 238 ± 37, 357 ± 45, and 471 ± 53 kg, respectively. Body composition traits included ultrasound measures (600 d of age) of rib fat, rump fat, and eye muscle area, with means (± SD) of 3.8 ± 2.6 mm, 5.4 ± 3.8 mm, and 61 ± 7.7 cm(2), respectively. Methane production was positively correlated (r ± SE) with DMI (0.65 ± 0.02), MY (0.72 ± 0.02), the RMP traits (r from 0.65 to 0.79), the growth traits (r from 0.19 to 0.57), and the body composition traits (r from 0.13 to 0.29). Methane yield was, however, not correlated (r ± SE) with DMI (-0.02 ± 0.04) as well as the growth (r from -0.03 to 0.11) and body composition (r from 0.01 to 0.06) traits. All the RMP traits were strongly correlated to MY (r from 0.82 to 0.95). These results indicate that reducing MPR per se can have a negative impact on growth and body composition of cattle. Reducing MY, however, will likely have the effect of reducing MPR without impacting productivity. Where a ratio trait is undesirable, as in animal breeding, any of the RMP traits can be used instead of MY. However, where independence from DMI is desired, RMPR should be a trait worth considering.

A total of 2,600 methane (CH4) and 1,847 CO2 measurements of sheep housed for 1 h in portable accumulation chambers (PAC) were recorded at 5 sites from the Australian Sheep CRC Information Nucleus, which was set up to test leading young industry sires for an extensive range of current and novel production traits. The final validated dataset had 2,455 methane records from 2,279 animals, which were the progeny of 187 sires and 1,653 dams with 7,690 animals in the pedigree file. The protocol involved rounding up animals from pasture into a holding paddock before the first measurement on each day and then measuring in groups of up to 16 sheep over the course of the day. Methane emissions declined linearly (with different slopes for each site) with time since the sheep were drafted into the holding area. After log transformation, estimated repeatability (rpt) and heritability (h(2)) of liveweight-adjusted CH4 emissions averaged 25% and 11.7%, respectively, for a single 1-h measurement. Sire × site interactions were small and nonsignificant. Correlations between EBV for methane emissions and Sheep Genetics Australia EBV for production traits were used as approximations to genetic correlations. Apart from small positive correlations with weaning and yearling weights (r = 0.21-0.25, P0.05), there were no significant relationships between production trait and methane EBV (calculated from a model adjusting for liveweight by fitting separate slopes for each site). To improve accuracy, future protocols should use the mean of 2 (rpt = 39%, h(2) = 18.6%) or 3 (rpt = 48%, h(2) = 23.2%) PAC measurements. Repeat tests under different pasture conditions and time of year should also be considered, as well as protocols measuring animals directly off pasture instead of rounding them up in the morning. Reducing the time in the PAC from 1 h to 40 min would have a relatively small effect on overall accuracy and partly offset the additional time needed for more tests per animal. Field testing in PAC has the potential to provide accurate comparisons of animal and site methane emissions, with potentially lower cost/increased accuracy compared to alternatives such as SF6 tracers or open path lasers. If similar results are obtained from tests with different protocols/seasonal conditions, use of PAC measurements in a multitrait selection index with production traits could potentially reduce methane emissions from Australian sheep for the same production level.

Seventy-six Angus steers chosen from breeding lines divergently selected for residual feed intake (RFI) were studied to quantify the relationship between RFI and the daily rate of methane production (MPR). A 70-d feeding test using a barley-based ration was conducted in which the voluntary DMI, feeding characteristics, and BW of steers were monitored. The estimated breeding value (EBV) for RFI (RFI(EBV)) for each steer had been calculated from 70-d RFI tests conducted on its parents. Methane production rate (g/d) was measured on each steer using SF(6) as a tracer gas in a series of 10-d measurement periods. Daily DMI of steers was lower during the methane measurement period than when methane was not being measured (11.18 vs. 11.88 kg; P = 0.001). A significant relationship existed between MPR and RFI when RFI (RFI(15d)) was estimated over the 15 d when steers were harnessed for methane collection (MPR = 13.3 x RFI(15d) + 179; r(2) = 0.12; P = 0.01). Animals expressing lower RFI had lower daily MPR. The relationship established between MPR and RFI(15d) was used to calculate a reduction in daily methane emission of 13.38 g accompanied a 1 kg/d reduction in RFI(EBV) in cattle consuming ad libitum a diet of 12.1 MJ of ME/kg. The magnitude of this emission reduction was between that predicted on the basis of intake reduction alone (18 g x d(-1) x kg of DMI(-1)) and that predicted by a model incorporating steer midtest BW and level of intake relative to maintenance (5 g x d(-1) x kg of DMI(-1)). Comparison of data from steers exhibiting the greatest (n = 10) and lowest (n = 10) RFI(15d) showed the low RFI(15d) group to not only have lower MPR (P = 0.017) but also reduced methane cost of growth (by 41.2 g of CH(4)/kg of ADG; P = 0.09). Although the opportunity to abate livestock MPR by selection against RFI seems great, RFI explained only a small proportion of the observed variation in MPR. A genotype x nutrition interaction can be anticipated, and the MPR:RFI(EBV) relationship will need to be defined over a range of diet types to account for this.

Hereditary hemochromatosis (HH) results in increased iron absorption and subsequent deposition in tissue. This condition occurs predominantly in individuals of Northern European and Celtic origin with Ireland having one of the highest allele frequencies in the world. This study examines the hypothesis that homozygosity for either the C282Y or H63D mutations in the HFE gene may be associated with aseptic loosening following total hip arthroplasty (THA). Two groups of individuals were screened for the C282Y and H63D mutations associated with HH. Group 1 were individuals who had undergone primary hip arthroplasty and group 2 were individuals who had undergone revision hip arthroplasty for aseptic loosening. Exclusion criteria included rheumatoid or other inflammatory arthropathies and revision due to causes other than aseptic loosening. Significantly more patients in the revision THA group were homozygous for the C282Y genotype (P = 0.014). Aseptic loosening occurred earlier in these patients (P = 0.009), in particular in the patients who had clinical signs of hemochromatosis. No association was seen with the H63D mutation and revision THA. The incidence of HH in the group of primary THA patients was no higher than the background incidence. Patients who require primary THA and who are homozygous for the C282Y mutation have an increased risk of developing aseptic loosening, leading to revision THA. Moreover C282Y homozygosity appears to be associated with earlier aseptic loosening than in individuals without the C282Y mutation.