Predicting metabolisable energy intake by free-ranging cattle using multiple short-term breath samples and applied to a pasture case-study
Context: Research into improving feed efficiency by ruminant animals grazing pastures has historically been restrained by an inability to measure feed intake by large numbers of individual animals. Recent advances in portable breath measurement technology could be useful for this purpose but methodologies need to be developed.
Aims: To evaluate predictive models for metabolisable energy intake (MEI) by free-ranging cattle using multiple short-term breath samples and then apply these to predict MEI by free-ranging cattle in a historic grazing experiment with cattle genetically divergent for residual feed intake (feed efficiency).
Methods: Predictive models for MEI were developed using bodyweight (BW) data, and carbon dioxide production rate (CPR) and methane production rate (MPR) from multiple short-term breath measurements, from an experiment with long-fed Angus steers on a grain-based diet, and an experiment with short-fed Angus heifers on a roughage diet. Heat production was calculated using CPR and MPR. Energy retained (ER) in body tissue gain by steers was calculated from BW, ADG, initial and final subcutaneous fat depths, and for both groups using feeding-standards equations.
Key results: Metabolic mid-test BW (MBW) explained 49 and 47% of the variation in MEI in the steer and heifer experiment, respectively, and for the steers adding ADG and then subcutaneous fat gain resulted in the models accounting for 60 and then 65% of the variation in MEI. In the steer experiment, MBW with CPR explained 57% of the variation in MEI, and including MPR did not account for any additional variation. In the heifer experiment, MBW with CPR explained 50%, and with MPR accounted for 52% of the variation in MEI. Heat production plus ER explained 60, 35 and 85% of the variation in MEI in the steer and the heifer experiments, and in the pooled data from both experiments, respectively.
Conclusions: Multiple short-term breath measurements, together simple BW data, can be used to predict MEI by free-ranging cattle in studies in which animals do not have feed-intake or ADG recorded.
Implications: This methodology can be used for research into improving feed efficiency by farm animals grazing pastures.
Associations among methane emission traits measured in the feedlot and in respiration chambers in Angus cattle bred to vary in feed efficiency
The objective of the study was to evaluate associations among animal performance and methane emission traits under feedlot conditions and in respiration chambers in Angus cattle bred to vary in residual feed intake (RFI), which is a measure of feed efficiency. Fifty-nine cattle were tested for feedlot RFI, of which 41 had methane production recorded on an ad libitum grain-based ration in the feedlot, 59 on a restricted grain-based ration in respiration chambers, and 57 on a restricted roughage ration in respiration chambers. The cattle became older and heavier as they went through the different phases of the experiment, but their feed intake (expressed as DMI) and daily emission of enteric methane (methane production rate; MPR) did not increase proportionally, as feed offered was restricted in the respiration chamber tests. Methane emissions by individual animals relative to their DMI were calculated as methane yield (MY; MPR/DMI) and as 2 measures of residual methane production (RMPJ and RMPR), which were calculated as the difference between measured MPR and that predicted from feed intake by 2 different equations. Within each test regime, MPR was positively correlated (r = 0.28 to 0.61) with DMI. Phenotypic correlations for MY, RMPJ, and RMPR between the feedlot test and the restricted grain test (r = 0.40 to 0.43) and between the restricted grain test and the restricted roughage test were moderate (r = 0.36 to 0.41) and moderate to strong between the feedlot test and the restricted roughage test (r = 0.54 to 0.58). These results indicate that the rankings of animals for methane production relative to feed consumed are relatively stable over the 3 test phases. Feedlot feed conversion ratio and RFI were not correlated with MPR in the feedlot test and grain-based chamber test but were negatively correlated with MPR in the chamber roughage test (r = -0.31 and -0.37). Both were negatively correlated with MY and RMPJ in the feedlot test (r = -0.42 to -0.54) and subsequent chamber roughage test (r = -0.27 to -0.49). Midparent estimated breeding values for RFI tended to be negatively correlated with MY and RMPJ in the feedlot test (r = -0.27 and -0.27) and were negatively correlated with MY, RMPJ, and RMPR in the chamber roughage test (r = -0.33 to -0.36). These results showed that in young growing cattle, lower RFI was associated with higher MY, RMPJ, and RMPR but had no significant association with MPR.
Associations of digestibility with phenotypic and genetic variation in methane production in Angus cattle
Context: 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.
Measures of methane production and their phenotypic relationships with dry matter intake, growth, and body composition traits in beef cattle
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 cm2, 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.
Divergent Selection for Methane Yield in Beef Cattle
Genetic selection and breeding to reduce methane production is one option to reduce greenhouse gas emissions, but correlated responses in production traits also need to be considered. The objective of this study was to quantify the effect of divergent selection for methane yield (MY), on methane and body weight traits in Angus cattle. High and Low MY selection lines were created in each of two performance-recorded Angus research herds during the 2011 mating season. This study is a preliminary report on the divergence of these selection lines, as assessed by the performance of the 2013 born progeny. There was no significant selection line by herd interaction. Approximately half a generation of selection was achieved. There was a significant (P<0.05) divergence between the two lines in the selected trait, methane yield. This was also reflected in the significant (P<0.05) selection line differences in the residual methane (actual minus expected methane production) traits and also in the estimated breeding values for these traits. There were no significant selection line differences in birth, weaning and yearling weights.
Proxies to adjust methane production rate of beef cattle when the quantity of feed consumed is unknown
The aim of the present experiment was to evaluate the utility of carbon dioxide production rate (CPR; g CO₂/ day) and animal weight (WT) data as proxies for feed intake to adjust methane production rate (MPR; g CH₄/day) in situations where dry-matter intake (DMI) is not known. This experiment measured individual-animal DMI, MPR and CPR in the feedlot, and then again on restricted quantities of grain and roughage diets in open-circuit respiration chambers. Of the 59 cattle tested in the feedlot, 41 had MPR and CPR recorded, and 59 and 57 had test results on the restricted grain and roughage rations. Methane production relative to DMI by individual animals was calculated as CH₄ yield (MY; MPR/ DMI) and as residual CH₄ production (RMPDMI; calculated as MPR less predicted MPR based on DMI). A second form of RMP: RMPCO₂ , was calculated by regressing MPR against CPR to determine whether animals were producing more or less CH₄ than predicted for their CPR. Carbon dioxide production rate was positively associated with DMI in all three test phases (R2 = 0.25, 0.45 and 0.47; all P < 0.001). The associations for MY with MPR : CPR were moderate and positive, as follows: R2 = 0.49 in the feedlot test; R2 = 0.37 in the restricted-grain test; and R2 = 0.59 in the restricted-roughage test, and with RMPCO₂ , values of R2 were 0.57, 0.34 and 0.59 in the three test phases (all P < 0.001). The R2 for RMPDMI with MPR : CPR in all three tests were 0.50, 0.79 and 0.69, and with RMPCO₂ , values of R2 were 0.68, 0.79 and 0.68 (all P < 0.001). The high R2 for MY with MPR : CPR and RMPCO2 and even higher R2 for RMPDMI with MPR : CPR and RMPCO₂ in all three test phases showed that CPR can be used to adjust MPR data for DMI when DMI is not recorded. In the feedlot test, where animal WT data were recorded over 70 days, MPR adjusted for WT and WT gain had R2 with MY and RMPDMI of 0.60 and 0.83, respectively (P < 0.001), offering the possibility that animal WT data determined over an extended time period could also be used as a proxy for DMI in adjustment of MPR.
Natural Variation in Methane Emissions among Progeny of Angus Bulls
Ruminants emit methane, a potent greenhouse gas, as a by-product of microbial fermentation of plant material in their rumen. The objective of this study was to investigate the existence of natural genetic variation in methane yield (methane production per unit feed intake) among beef cattle in Australia. Two pedigreed, performance-recording research herds of Angus cattle were used. Methane production (MP) was measured on individual yearling-age cattle in two animal houses in different years. Each animal had MP measured while being fed a fixe d daily allowance of a roughage diet of approximately 9 MJ ME/kg dry matter (DM). The amount offered was calculated to provide 1.2-times the estimated energy requirement for maintenance based on the animal's bodyweight. In 2010, MP was measured using the SF6 tracer dilution method, while in 2011 MP was measured in individual-animal respiratory chambers. A total of 339 cattle comprising 62 bulls and 73 heifers in 2010, and 139 bulls and 65 heifers in 2011, were assessed for MP. Methane yield was calculated as MP per unit dry matter intake (DMI). There was variation in both traits, with an almost 3-fold range in methane yield being observed. Phenotypically, MP was moderately correlated with DMI (r = 0.33) and with animal bodyweight (r = 0.40). In contrast, the phenotypic correlation of methane yield with DMI (r = -0.26) and with animal bodyweight (r = -0.15) were negative and weak. There was a large range in the mean for methane yield by progeny of the sires of the cattle tested. Compared to the sires whose progeny had the lowest average methane yield, there were sires whose progeny had average methane yield that were 24%, 24%, 16%, 19% and 11% higher across the five groups of cattle tested. This study has provided preliminary evidence that naturally occurring genetic variation exists in methane yield in cattle.
Effect of measurement duration in respiration chambers on methane traits of beef cattle
Records on 1043 young Angus heifer and bull progeny from 73 sires, measured for methane production in respiration chambers, were used to evaluate the accuracy of a 1-day measurement relative to 2-day measurement duration. The traits assessed were dry matter intake (DMI, kg/day), methane-production rate (MPR, g/day), methane yield (MY, MPR per unit DMI) and four residual methane (RMP, g/day) traits. The RMP traits were computed as actual MPR minus expected MPR, where the expected MPR were calculated from three widely used equations. The expected MPR for the fourth RMP trait was computed by regressing MPR on DMI, using the data from the study. Variance components, heritability, phenotypic and genetic correlations, and the efficiency of selection using 1-day compared with 2-day measurement were used as assessment criteria. The environmental variance for the 2-day measurement was slightly lower than that of the 1-day measurement for all the traits studied, indicating that the addition of an extra day of data was effective in reducing the amount of unexplained variation in each trait. However, these minor reductions did not have a major impact on accuracy; hence, very high phenotypic (rp of 0.91-0.99) and genetic (rg of 0.99 for each trait) correlations were obtained between the two measurement durations. The very high genetic correlation between the two durations of measurement indicated that, at the genetic level, the 1-day duration is measuring the same trait as the 2-day measurement duration. Any enteric-methane emission-abatement strategy that seeks to reduce MPR per se, may have a detrimental impact on ruminant productivity through a correlated reduction in feed intake; hence, MY and the RMP traits are likely to be the traits of interest for genetic improvement. Efficiency of selection for MY and the RMP traits ranged from 0.96 to 0.99, which implies that there would be less than 5% loss in efficiency by adopting a 1-day relative to a 2-day methane-measurement duration. While the throughput of the respiration-chamber facility can be increased by adopting a 1-day measurement duration, additional resources, such as holding pens, would be required to take advantage of the extra day.
Genetic Parameters for Methane Production and Relationships with Production Traits in Australian Beef Cattle
This paper reports heritability estimates for methane traits and genetic relationships with production traits in beef cattle. Traits recorded during the methane test period included dry matter intake (DMI), test liveweight (TWT), methane production (MPR) and methane yield (MY; MPR/DMI). Two methods of calculating residual methane traits (RMP) were evaluated. Production traits included birth (BWT), weaning (WWT), yearling (YWT) and final (FWT) liveweight. Heritabilities for MPR, MY and RMP traits were moderate (0.19 to 0.27), indicating that there is potential to use genetic improvement to reduce methane emissions in Australian beef cattle. MPR was moderately genetically correlated with MY (0.50) and RMP traits (0.50 to 0.63). However, MPR was also moderately to highly genetically correlated (0.36 to 0.86) with weight traits. Methane yield and RMP traits, however, were lowly to moderately genetically correlated (-0.06 to 0.45) with weight traits. These results indicate that selection for lower MPR would have a negative impact on growth in beef cattle. Selection for reduced MY or RMP, however, would lead to reduced MPR with minimal impact on animal productivity. The use of a ratio trait, like MY, in animal breeding is generally undesirable, thus selection on RMP traits is a better alternative.
Breeding Angus cattle that naturally emit less methane
The aim of this experiment is to investigate and demonstrate genetic variation in daily methane production (MP; g/d), methane intensity (MI; MP per unit bodyweight; g/kg) and methane yield (MY; MP per unit feed intake; g/kg). Angus cows in pedigree- and performance-recorded research herds at Industry & Investment NSW research centres at Grafton and Trangie NSW were mated in 2007 to Angus bulls that had previously been recorded for MY. Bulls that had been identified as either phenotypically high or low for MY were used as sires in the Grafton herd; unselected sires were used in the Trangie herd. In 2010 the near 2-year-old bull progeny from Trangie and heifer progeny from Grafton were measured for MP, MI and MY. There were 8 sires with progeny represented in the Trangie bull data (n=63 progeny). A wide range in least-squares (LS) sire means was observed for MP (191g/d to 233g/d), MI (0.26g/kg to 0.63g/kg) and MY (24.3g/kg to 30.2g/kg). There were 6 sires with progeny represented in the Grafton heifer data (n=79 progeny). A wide range in LS sire means was observed for MP (133g/d to 165g/d), MP (0.15g/kg to 0.55g/kg) and MY (21.5g/kg to 27.0g/kg). The differences between sires for these traits that indicate that there may be genetic variation present and provide preliminary evidence that selection on a methane production trait may be possible.