Genetic and environmental variation in methane emissions of sheep at pasture

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, P < 0.05), 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

Breeding Ruminants that Emit Less Methane – The Role of International Collaboration

Ruminants contribute to global greenhouse gas (GHG) emissions, principally as enteric methane (CH4) emissions. Direct selection for reduced CH4 emissions through combined selection for both low residual feed intake and methane yield could potentially provide a long term reduction in enteric methane production of 40-45%. If a methane-related trait were to be implemented by a livestock industry it will most likely be via genomic breeding values, which demand large numbers of measured animals in the reference population. Given the size of the reference population required for methane traits, it is imperative that wherever possible groups around the world collaborate on methodologies for measurement and collection of data. This has been the primary focus of the Animal Selection Genetics and Genomics Network (ASGGN) of the Livestock Research Group of the Global Research Alliance to reduce GHG emissions from agriculture

Effect of diet and physiological state on recycling of urea in Merino ewes

The recycling of urea to the rumen was studied in Merino ewes during differentp hysiologicals tates using radioactivet racers. The results showed that although the proportion of urea recycled differed, similar amounts were recycled in dry and pregnant sheep over a wide range of N intake. Urea recycling increased significantly during lactation on all diets when compared with non-lactatings heep.T hus, factors other than simple diffusion of urea control urea recycling in sheep although the control mechanisms remain undefined.Die hersirkulasiev an ureum na die grootpensi s ondersoekb y Merino ooie tydens verskillendef isiologieset oestanded eur gebruik te maak van radio-aktiewem erkers.D ie resultatet oon dat hoewel die verhoudingu reum wat gehersirkuleeirs , verskil, is dieselfdeh oeveelhedeg ehersirkuleeirn dro€ en dragtige skape oor 'n wye reeksv an N inname.H ersirkulasiev an ureum het betekenisvotl oegeneemt ydens laktasieo p alle di€te, in vergelykingm et nie-lakterendes kape.D aar is dus ander faktore as eenvoudiged iffusie van ureum wat die hersirkulasiev an ureum in skape beheer, alhoewel die beheermeganismes ongedefinieerb ly.Keywords: Urea entry, urea recycling, pregnancy, lactation, ewes, nitrogen intak

Growth, development and nutritional manipulation of marbling in cattle: a review

This review describes the pattern of intramuscular fat accretion in cattle and the potential for its manipulation during both the pasture (or backgrounding) and intensive grain-finishing phases of development. A growth curve for the development of marbling in British and Japanese Black type breeds is discussed with the conclusion that 3 phases of development exist: (i) a period of growth up to ∼200 kg hot carcass weight where intramuscular fat does not increase; (ii) a period of linear development as carcass weight increases from 200 to 450 kg; and (iii) the attainment of mature body size (∼500 kg carcass weight depending on genotype) at which intramuscular fat content appears to reachea maximum. Data are also presented to show that the intramuscular and other fat depots develop at similar rates indicating that intramuscular fat is not a late maturing depot. Pre-finishing growth checks reduce the initial intramuscular fat at the start of finishing and this is translated into lower levels at the end of finishing. It is argued that the greatest potential for the manipulation of intramuscular fat accretion during fattening is via an increase in the net energy of the ration. Increasing net energy can be achieved by increasing the cereal grain content of the diet (grain v. grass); by feeding processed cereal grain, which allows both maximal rumen fermentation and small intestinal digestion of starch, and by increasing the lipid content of the diet. In addition it is proposed that the substrate supply or hormonal milieu can also be optimised, along with the availability of net energy to maximise fat accretion. The role of lipolysis (fat turnover) as a regulator of fat accretion is also discussed

Growth, development and nutritional development of marbling in cattle

This review discusses our current understanding of the growth and development of intramuscular fat and proposes a simple growth model to explain the accumulation of intramuscular fat in cattle. Potential effects of nutritional manipulation are discussed in relation to the proposed growth curve for intramuscular fat. The scope for nutritional control during both the pasture (or backgrounding) and intensive grain finishing phase are discussed. Additional discussion on nutritional triggers of the cellular and early life events associated with the development of the intramuscular fat are discussed in the companion paper by Harper and Pethick (2001)