Low-methane yield sheep have smaller rumens and shorter rumen retention time

Abstract

In the present study, following the measurement of methane emissions from 160 mature ewes three times, a subset of twenty ewes was selected for further emission and physiological studies. Ewes were selected on the basis of methane yield (MY; g CH 4 /kg DM intake) being low (Low MY: .1 SD below the mean; n 10) or high (High MY: .1 SD above the mean; n 10) when fed a blended chaff ration at a fixed feeding level (1·2-fold maintenance energy requirements). The difference between the Low-and High-MY groups observed at the time of selection was maintained (P¼ 0·001) when remeasured 1 -7 months later during digesta kinetics studies. Low MY was associated with a shorter mean retention time of particulate (P, 0·01) and liquid (P,0·001) digesta, less amounts of rumen particulate contents (P, 0·01) and a smaller rumen volume (P,0·05), but not apparent DM digestibility (P¼ 0·27) or urinary allantoin excretion (P¼0·89). Computer tomography scanning of the sheep's rumens after an overnight fast revealed a trend towards the Low-MY sheep having more clearly demarcated rumen gas and liquid phases (P¼ 0·10). These findings indicate that the selection of ruminants for low MY may have important consequences for an animal's nutritional physiology.Key words: Greenhouse gas abatement: Enteric methane: Rumen retention time Australia and other countries are devoting considerable resources to the abatement of enteric methane production by livestock. In the predominantly extensive pastoral production systems of Australia, the most practicable strategy may be that of exploiting observed differences in methane production within the ruminant populations (1 -3) through selective breeding. Lower methane yields (MY; g CH 4 /kg DM intake (DMI)) may arise due to one or more of the following factors: fermentation of less amounts of organic matter in the rumen; a shift in volatile fatty acid production towards alternative H þ -utilising (propionate or reductive acetogenesis) pathways; an increase in the relative yield of microbial cells produced by fermentation (4) , which may potentially be affected by host-derived differences in rumen morphology and function.Variation in the mean retention time (MRT) of rumen digesta affects the extent of degradation of organic matter in the rumen and the flow of undegraded microbial matter postruminally (5) , and MRT has been implicated as a basis for between-animal differences in wool production (6) . It has also been demonstrated that alterations in retention time can cause marked differences in the efficiency of microbial synthesis in vitro (7) , while more recently, in vivo studies have suggested that up to 40 % of the observed variation in methane production in sheep could be attributed to differences in mean rumen outflow (8) . As such, we hypothesised that MRT may contribute to between-animal differences in methane production among animals fed a constant diet. To test the hypothesis that differences in MY would be reflected in measurable differences in the rumen environment, MY together with the ...

Methane yield phenotypes linked to differential gene expression in the sheep rumen microbiome

“…Particle retention time in ruminants is known to be a heritable trait (Orskov et al 1988;Smuts et al 1995) and may explain at least some of the CH 4 yield variation observed in sheep (Pinares-Patiño et al 2003). Recently, CH 4 yield in sheep in Australia has been directly correlated with the retention time of feed particles and liquid and with the total amount of feed particles and rumen volume (Goopy et al 2013), further supporting this view.…”

Invited review: Large-scale indirect measurements for enteric methane emissions in dairy cattle: A review of proxies and their potential for use in management and breeding decisions

“…Although gene-centric metagenomics is not low cost or high throughput, these results point to potential future proxy approaches using inexpensive gene chips. 5 the size of the rumen and its retention time are related to CH 4 emission (Pinares Patiño et al, 2003;Barnett et al, 2012;Goopy et al, 2014). Rumen volume was determined by X-ray computed tomography scanning in the study by Goopy et al (2014), which demonstrated that low-MeY sheep had smaller rumens.…”

“…5 the size of the rumen and its retention time are related to CH 4 emission (Pinares Patiño et al, 2003;Barnett et al, 2012;Goopy et al, 2014). Rumen volume was determined by X-ray computed tomography scanning in the study by Goopy et al (2014), which demonstrated that low-MeY sheep had smaller rumens. The rumen content morphology score also tended to differ between the groups, suggesting that there may be a structural difference in the relationship among the solid, liquid, and air phases of the rumen contents between highand low-CH 4 -emitting sheep.…”

“…The rumen content morphology score also tended to differ between the groups, suggesting that there may be a structural difference in the relationship among the solid, liquid, and air phases of the rumen contents between highand low-CH 4 -emitting sheep. Faster passage of material from the rumen results in a reduction in the time available to ferment substrate (Goopy et al, 2014). The differences recorded by Goopy et al (2014) may be related to feeding the sheep at a fixed energy requirement level, and those authors proposed that the work should be repeated with animals fed ad libitum.…”

“…Faster passage of material from the rumen results in a reduction in the time available to ferment substrate (Goopy et al, 2014). The differences recorded by Goopy et al (2014) may be related to feeding the sheep at a fixed energy requirement level, and those authors proposed that the work should be repeated with animals fed ad libitum. Apparent totaltract digestibility did not differ between high-and low-MeY groups in that study, suggesting potential for postruminal digestion to compensate for reductions in rumen fermentation.…”