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Improving production efficiency and reducing methane emissions in meat and wool sheep

Sheep and cattle produce 60-70% of agricultural greenhouse gas emissions in Australia, and these gases are predominantly methane from rumen fermentation. Reducing methane emissions from livestock is an emerging issue for agriculture and livestock production. Of the possible options to mitigate methane emissions exploiting the differences in methane production between individual animals through genetic selection appears to be the most likely strategy that could be adopted in extensive grazing systems. Development of robust protocols to measure a methane phenotype on large numbers of animals is a first step to towards establishing the feasibility of reducing methane emissions by genetic selection. This is a progress report that summarises the first phase of a larger project. The work reported here was undertaken in NSW and WA and specifically aimed to establish relationships between feed intake, proxies for feed intake and methane production from ewes fed different diets and across different physiological states.

In NSW methane production from about 100 ewes from four sires selected for extremes in methane production was measured several times using respiration chambers and or portable accumulation chambers. The measurements were completed when dry ewe were fed indoors a forage based diet either ad libitum or at maintenance or when they grazed different pastures, plus when fed ad-libitum and 1.6 x maintenance (calculated for dry ewes, approximately maintenance for pregnant ewes) indoors during late pregnancy. Where possible intakes were measured plus detailed measurements of oxygen and carbon dioxide concentrations. The ewes were CT scanned to characterise the reticulo-rumen complex and rumen fluid samples collected to quantify VFA’s. In WA, almost 400 ewe lambs were measured for feed intake and methane production post-weaning when fed pellets ad libitum indoors. They were then mated as ewe lambs and methane production was again measured when they were grazing green pasture when the ewes were pregnant or dry.

Methane production varied by almost 2-fold across diets but the effects of pregnancy status on methane production was relatively small. At the NSW site there was a small negative effect of pregnancy status on methane production rate measured in respiration chambers after adjustment for feed intake and live weight. This effects was also evident at the WA site and methane production adjusted for live weight was 8% lower in pregnant than dry ewes. A reduction in methane production rate would be anticipated during pregnancy if there is a concomitant decrease in retention time of digesta in the rumen. The reduction in methane after adjustment for live weight could also reflect that the live weights used included the weight of the conceptus, which was probably about 10% of live weight given measurements were completed around day 125 of pregnancy. In any case, although there may be a reduction in methane production rate with pregnancy status, the magnitude of the effect was such that at present there is no case for adjusting the inventory to account for it. There was no significant interaction between sire and pregnancy status or reproductive rate at either site, which suggests that differences between sire groups was maintained across physiological states.

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This page was last updated on 25/07/2017

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