Correlations between feed intake, residual feed intake and methane emissions in Maternal Composite ewes at post weaning, hogget and adult ages

Sheep production in southern Australia (particularly south west Victoria) is based increasingly on the Maternal Composite ewe, a self-replacing stable crossbred. Breeding programs have focussed on maternal traits such as reproduction and lamb growth. Understanding the variability, range and correlations between the traits of residual feed intake (RFI), feed intake (dry matter intake, DMI), growth rate and methane (CH4) emissions within the Maternal Composite ewe flock is essential to development of selection parameters that improve feed efficiency and reduce environmental impact. Sheep and cattle with low RFI (more efficient) have been observed to produce less CH4 than animals with high RFI. Selecting for animals with improved RFI may enable producers to improve the enterprise productivity while decreasing greenhouse gas emissions. Using automated feeders, feed intake, liveweight and growth rate of Maternal Composite ewes (n = 505) at three different ages (post-weaning, hogget and adult) were measured over 42 days and used to estimate residual feed intake (RFI) as a measure of feed efficiency. Methane emissions were determined twice during each RFI test period via portable accumulation chambers (PACs). During the feed intake test period, ewes were allowed ad libitum access to feed and their liveweight was recorded 3 times weekly. Daily dry matter intake varied by up to 2.1 kg DM/day between animals. Residual feed intake was phenotypically strongly correlated with DMI for all birth year and age group combinations. Within age groups, there were significant phenotypic correlations between measured traits (DMI, growth rate, RFI and CH4 emissions). However, these observed phenotypic relationships were not consistent at post-weaning, hogget or adult ages. Apart from one age by birth year combination, the relationship between CH4 emissions and RFI was not significant. This data suggests that there is enough variation in the Maternal Composite population for selection based on RFI to improve feed efficiency however, there was insufficient evidence of correlations between RFI and CH4 emissions to determine conclusively if improvements in RFI would also reduce CH4 emissions. The strong, consistent correlations between DMI and RFI suggest that a short-term measure of feed intake, coupled with a measure of animal liveweight (or mature weight) could potentially be used as an alternative measure of feed efficiency.