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The reproductive performance of Merino ewe lambs is highly variable and generally poor in comparison to older ewes. In this study, we determined the impacts of growth pattern to the end of the mating period and sire genetics on the reproductive performance of Merino ewe lambs. Five hundred ewe lambs with full pedigree records were managed under commercial conditions from weaning and weighed 43.5 kg at the start of the mating period with an average age of 224 days. The ewe lambs were offered a moderate or high feed allowance to achieve target growth rates of 100 or 200 g/day during a 46-day mating period. They were then recombined and scanned for pregnancy status 60 days after the mating period. At the individual animal level, a 5 kg greater live weight at the start of the mating period increased reproductive rate (foetuses per 100 ewes joined) by about 20% (P

Improving the survival of twin-born lambs is a high priority for the Australian sheep industry. Higher mob sizes at lambing have been suggested to decrease the survival of twin-born lambs. However, our recent work indicated that this effect may not occur when feed-on-offer (FOO) exceeds 2400 kg DM/ha during the lambing period. Increasing mob size at lambing when FOO is limited may exacerbate the risk of mismothering due to the need for ewes to seek feed and thus result in poorer lamb survival. Therefore, this study tested the hypothesis that (i) a higher mob size at lambing will decrease lamb survival when FOO from pasture is limited and ewes are supplementary fed and (ii) that this is related to a greater rate of interaction with foreign ewes and lambs during the periparturient period. Twin-bearing Merino ewes (n = 795) were allocated into one of two treatments on day 140 of pregnancy; high (n = 210) or low (n = 55) mob size, with three replicates of each treatment. Feed-on-offer from live pasture at lambing was below 390 kg DM/ha and ewes were supplementary fed until lamb marking. Behaviour during the periparturient period was observed and dead lambs were collected for autopsy for 14 days during the peak of lambing. The survival of lambs to marking was recorded for each mob. Lamb survival was 6.2% higher at the low compared to the high mob size (P

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.