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Context Increasing mating weight or condition score increases the lambing potential of ewes (fetuses scanned per 100 ewes joined). Aim We hypothesised that in some years, condition score would contribute an additional effect to mating weight on lambing potential. Methods Border Leicester Merino and Merino ewes were mated naturally to Merino or Terminal rams between 2008 and 2013 at eight linked sites across Australia. Border Leicester Merino ewes were mated in their first year while Merino ewes were not mated until their second year. All ewes were mated for a second time as 2 year olds (Border Leicester Merinos) or 3 year olds (Merino). A total of 4270 Border Leicester Merino and 5788 Merino ewes were weighed and condition scored at mating and scanned for pregnancy. Key results Lambing potential increased by 3.1% per 1 kg increase in mating weight, compared to 1.3% for 1 and 2 year old Border Leicester Merinos respectively, and by 2.1% compared to 1.4% for 2 and 3 year old Merinos respectively (P

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

Limited research has suggested that higher lambing densities increase interference from foreign ewes at lambing which disrupts the ewe-lamb bond and compromises lamb survival. This may be particularly evident in mobs of twin-bearing ewes compared to single-bearing ewes because a greater number of lambs are born per day. Therefore, we hypothesised that; (i) decreasing the mob size of ewes at lambing has a greater impact on the survival of twin-born lambs than single-born lambs; (ii) the relationship between mob size and lamb survival can be explained by differences in the rate of interaction with foreign ewes and lambs at lambing; and (iii) ewes will utilise a limited area of the paddock at lambing and thus lambing density will be defined by the distribution of ewes in the paddock rather than the paddock area. Merino ewes were allocated into a 2×2 factorial combination of ewe pregnancy status (single- or twin-bearing) and mob size (high (n=130 ewes) or low (n=50 ewes)) on day 140 from the start of joining. Each treatment had two replicates excepting the low mob size for twins which had a third replicate. Ewes lambed at a stocking rate of 11 ewes/ha. Feed-on-offer during lambing exceeded 2400 kg dry matter (DM)/ha. Ewe-lamb behaviour was observed and dead lambs were autopsied over 11 days during the peak of lambing. The distribution of ewes in each paddock was recorded every 2 h during daylight hours by counting the number of ewes occupying 2500 m2 grids. The proportion of ewes and their newborn progeny which interacted with foreign ewes at lambing did not differ between the high and low mob sizes for single- (24.9% v. 20.8%) or twin-bearing ewes (14.3% v. 19.6%; P=0.74). Similarly, interaction with foreign lambs did not differ between the high and low mob sizes for single- (14.5% v. 25.2%) and twin-bearing ewes (34.5% v. 26.4%; P=0.44). The distribution of ewes within the paddock did not differ between treatments (P=0.95). On average, single-bearing ewes which lambed at the high and low mob sizes occupied 34% and 36% of the paddock during daylight hours, and the corresponding values for twin-bearing ewes were 40% and 43%. Survival of twin-born lambs was lower than single-born lambs (75.3% v. 87.9%; Plt;0.01), however, lamb survival was not influenced by mob size regardless of birth type. These results suggest that higher mob sizes may not compromise lamb survival when feed-on-offer during lambing exceeds 2400 kg DM/ha.

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.

Knowing the birth date of lambs is important for the accuracy of breeding values, particularly when ranking potential sires for liveweight and growth. We used proximity sensors to measure the daily interactions between ewes and rams to test the hypothesis that the birth date of lambs could be predicted from the time of highest interactions between ewes and rams during joining. This was a pilot project with two plots of ewes (29 or 42 ewes per plot) and one ram per plot for a 26 day joining period. The day in which the ewe had the highest ratio of interactions with the ram relative to the other ewes in the plot was selected typically as the estimated day of conception. A threshold ratio of 1.5 was used which eliminated six ewes (the number of interactions between the ewe and ram compared with the average number of daily interactions for all ewes with the ram in the plot). The prediction of the date of birth was within five days of the actual birth date for 100% of the ewes (n = 55) and within two days for 82% of the ewes. Eighty five percent of the variation in date of birth of lambs was explained by the estimated date of conception. Using the remote sensors was a discreet way of measuring mating behaviour that proved to be a good tool for predicting the birth date of lambs. This can help breeders improve the accuracy of breeding values and the ranking of sires for early growth traits.