Bronwyn Clarke

This study evaluated the impacts of management of body condition score (BCS) between pregnancy scanning and lamb marking on the mortality of triplet-bearing ewes and their lambs at 19 research sites across Southern Australia. Triplet-bearing ewes of Maternal (crossbred or composite) or Merino breed were randomly allocated to treatment at pregnancy scanning at an average of 97 days from the start of joining: High or Low BCS. The BCS of individual ewes was assessed at pregnancy scanning, pre-lambing (average of 137 days from the start of joining) and marking (average of 165 days from the end of joining), and ewe and lamb mortality to marking, recorded for each mob. The average BCS at pregnancy scanning was 3.4 for Maternal ewes and 3.3 for Merino ewes. There were no breed by BCS treatment effects on the BCS of ewes at pregnancy scanning or lamb marking or on the change in BCS between pregnancy scanning and pre-lambing or between pre-lambing and marking. The change in BCS differed between the High and Low BCS treatments, between pregnancy scanning and pre-lambing (0.12 vs. −0.33; p < 0.001) and between pre-lambing and marking (−0.39 vs. 0.07; p < 0.001) but did not differ between breeds. The average BCS at marking for ewes managed at the High and Low BCS treatments was 3.1 and 3.0 for Maternals and 3.0 and 2.8 for Merinos. Survival of triplet-bearing Merino ewes (p < 0.01) and their lambs (p < 0.001) was greater when ewes were managed at the High BCS compared to the Low BCS. The BCS treatment did not impact the survival of Maternal ewes or their lambs. The survival of Merino but not Maternal lambs was higher when ewes were in greater BCS pre-lambing (p < 0.01) and when ewes gained BCS between pregnancy scanning and pre-lambing (p < 0.01). Ewe mortality was lower when ewes gained BCS between pregnancy scanning and pre-lambing (p < 0.05). Merino ewes were more likely to die than Maternal ewes for a given change in BCS between pregnancy scanning and pre-lambing (p = 0.065). Overall, our findings demonstrate that producers should manage the nutrition of triplet-bearing Merino ewes so that ewes are in greater BCS at lambing and/or to gain BCS between pregnancy scanning and lambing to improve ewe and lamb survival. Triplet-bearing Maternal ewes should be managed to gain BCS between pregnancy scanning and lambing to improve ewe survival.

Feed intake, methane and feed efficiency have important genetic correlations with growth, carcase weights and mature size that need to be considered when breeding for production whilst reducing feed requirements and methane production in the Australian sheep industry. Live weight, growth, fat and muscle have significant antagonistic relationships with feed intake, which may make simultaneous selection for efficiency traits and, growth and meat quality slower. For example, selecting animals that grow faster is known to reduce meat eating quality. Therefore, we estimated the genetic and phenotypic correlations between feed intake, residual feed intake, methane, carbon dioxide, oxygen, live-weight, growth, fat and muscle depth traits. Fat and muscle depth were corrected for live weight. Traits were recorded on Merino sheep (n=2717) in Western Australia between 2010 and 2016. Sheep were measured at post-weaning (range 753 to 2717 records across traits), hogget (∼18 months old; range 602 to 1046) and adult ages (>2 years old; range 269 to 443). Live-weight and growth rate had significant moderate to high positive genetic correlations with feed intake, residual feed intake, methane and carbon dioxide at post-weaning, hogget and adult ages. Fat and muscle depth measured at the start and finish of the feed intake measurement period generally had negative genetic correlations with residual feed intake, feed intake and methane. These genetic correlations with feed intake and residual feed intake were more negative with fat and muscle measured at the start of the measurement period than at the end. Furthermore, in young sheep, selecting for lower feed intake and residual feed intake will mean lower change in fat between the start and finish of the intake period. Fat and muscle had significant correlations with feed efficiency and greenhouse gas traits and should therefore be considered when estimating residual feed intake, particularly in young animals.

Industry consultation in Australia revealed that the potential impact of the mob size of ewes during lambing on the survival of triplet-born lambs was an important research priority. Previous research has demonstrated that smaller mob sizes at lambing improve the survival of single- and especially twin-born lambs, regardless of ewe stocking rate. Therefore, we hypothesised that lambing triplet-bearing ewes in smaller mobs, regardless of stocking rate, will increase the survival of their lambs. Research sites were established on 12 commercial sheep farms across southern Australia between 2019 and 2021. One farm used Merinos whilst the remainder of the farms used non-Merino breeds, consisting of composite ewes joined to composite or terminal sires. Three of the farms were used in two years of the experiment. Adult, triplet-bearing ewes were randomly allocated into one of two treatments, ‘High’ or ‘Low’ mob size, at an average of 135 days from the start of joining. Ewe and lamb survival were assessed between allocation to treatments and lamb marking. Lamb survival was significantly greater for lambs born in the Low (65.6%) compared with the High (56.6%) mob size treatments (p < 0.001). There was no effect of mob size at lambing on the mortality of triplet-bearing ewes. Analysis of the effect of the actual mob sizes showed that reducing the mob size at lambing by 10 triplet-bearing ewes increased the survival of their lambs to marking by 1.5% (p < 0.001). This study has shown that the survival of triplet-born lambs can be improved by lambing triplet-bearing ewes in smaller mobs regardless of stocking rate when ranging from 0.7–13 ewes/ha.

The eruption of the first permanent incisors in sheep determines the classification of lamb and hogget and impacts the sale value of animals in Australia. This study tested the hypothesis that the age of incisor eruption would differ between progeny from different Merino sires and would occur earlier for progeny that were heavier at 12 months of age. The study utilised wether progeny at a site in Western Australia from 29 sires born in 2016 (n = 347) or 2017 (n = 553), and ewe and wether (castrated male) progeny at a second site in New South Wales from 29 sires born in 2017 (n = 713 ewes and 343 wethers) or 2018 (n = 638 ewes and 457 wethers). Classing of incisor eruption commenced at 10–11 months of age and was recorded monthly until 19 or 20 months of age at the two sites. The average age of incisor eruption varied by up to 2.5 months between sire groups (P < 0.001) and incisor eruption was completed for all progeny within a sire group over three months for some sires but over 6 months for other sires. Incisor eruption occurred earlier for animals that were heavier at 12 months of age (P < 0.001). The period when animals gained weight up to 12 months also influenced incisor eruption, as differences in liveweight at weaning had twice the effect on age of incisor eruption compared with differences in liveweight gain post-weaning at both sites. Estimated stage of maturity at 12 months of age had minimal effects on subsequent age of incisor eruption, and regardless, the large variation in age of incisor eruption between sires were not accounted for by liveweight or stage of maturity at 12 months. In addition to selecting Merino sires that produce progeny that can be sold as lamb at an older age, farmers may also benefit from understanding the pattern of the first permanent incisors eruption specific to their genotype and monitoring liveweights and liveweight change to optimise the time and value of animals at sale.

Suboptimal reproductive performance of maiden (primiparous) ewes remains a source of inefficiency for the Australian sheep industry. However, the extent and causes of the poorer reproductive performance of maiden ewes on Australian sheep farms are not well understood. Here, we show the reproductive performance of maiden ewes relative to their multiparous counterparts on the same farms across Australia using a cohort survey. The difference in marking rate for non-Merino maiden ewe lambs compared to multiparous ewes was 58% (74 vs. 132%; p < 0.001), and this was attributable to a 50% difference in reproductive rate (109 vs. 159%; p < 0.001) and 16% difference in lamb survival to marking (67 vs. 83%; p < 0.001). The difference in marking rate for maiden Merino two-tooth ewes lambing at approximately 2 years-of-age compared to mature multiparous ewes was 22% (80 vs. 102%; p < 0.001) and this was attributable to a 24% difference in reproductive rate (108 vs. 132%; p < 0.001) and 3% difference for lamb survival (75 vs. 78%; p < 0.05). Positive correlations for reproduction traits (reproductive rate, lamb survival and marking rate) between maidens and multiparous ewes were observed for maiden Merino two-tooth ewes (p < 0.001), but these correlations were weak or non-existent for non-Merino ewe lambs. Strategies to improve both reproductive rate and lamb survival can address the poorer and more variable reproductive performance of maiden ewes.