Amy Lockwood

Context: Lambing triplet-bearing ewes in smaller mobs significantly increases lamb survival. Aims: This paper reports economic analysis to assess the optimum mob size for triplet-bearing ewes during lambing. Methods: The analyses considered scenarios for Merino and non-Merino (Maternal) flocks where producers subdivided lambing paddocks using permanent fencing or where ewes were re-allocated within existing paddocks on the basis of pregnancy status. Key results: The optimum mob sizes for triplet-bearing ewes during lambing were affected by ewe breed, stocking rate, lamb price and the target return-on-investment if subdividing paddocks. The optimum mob size for triplet-bearing Maternal and Merino ewes was between 27% and 40% of the optimum for twin-bearing ewes and this was similar for scenarios where paddocks were subdivided, or where ewes were re-allocated within existing paddocks. At the standard lamb price of AUD$7/kg carcass weight, the economic return from adjusting the relative mob size of triplet-bearing ewes was AUD$2.05 per multiple-bearing or AUD$14.20 per triplet-bearing Maternal ewe and AUD$0.54 per multiple-bearing ewe or AUD$5.70 per triplet-bearing Merino ewe. Conclusions: Overall, these analyses demonstrated that reducing mob size at lambing can be a profitable strategy for improving survival of triplet-born lambs, depending on the current size of lambing mobs. Implications: As reported previously for single- and twin-bearing ewes, it is difficult to provide generic recommendations to producers for the optimum mob size of triplet-bearing ewes at lambing because optimum mob size was dependent on several enterprise-specific factors.

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.

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.

Consultation with sheep producers was used to quantify the mortality of triplet-bearing ewes and their lambs, identify management practices adopted by producers to reduce these losses and prioritise future research needs to improve the survival of triplet-bearing ewes and their lambs. Surveys were completed by 64 producers across Australia who identified and separated triplet-bearing ewes from twin-bearing ewes in 2017 and/or 2018. On average, 5.9% of all ewes mated were identified as carrying triplets (6.6% of non-Merino ewes and 2.9% of Merino ewes). The average mortality of triplet-bearing ewes was 6.4%, and ewe mortality did not differ significantly between ewe breeds. The average survival of triplet-born lambs was 59%, and survival was significantly higher for lambs from non-Merino compared to Merino ewes (60.1 vs. 52.9%, p < 0.05). The key strategies adopted to reduce the mortality of triplet-bearing ewes and their lambs included management of condition score, feed-on-offer, mob size at lambing and use of shelter. There were no differences (p > 0.05) in the average mortality of triplet-bearing ewes or their lambs between producers that prioritised the adoption of certain management practices. However, significant variation existed between producers in their targets at lambing for ewe condition score (2.8 to 3.5), mob size (10 to 150 ewes) and feed-on-offer (800 to 2500 kg dry matter/ha). Overwhelmingly, the highest priorities for further research identified by producers from surveys, workshops and a webinar were ewe condition score, mob size, feed-on-offer at lambing and mineral supplementation. This study informs benchmarks for mortality of triplet-bearing ewes and their lambs under extensive grazing conditions in Australia, and the priorities for future research to reduce these losses.

Shade and shelter may provide protection from cold and heat stress, a source of feed during prolonged or seasonal drought, specific essential nutrients, increased pasture and crop production and improved landscape health. Cold stress contributes to the average of 8% (single) and 24% (twin) of lambs that die within 3 days of birth in Australia and the estimated 0.7% of the Australian flock that die post-shearing during extreme or unseasonal weather. Shelter has resulted in an average reduction in mortality of 17.5% for twin-born lambs and 7% for single-born lambs according to Australian studies and decreases the susceptibility of ewes to metabolic disease and possibly dystocia. Because many of the published studies are from research areas where cold stress is expected, they are not indicative of industry-wide responses, a research priority is to determine the probability of lamb and ewe deaths from cold stress across different sheep production areas. Although shelter may improve lamb survival, ewes do not always choose to lamb in a sheltered location. For this reason, there is a requirement for research into the voluntary use of shelter in commercial-sized paddocks and the role that nutritive value of shelter plays in attracting and holding ewes to shelter, and to their lambs. Heat stress may also result in lamb deaths and influences feed conversion efficiency, appetite, reproduction, wool growth and disease susceptibility. The consequences of heat stress may go unnoticed over a yearly production cycle, although there is some evidence that shade may increase weaning rates and feed intake of grazing sheep. There are ancillary benefits from shade and shelter. Trees may improve crop production through reducing wind damage and evapotranspiration and provide timber. Shrubs provide feed during the summer–autumn feed gap or drought, are useful for the management of land degradation and provide habitat for native fauna. It is clear that shade and shelter in the correct locations provide a range of benefits to livestock and the landscape; nevertheless, adoption appears low. Research that focuses on defining the benefits on a farm or landscape scale is required to support extension programs.

The contribution of abortions to the overall mortality of lambs born to maiden (primiparous) ewes in Australia remains unclear. This cohort study aimed to quantify abortion and lamb mortality for ewe lambs and maiden Merino two-tooth ewes. Lamb mortality from pregnancy scanning to marking were determined for 19 ewe lamb and 11 Merino two-tooth ewe flocks across southern Australia. Average lamb mortality from scanning to marking was 35.8% (range 14.3–71.1%) for the ewe lambs and 29.4% (range 19.7–52.7%) for the two-tooth ewes. Mid-pregnancy abortion was detected in 5.7% of ewes (range 0–50%) in the ewe lamb flocks and 0.9% of ewes (range 0–4.4%) in the two-tooth ewe flocks. Mid-pregnancy abortion affecting ≥2% of ewes was observed in 6/19 ewe lamb flocks and 2/11 two-tooth ewe flocks. Lamb mortality from birth to marking represented the greatest contributor to foetal and lamb mortality after scanning, but mid-pregnancy abortion was an important contributor to lamb mortality in some ewe lamb flocks. Variability between the flocks indicates scope to improve the overall reproductive performance for maiden ewes by reducing foetal and lamb losses. Addressing mid-pregnancy abortion may improve the reproductive performance in some flocks.

Context: Data collected from producers in south-eastern Australia found that the survival of twin-born lambs decreased by 3.5% for each extra 100 ewes in the mob at lambing. Increasing stocking rate by 1 ewe/ha decreased lamb survival by a further 0.7%. These survey findings suggest that lamb survival could be improved by optimising the allocation of ewes to mobs and paddocks at lambing. Aim: The present paper reports two experiments. Experiment 1 tested the hypotheses that (1) the survival of twin-born lambs would be greater when ewes lamb in smaller mobs and at lower stocking rates, and (2) the effects of mob size and stocking rate would be greater in Merinos than in non-Merino breeds. Experiment 2 tested the hypothesis that the survival of twin-born Merino lambs would be greater at lower mob sizes when ewes lambed at stocking rates <4 ewes/ha. Methods: Experiment 1 investigated a 2 × 2 factorial combination of mob size (high or low) and stocking rate (high or low) on the survival of twin-born Merino and non-Merino lambs at 70 on-farm research sites across southern Australia. Experiment 2 investigated the effect of high or low mob size on the survival of twin-born Merino lambs when ewes lambed at stocking rates of <4 twin ewes/ha at 15 on-farm research sites. In both experiments, adult twin-bearing ewes were randomly allocated into a treatment and lambing paddock on Day 140 from the start of joining at each farm. Lamb survival in each mob was calculated based on lamb losses between pregnancy scanning and lamb marking. Key results: In both experiments, the effect of mob size on lamb survival was found to be linear, with survival of twin-born lambs decreasing by between 1.9% and 2.5% per additional 100 ewes in the mob at lambing, regardless of breed (P < 0.001). In Experiment 1, there was no effect of stocking rate or mob size by stocking rate on lamb survival. Conclusions: The present research demonstrated that reducing mob size but not stocking rate will improve the survival of twin-born lambs to marking for extensive enterprises in Australia where ewes lamb at stocking rates of up to 12 ewes/ha. Implications: These findings will contribute to guidelines for optimising ewe nutrition and resource allocation to improve lamb survival.

Higher stocking rates of lambing ewes have been associated with poorer ewe‐lamb behaviour and lamb survival. This study tested the hypothesis that increasing the mob size and stocking rate of lambing ewes on commercial farms will reduce the survival of their lambs. Data were collected from 66 producers in Australia for Experiment one and 22 producers in New Zealand for Experiment two. Survival of single‐ and twin‐born lambs decreased by 1.4% and 3.5% per extra 100 ewes in the mob, regardless of breed, in Experiment one. The survival of Merino lambs in Experiment two decreased by 0.9% per extra 100 ewes in the mob, regardless of birth type. Increasing stocking rate by 1 ewe/ha also decreased lamb survival by 0.7% in Experiment one. However, this was not evident in Experiment two. These findings highlight the scope to optimise ewe mob size and stocking rate at lambing to improve lamb survival.