Abstract At least 25% of lambs born in Australia die before marking. Research across southern Australia has demonstrated that reducing mob size at lambing by 100 ewes will, on average, increase the survival of single-born lambs by 0.8% and twin-born lambs by 2.2%. In this paper we assessed the economic value of lambing ewes in smaller mobs to improve lamb survival. The analysis considered scenarios for Merino and non-Merino flocks where producers subdivided lambing paddocks using temporary or permanent fencing, or where ewes were reallocated within existing paddocks based on ewe pregnancy status. Optimum mob sizes were most sensitive to the type of fencing used for subdivision, whether ewes were single- or twin-bearing, whether the effect of paddock size on potential stocking rate was included and the target return on investment. Breed, ewe stocking rate, scanning percentage and lamb price also impacted optimum mob size but had a smaller effect. The optimum mob size for twin-bearing Merino and non-Merino ewes was between 34% and 60% that of single-bearing ewes and this was similar for scenarios where paddocks were subdivided or ewes were reallocated within existing paddocks. Permanent subdivision of paddocks also presents an opportunity to increase stocking rate by capitalising on the benefits of improved pasture utilisation in smaller paddocks. The relationship between paddock size and pasture utilisation is not well quantified but it has an important effect on optimum mob and paddock size. The value of reallocating ewes within existing paddocks was greatest at a scanning percentage of 150% as this presents the greatest opportunity to alter mob sizes for single- and twin-bearing ewes. The economic return from adjusting the relative mob size of twin-bearing ewes from 100% to 50% that of single-bearing ewes was up to $0.27/Merino ewe/yr and $0.44/non-Merino ewe/yr with lamb at $6/kg carcass weight. Overall, these analyses demonstrate that reducing mob size at lambing can be a profitable strategy for improving lamb survival depending on the current size of lambing mobs. However, it is difficult to provide generic recommendations to producers for the optimum mob size of ewes and value of paddock subdivision because these are dependent on enterprise-specific factors.

中文翻译：

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影响产羔时母羊最佳群体大小的因素以及在较小群体中产羔以提高澳大利亚南部羔羊存活率的经济效益

摘要 在澳大利亚出生的羔羊中，至少有 25% 在标记前死亡。澳大利亚南部的研究表明，在产羔时减少 100 头母羊的群体规模平均会使单胎羔羊的存活率提高 0.8%，双胎羔羊的存活率提高 2.2%。在本文中，我们评估了在较小的群体中产羔的经济价值，以提高羔羊的存活率。该分析考虑了美利奴羊和非美利奴羊群的情景，即生产者使用临时或永久围栏细分产羔围场，或者根据母羊怀孕状况将母羊重新分配到现有围场内。最佳群体大小对用于细分的围栏类型最敏感，母羊是单胎还是双胎，是否包括围场大小对潜在放养率的影响以及目标投资回报。品种，母羊放养率、扫描百分比和羔羊价格也影响最佳群体规模，但影响较小。双胎美利奴和非美利奴母羊的最佳群体规模是单胎母羊的 34% 到 60%，这与细分围场或在现有围场内重新分配母羊的情况相似。围场的永久细分也提供了一个机会，通过利用在较小的围场中提高牧场利用率的好处来提高放养率。围场大小与牧场利用之间的关系尚未得到很好的量化，但它对最佳群体和围场大小有重要影响。在现有围场内重新分配母羊的价值最大，扫描百分比为 150%，因为这为改变单胎和双胎母羊的群体大小提供了最大的机会。将双胎母羊的相对群体规模从单胎母羊的 100% 调整为 50% 的经济回报高达 0.27 美元/美利奴母羊/年和 0.44 美元/非美利奴母羊/年，羊肉为 6 美元/公斤胴体重。总体而言，这些分析表明，在产羔时减少群体规模可能是提高羔羊存活率的有利策略，具体取决于产羔群体的当前规模。然而，很难向生产者提供关于母羊的最佳群体规模和围场细分价值的通用建议，因为这些取决于企业特定的因素。将双胎母羊的相对群体规模从单胎母羊的 100% 调整为 50% 的经济回报高达 0.27 美元/美利奴母羊/年和 0.44 美元/非美利奴母羊/年，羊肉为 6 美元/公斤胴体重。总的来说，这些分析表明，在产羔时减少群体规模可能是提高羔羊存活率的有利策略，具体取决于产羔群体的当前规模。然而，很难向生产者提供关于母羊的最佳群体规模和围场细分价值的通用建议，因为这些取决于企业特定的因素。将双胎母羊的相对群体规模从单胎母羊的 100% 调整为 50% 的经济回报高达 0.27 美元/美利奴母羊/年和 0.44 美元/非美利奴母羊/年，羊肉为 6 美元/公斤胴体重。总体而言，这些分析表明，在产羔时减少群体规模可能是提高羔羊存活率的有利策略，具体取决于产羔群体的当前规模。然而，很难向生产者提供关于母羊的最佳群体规模和围场细分价值的通用建议，因为这些取决于企业特定的因素。这些分析表明，在产羔时减少群体规模可能是提高羔羊存活率的有利策略，具体取决于产羔群体的当前规模。然而，很难向生产者提供关于母羊的最佳群体规模和围场细分价值的通用建议，因为这些取决于企业特定的因素。这些分析表明，在产羔时减少群体规模可能是提高羔羊存活率的有利策略，具体取决于产羔群体的当前规模。然而，很难向生产者提供关于母羊的最佳群体规模和围场细分价值的通用建议，因为这些取决于企业特定的因素。