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.

中文翻译：

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在产羔时减少母羊的群体规模而不是放养率增加了澳大利亚南部农场出生的双胞胎羔羊的存活率

背景 从澳大利亚东南部的生产商收集的数据发现，在产羔时，每多 100 只母羊，双胞胎羔羊的存活率就会降低 3.5%。将放养率提高 1 只母羊/公顷，羔羊存活率进一步降低 0.7%。这些调查结果表明，可以通过优化母羊在产羔时对暴徒和围场的分配来提高羔羊的存活率。目的本文报告了两个实验。实验 1 检验了以下假设：(1) 当母羊羔在较小的群体中和较低的放养率时，双胞胎羔羊的存活率会更高，以及 (2) 群体大小和放养率对美利奴羊的影响会大于美利奴羊非美利奴品种。实验 2 检验了以下假设：当母羊以低于 4 只母羊/公顷的产羔率产羔时，双胎美利奴羔羊的存活率在较低的群体规模下会更高。方法 实验 1 在澳大利亚南部 70 个农场研究地点调查了对双胞胎美利奴羊和非美利奴羊羔存活率的 2 × 2 因子组合（群体大小（高或低）和放养率（高或低）。实验 2 调查了在 15 个农场研究地点，当母羊以 <4 双胎母羊/公顷的放养率产羔时，高或低的群体大小对双胎美利奴羊羔存活率的影响。在这两个实验中，从每个农场开始加入的第 140 天，成年双胎母羊被随机分配到处理和产羔围场。根据妊娠扫描和羔羊标记之间的羔羊损失计算每个暴民中的羔羊存活率。主要结果 在这两个实验中，发现群体大小对羔羊存活率的影响呈线性，双胞胎羔羊的存活率下降了 1.9% 到 2%。产羔时每增加 100 头母羊 5%，无论品种如何（P < 0.001）。在实验 1 中，放养率或群体大小对羔羊存活率没有影响。结论 目前的研究表明，减少群体规模而不是放养率将提高双胞胎羔羊的存活率，以便在澳大利亚的粗放型企业中，母羊羔羊的放养率高达 12 只/公顷。意义 这些发现将有助于制定优化母羊营养和资源分配以提高羔羊存活率的指南。结论 目前的研究表明，减少群体规模而不是放养率将提高双胞胎羔羊的存活率，以便在澳大利亚的粗放型企业中，母羊羔羊的放养率高达 12 只/公顷。意义 这些发现将有助于制定优化母羊营养和资源分配以提高羔羊存活率的指南。结论 目前的研究表明，减少群体规模而不是放养率将提高双胞胎羔羊的存活率，以便在澳大利亚的粗放型企业中，母羊羔羊的放养率高达 12 只/公顷。意义 这些发现将有助于制定优化母羊营养和资源分配以提高羔羊存活率的指南。