Shorten Paul R, Edwards Sara J, Juengel Jenny L
AgResearch Limited, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand.
AgResearch Limited, Invermay Research Centre, Puddle Alley, Private Bag 50034, Mosgiel, New Zealand.
Transl Anim Sci. 2021 Jan 28;5(1):txab013. doi: 10.1093/tas/txab013. eCollection 2021 Jan.
The reproductive performance of a sheep flock is dependent on a multitude of complex interacting factors. Attaining optimal flock performance requires information about how the reproductive steps are linked and relate to readily available measurements of the state of the flock. The goal was to use data from nine commercial flocks (greater than 300,000 records) to investigate and model the key reproductive steps affecting flock reproductive performance. We also developed a maximum-likelihood based methodology to predict flock ovulation rate based on measurements of the number of fetuses at mid-pregnancy (detected by ultrasound-scanning). The model was used to determine how changes in premating liveweight, age, predicted ovulation rate, number of fetuses at mid-pregnancy, lamb survival and lamb growth rate affect the total lamb liveweight at weaning per ewe exposed to the ram in each flock. The data from the commercial flocks were also used to investigate the role of ewe age and premating liveweight on each reproductive step. Sensitivity analyses were conducted to identify the key reproductive steps affecting flock reproductive performance, with a focus on understanding how these steps vary between flocks. The elasticity for embryo survival was 60% of that for lamb survival for these flocks and the elasticities for ovulation rate were highly variable between flocks (0.16 to 0.50 for mature ewes). This indicates that ovulation rate was near-optimal for some flocks, whereas there was potential to significantly improve flock performance in suboptimal flocks. The elasticity for ewe premating liveweight was highly variable between flocks (-0.03 to 0.84 for mature ewes and -0.18 to 1.39 for ewe lambs), indicating that premating liveweight ranged from optimal to suboptimal between flocks. For these suboptimal farms, the opportunity exists to increase flock performance through improved management of ewe premating liveweight. Reproductive loss was significantly greater in ewe lambs than mature ewes, although the difference is dependent on the stage of reproduction and flock. Predicted ovulation rate was 25% lower for ewe lambs and there was a 30% relative decrease in the predicted embryo survival probability from ovulation to scanning for ewe lambs. There was a 10% relative decrease in lamb survival probability from birth to weaning for ewe lambs and lamb growth rate was 25% lower for ewe lambs.
羊群的繁殖性能取决于众多复杂的相互作用因素。要实现最佳的羊群性能，需要了解繁殖步骤是如何关联的，以及它们与易于获得的羊群状态测量指标之间的关系。目标是利用来自9个商业羊群（超过30万条记录）的数据，来研究和建立影响羊群繁殖性能的关键繁殖步骤的模型。我们还开发了一种基于最大似然法的方法，根据怀孕中期胎儿数量（通过超声扫描检测）来预测羊群的排卵率。该模型用于确定配种前体重、年龄、预测排卵率、怀孕中期胎儿数量、羔羊存活率和羔羊生长率的变化如何影响每个羊群中每只与公羊接触的母羊断奶时的羔羊总活重。商业羊群的数据还用于研究母羊年龄和配种前体重在每个繁殖步骤中的作用。进行了敏感性分析，以确定影响羊群繁殖性能的关键繁殖步骤，重点是了解这些步骤在不同羊群之间是如何变化的。这些羊群中胚胎存活率的弹性是羔羊存活率弹性的60%，排卵率的弹性在不同羊群之间变化很大（成年母羊为0.16至0.50）。这表明，对于一些羊群来说，排卵率接近最佳水平，而在次优羊群中，有显著提高羊群性能的潜力。母羊配种前体重的弹性在不同羊群之间变化很大（成年母羊为-0.03至0.84，母羊羔羊为-0.18至1.39），这表明配种前体重在不同羊群之间从最佳到次优不等。对于这些次优农场，有机会通过改善母羊配种前体重的管理来提高羊群性能。母羊羔羊的繁殖损失明显大于成年母羊，尽管差异取决于繁殖阶段和羊群。母羊羔羊的预测排卵率低25%，从排卵到扫描时，母羊羔羊的预测胚胎存活概率相对下降30%。母羊羔羊从出生到断奶的羔羊存活概率相对下降10%，母羊羔羊的羔羊生长率低25%。
