Research and Development, Livestock Improvement Corporation, Hamilton, New Zealand 3286.
Emerging Markets and Innovation, Livestock Improvement Corporation, Hamilton, New Zealand 3286.
J Dairy Sci. 2018 May;101(5):4650-4659. doi: 10.3168/jds.2017-13538. Epub 2018 Feb 15.
The genetic merit of a herd is a key determinant in productivity for dairy farmers. However, making breeding decisions to maximize the rate of genetic gain can be complex because there is no certainty about which cows will become pregnant with a heifer calf. In this study, breeding worth (BrW) was used as a measure of genetic merit, and several mating strategies were evaluated. These strategies included randomly mating whole herds to the entire bull team, excluding low-ranked cows from producing replacement heifers, and nominating high-ranked cows to the most highly ranked bulls. Simulations were undertaken using 4 bull teams generated from bulls currently marketed in New Zealand and a selection of New Zealand dairy herds. Average replacement heifer BrW was calculated for 1,000 iterations of each combination of mating strategy, herd, and bull team (scenario). Variation in resulting average replacement heifer BrW within scenarios was due to random sampling of which cows became pregnant with a heifer calf. Relative to mating the whole herd to an entire bull team, excluding the lowest ranked cows from producing replacements resulted in the greatest increase in average replacement heifer BrW across all herds and bull teams, with a gain of approximately 0.4 BrW point for each 1% of cows excluded. Nominating top-ranking cows to the highest ranking bulls in the team had little effect (0.06-0.13 BrW increase for each 1% of top cows nominated) in improving BrW of replacement heifers. The number of top bulls nominated had a variable effect depending on the BrW spread of the entire bull team. Although excluding cows with the lowest BrW from producing replacement heifers is most effective for improving BrW, it is important to ensure that the number of heifers born is sufficient to replace cows leaving the herd. It is likely that optimal strategies for improving BrW will vary from farm to farm depending not only on the BrW structure of the herd, the bull team available, and the reproduction success on farm but also on farm management practices. This simulation study provides expected outcomes from a variety of mating strategies to allow informed decision making on farm.
牛群的遗传优势是奶农生产力的关键决定因素。然而，要做出最大限度提高遗传增益的繁殖决策可能很复杂，因为不能确定哪些奶牛会怀上小母牛。在这项研究中，繁殖价值（BrW）被用作遗传优势的衡量标准，并评估了几种交配策略。这些策略包括将整个牛群随机配种给整个公牛队，将低排名的奶牛排除在生产后备小母牛之外，以及提名高排名的奶牛给排名最高的公牛。使用从新西兰市场上现有的公牛生成的 4 个公牛队和一些新西兰奶牛场，对这些策略进行了模拟。对每种交配策略、牛群和公牛队（方案）的 1000 次迭代的平均后备小母牛 BrW 进行了计算。方案内的平均后备小母牛 BrW 的变化是由于随机抽样哪些奶牛怀上了小母牛。与将整个牛群配种给整个公牛队相比，将排名最低的奶牛排除在生产后备牛之外，可以使所有牛群和公牛队的平均后备小母牛 BrW 最大程度地增加，每排除 1%的奶牛，BrW 就会增加约 0.4 个点。将排名最高的奶牛提名给团队中排名最高的公牛，对提高后备小母牛的 BrW 影响很小（提名每 1%的顶级奶牛，BrW 增加 0.06-0.13 个点）。提名的顶级公牛数量的影响取决于整个公牛队的 BrW 分布。虽然将 BrW 最低的奶牛排除在生产后备牛之外对于提高 BrW 最有效，但确保出生的小母牛数量足以替代离开牛群的奶牛非常重要。提高 BrW 的最佳策略可能因农场而异，这不仅取决于牛群的 BrW 结构、可用的公牛队以及农场的繁殖成功率，还取决于农场管理实践。本模拟研究提供了各种交配策略的预期结果，以便在农场做出明智的决策。
