Berry D P, Murphy T B
Teagasc, Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, P61 P302, Ireland.
School of Mathematics and Statistics, University College Dublin, Dublin, D04 V1W8, Ireland.
JDS Commun. 2025 May 1;6(3):345-349. doi: 10.3168/jdsc.2024-0705. eCollection 2025 May.
The ability to genomically predict the genetic merit of individuals coupled with the widespread availability of sex-sorted semen is causing a paradigm shift in global animal breeding. Many dairy producers wish to minimize the number of surplus dairy-bred calves born and, in turn, maximize the proportion of beef-on-dairy matings. The aim could be to select the number of candidate dams to be just sufficient to generate ample dairy-bred replacement progeny; using this strategy, minimal scope exists for selection within the resulting progeny cohort. However, the strategy of applying most of the selection pressure on the dam (and sire) ignores the contribution of the random segregation of genetic material during gametogenesis. The hypothesis of this study was that too strict selection within the candidate dam population for mating to dairy-sire semen with minimal opportunity for female progeny selection would affect genetic gain relative to generating surplus female progeny from which selection could then be exercised. Deterministic approaches were developed, complemented with simulations, where different intensity of selection in the dam and female progeny cohorts were imposed. Relative to the selection of the top ranking 10%, 20%, 30%, 40%, and 50% of candidate dams based on their genomic evaluation with 60% reliability, no preselection of dams coupled with genomically selecting the top ranking 10% to 50% of the female progeny born (also reliability of 60%) resulted in female progeny that were expected to, on average, have a true breeding value 0.58, 0.46, 0.38, 0.32, and 0.26 genetic SD higher. Benefits also existed from combining genomic selection within the cohort of candidate dams followed by genomic selection within the resulting female progeny. In most cases, herds will seek to generate ∼30% of their herd size as replacement heifers; based on the population parameters used, in such a scenario there is a clear benefit from selecting the top 60% of the candidate dams with the further gains thereafter being relatively small. This study provides the necessary equations to help producers make herd breeding decisions; the actual relative difference among different scenarios depends on the used population parameters.
基因组预测个体遗传价值的能力，再加上性别分选精液的广泛可得性，正在引发全球动物育种的范式转变。许多奶牛养殖户希望尽量减少出生的多余奶牛品种犊牛数量，进而最大化奶牛与肉牛杂交配种的比例。目标可能是选择数量刚好足以产生充足的奶牛品种替代后代的候选母畜；采用这种策略，在产生的后代群体中进行选择的空间很小。然而，将大部分选择压力施加于母畜（和公畜）的策略忽略了配子发生过程中遗传物质随机分离的作用。本研究的假设是，在候选母畜群体中进行过于严格的选择，以便与奶牛品种公畜精液配种，同时为雌性后代选择提供最小机会，相对于产生多余雌性后代然后从中进行选择而言，这会影响遗传进展。我们开发了确定性方法，并辅以模拟，在其中对母畜和雌性后代群体施加不同的选择强度。相对于基于60%可靠性的基因组评估选择排名前10%、20%、30%、40%和50%的候选母畜，不进行母畜预选，而是对出生的雌性后代进行基因组选择，选择排名前10%至50%（可靠性同样为60%），结果产生的雌性后代平均预期真实育种值分别高出0.58、0.46、0.38、0.32和0.26个遗传标准差。在候选母畜群体中进行基因组选择，随后在产生的雌性后代中进行基因组选择，也存在益处。在大多数情况下，牛群会寻求培育约30%的牛群规模作为后备小母牛；基于所使用的群体参数，在这种情况下，选择排名前60%的候选母畜有明显益处，此后进一步的收益相对较小。本研究提供了必要的公式，以帮助养殖户做出牛群育种决策；不同方案之间的实际相对差异取决于所使用的群体参数。
