Oloo R D, Mrode R, Ekine-Dzivenu C C, Ojango J M K, Bennewitz J, Gebreyohanes G, Okeyo A M, Chagunda M G G
Animal Breeding and Husbandry in the Tropics and Subtropics, University of Hohenheim, Stuttgart, Germany.
Livestock Genetics, International Livestock Research Institute, Nairobi, Kenya.
J Anim Breed Genet. 2025 Nov;142(6):630-642. doi: 10.1111/jbg.12933. Epub 2025 Mar 3.
Change in climate over the past years and its impact on the environment have necessitated the inclusion of resilience traits in the breeding objectives of dairy cattle. However, the relationship between resilience and other traits of economic importance in dairy production is currently not well known. This study examined the genetic parameters and relationships among resilience, fertility and milk production traits in dairy cattle in Kenya. Indicators of general resilience and heat tolerance were defined from the first parity test-day milk yield records. Indicators of general resilience included variance of actual deviations (LnVar1), variance of standardised deviations (LnVar2), lag-1 autocorrelation (r) and skewness (Skew) of standardised deviations in milk yield. Heat tolerance indicators at temperature-humidity index 80 included the slope of the reaction norm (Slope), absolute slope of the reaction norm (Absolute), and the intercept of the reaction norm model (Intercept). Cows with > 50% taurine genes had lower age at first calving (AFC), longer calving intervals (CI) and higher test-day milk yield (MY). The heritability estimates of AFC, CI and MY were 0.17 ± 0.033, 0.06 ± 0.012 and 0.35 ± 0.021, respectively. The repeatability estimates of CI and MY were 0.06 ± 0.012 and 0.47 ± 0.009, respectively. The low heritability and non-significant permanent environmental variance of CI showed that CI is heavily influenced by external factors, such as management practices. AFC was negatively genetically correlated with both CI (-0.88 ± 0.077) and MY (-0.53 ± 0.059) showing that animals that attain sexual maturity earlier exhibit longer CI and higher milk production. A positive genetic correlation (0.62 ± 0.077) between CI and MY shows that high-yielding cows face challenges in maintaining shorter calving intervals. Heritability estimates of nearly all resilience indicators were significant and ranged from 0.05 to 0.34. Heat tolerance indicators showed low to non-significant genetic correlations with general resilience indicators, suggesting that different genetic factors are involved in responses to different types of disturbances. There was a generally positive genetic correlation between resilience and fertility, implying that resilient animals might have better fertility. All indicators, except LnVar1 and LnVar2, revealed an antagonistic genetic relationship between resilience and milk production. The findings present an opportunity for including resilience in the development and application of selection indices in dairy cattle, especially for the tropics.
过去几年气候变化及其对环境的影响，使得在奶牛育种目标中纳入抗逆性性状成为必要。然而，目前尚不清楚抗逆性与奶牛生产中其他重要经济性状之间的关系。本研究调查了肯尼亚奶牛抗逆性、繁殖力和产奶性状之间的遗传参数及关系。根据头胎测定日产奶量记录定义了一般抗逆性和耐热性指标。一般抗逆性指标包括实际偏差的方差（LnVar1）、标准化偏差的方差（LnVar2）、滞后1自相关（r）以及日产奶量标准化偏差的偏度（Skew）。温度 - 湿度指数为80时的耐热性指标包括反应规范的斜率（Slope）、反应规范的绝对斜率（Absolute）以及反应规范模型的截距（Intercept）。具有> 50% 牛磺酸基因的奶牛初产年龄（AFC）较低，产犊间隔（CI）较长，测定日产奶量（MY）较高。AFC、CI和MY的遗传力估计值分别为0.17±0.033、0.06±0.012和0.35±0.021。CI和MY的重复性估计值分别为0.06±0.012和0.47±0.009。CI的低遗传力和不显著的永久环境方差表明，CI受管理实践等外部因素的严重影响。AFC与CI（-0.88±0.077）和MY（-0.53±0.059）均呈负遗传相关，表明性成熟较早的动物产犊间隔较长且产奶量较高。CI与MY之间存在正遗传相关（0.62±0.077），表明高产奶牛在维持较短产犊间隔方面面临挑战。几乎所有抗逆性指标的遗传力估计值均显著，范围为0.05至0.34。耐热性指标与一般抗逆性指标的遗传相关性较低至不显著，表明对不同类型干扰的反应涉及不同的遗传因素。抗逆性与繁殖力之间总体上存在正遗传相关，这意味着抗逆性强的动物可能具有更好的繁殖力。除LnVar1和LnVar2外，所有指标均显示抗逆性与产奶量之间存在拮抗遗传关系。这些发现为在奶牛选择指数的制定和应用中纳入抗逆性提供了机会，特别是在热带地区。
