Magro S, De Marchi M, Cassandro M, Finocchiaro R, Fabris A, Marusi M, Costa A
Department of Agronomy, Food, Natural resources, Animals and Environment, University of Padova, Legnaro, Italy 35020.
Department of Agronomy, Food, Natural resources, Animals and Environment, University of Padova, Legnaro, Italy 35020.
J Dairy Sci. 2025 Mar;108(3):2683-2696. doi: 10.3168/jds.2024-25170. Epub 2024 Dec 7.
At the onset of lactation, high-producing dairy cows commonly face a negative energy balance and metabolic disorders, such as hyperketonemia. Blood concentrations of nonesterified fatty acids (NEFA), BHB, cholesterol, glucose, and urea provide valuable information about the metabolic, health, and nutritional status of lactating cows. Milk mid-infrared (MIR) spectroscopy has been successfully used for the prediction of several health traits in the last years, including blood metabolite concentrations, even though the model accuracy is moderate. In fact, MIR-predicted blood parameters are useful for population screening and may be used for selective breeding if they are heritable and genetically variable within a population. In the present study, we estimated h and genetic correlations of BHB, NEFA, glucose, cholesterol, and urea and assessed their genetic correlations with milk yield and composition traits in the Italian Holstein population using phenotypes of 9,943 cows in 460 herds. Two datasets were considered: early lactation (8,277 test-day records between 5 and 35 DIM) and whole lactation (105,293 test-day records, between 5 and 305 DIM). The h and genetic variability of blood traits were greater in early than whole lactation, suggesting that there is room to manipulate metabolic disease incidence in the transition period through tailored genetic strategies. Blood BHB was the most heritable trait, regardless of the lactation stage (with h of 0.13 and 0.08 in early and whole lactation), whereas blood NEFA was the least heritable trait, with h not significantly different from zero. Blood BHB was positively genetically correlated with NEFA, whereas glucose was negatively correlated with BHB, NEFA, and urea. The milk fat-to-protein ratio was correlated with BHB, NEFA, and cholesterol, whereas a negative correlation was calculated between lactose content and BHB and between SCS and BHB. Estimated breeding values of sires with at least 20 daughters with phenotypes available were extrapolated for a posteriori evaluation of the observed performance. The progeny of the top 5 sires exhibited a lower incidence of hyperketonemia compared with the other cows, with only 2.16% of cows having BHB concentrations above the conventional threshold (1.20 mmol/L). Conversely, the prevalence of hyperketonemia was 5 times higher in the offspring of the bottom 5 bulls (10.55% of cows with BHB above the threshold of 1.20 mmol/L). These findings suggest that, despite the low h estimates, there is room to identify animals with low or high genetic merit for traits linked to metabolism. Therefore, selection toward healthier and metabolically resistant cows is pursuable, with MIR-predicted blood traits being potential auxiliary traits for selective breeding.
在泌乳开始时，高产奶牛通常会面临负能量平衡和代谢紊乱，如高酮血症。非酯化脂肪酸（NEFA）、β-羟基丁酸（BHB）、胆固醇、葡萄糖和尿素的血液浓度提供了有关泌乳奶牛代谢、健康和营养状况的有价值信息。近年来，牛奶中红外（MIR）光谱已成功用于预测多种健康性状，包括血液代谢物浓度，尽管模型准确性一般。事实上，MIR预测的血液参数可用于群体筛查，如果它们在群体中具有遗传性和遗传变异性，则可用于选择性育种。在本研究中，我们估计了BHB、NEFA、葡萄糖、胆固醇和尿素的遗传力（h）和遗传相关性，并利用460个牛群中9943头奶牛的表型评估了它们与意大利荷斯坦牛群体中牛奶产量和组成性状的遗传相关性。考虑了两个数据集：泌乳早期（5至35天产犊间隔期间的8277条测定日记录）和整个泌乳期（5至305天产犊间隔期间的105293条测定日记录）。血液性状的遗传力和遗传变异性在泌乳早期比整个泌乳期更大，这表明通过定制的遗传策略在过渡期控制代谢疾病发病率仍有空间。无论泌乳阶段如何，血液BHB都是遗传力最高的性状（泌乳早期和整个泌乳期的h分别为0.13和0.08），而血液NEFA是遗传力最低的性状，其h与零无显著差异。血液BHB与NEFA呈正遗传相关，而葡萄糖与BHB、NEFA和尿素呈负相关。乳脂与蛋白质的比例与BHB、NEFA和胆固醇相关，而乳糖含量与BHB之间以及体细胞评分（SCS）与BHB之间呈负相关。对至少有20头有表型后代的公牛的估计育种值进行了外推，以便对观察到的性能进行事后评估。排名前5的公牛的后代与其他奶牛相比，高酮血症发病率较低，只有2.16%的奶牛BHB浓度高于传统阈值（1.20 mmol/L）。相反，排名后5的公牛的后代中高酮血症的患病率高出5倍（10.55%的奶牛BHB高于1.20 mmol/L的阈值）。这些发现表明，尽管遗传力估计值较低，但在与代谢相关的性状方面仍有空间识别遗传价值高或低的动物。因此，朝着更健康和代谢抗性更强的奶牛进行选择是可行的，MIR预测的血液性状是选择性育种的潜在辅助性状。
