Lemal Pauline, Schroyen Martine, Gengler Nicolas
TERRA Teaching and Research Center, University of Liège, Gembloux Agro-Bio Tech (ULiège-GxABT), 5030 Gembloux, Belgium.
TERRA Teaching and Research Center, University of Liège, Gembloux Agro-Bio Tech (ULiège-GxABT), 5030 Gembloux, Belgium.
J Dairy Sci. 2025 Sep;108(9):9930-9945. doi: 10.3168/jds.2024-26227. Epub 2025 Jul 9.
Somatic cell count is widely used for large-scale udder health monitoring and remains a proxy for mastitis incidence still used in many genetic evaluation systems. This trait and its log-transformation, SCS, are thus also available to study the effect of heat stress on mammary gland health. Currently, a new trait called differential somatic cell count (DSCC), which represents the percentage of neutrophils and lymphocytes in the total SCC, is increasingly phenotyped simultaneously with SCC. By combining information, SCS and DSCC could more closely reflect the direct trait than SCS alone, providing a better proxy for mastitis incidence including during heat stress events. On this basis, the first objective of this study was to evaluate the interest of DSCC for heat stress assessment with a focus on mammary gland health with SCS as comparison. Additionally, the interest of both traits for genetic evaluation of udder health thermotolerance was explored. Because studies providing basal genetic parameters for DSCC are still rare, they were also estimated in this study. To do so, a random regression model on DIM was performed considering each parity as a different trait. For both SCS and DSCC, similar averaged daily heritability (0.10 to 0.11 for SCS and 0.11 to 0.14 for DSCC) and repeatability (0.61 to 0.64 for SCS and 0.54 to 0.63 for DSCC) were obtained. Moderate averaged daily genetic correlations were also estimated between SCS and DSCC (0.43 to 0.55). From the residuals of the same model, average residual responses with temperature-humidity index (THI) were studied. The results showed that DSCC reaction in mean and in variance with high THI was stronger than SCS. In addition, the reaction with increasing THI seemed to be inconsistent between lactation numbers for SCS conversely to DSCC. In this way, DSCC presented more relevant characteristics than SCS to discriminate thermotolerant and thermosensitive cows for udder health. However, for general heat stress detection, udder health traits seemed not to be the most adapted biomarkers. Low heritability (0.02 to 0.03 for SCS and 0.03 to 0.04 for DSCC) and repeatability (0.12 to 0.18 for SCS and 0.20 to 0.26 for DSCC) values were also obtained for SCS and DSCC newly defined thermotolerance traits.
体细胞计数被广泛用于大规模乳房健康监测，并且在许多遗传评估系统中仍然是乳腺炎发病率的一个替代指标。因此，这个性状及其对数转换值——体细胞评分（SCS），也可用于研究热应激对乳腺健康的影响。目前，一种名为差异体细胞计数（DSCC）的新性状越来越多地与体细胞计数同时进行表型分析，DSCC代表了总体细胞计数中嗜中性粒细胞和淋巴细胞的百分比。通过整合信息，SCS和DSCC可能比单独的SCS更能紧密地反映直接性状，为乳腺炎发病率提供更好的替代指标，包括在热应激事件期间。在此基础上，本研究的首要目标是以SCS作为对照，评估DSCC在热应激评估中对乳房健康的意义。此外，还探讨了这两个性状在乳房健康耐热性遗传评估中的意义。由于提供DSCC基础遗传参数的研究仍然很少，本研究也对其进行了估计。为此，针对每个胎次作为不同性状，在泌乳天数上进行了随机回归模型分析。对于SCS和DSCC，均获得了相似的平均日遗传力（SCS为0.10至0.11，DSCC为0.11至0.14）和重复性（SCS为0.61至0.64，DSCC为0.54至0.63）。SCS和DSCC之间也估计出了中等的平均日遗传相关性（0.43至0.55）。根据同一模型的残差，研究了与温湿度指数（THI）的平均残差反应。结果表明，DSCC在高THI时的均值和方差反应比SCS更强。此外，与THI升高的反应在SCS的不同泌乳次数之间似乎不一致，而DSCC则相反。这样，DSCC在区分乳房健康的耐热和热敏奶牛方面表现出比SCS更相关的特征。然而，对于一般热应激检测，乳房健康性状似乎不是最适用的生物标志物。对于新定义的SCS和DSCC耐热性状，也获得了较低的遗传力（SCS为0.02至0.03，DSCC为0.03至0.04）和重复性（SCS为0.12至0.18，DSCC为0.20至0.26）值。
