The objective of this study was to consider different and alternative methods of using somatic cell count (SCC) data recorded according to the Italian official milk recording system, estimating its genetic parameters and the correlations with the yield traits (milk, fat, and protein) in the Rendena breed. The SCC traits defined for genetic evaluation were somatic cell score, log of the total daily SCC (LTSCC, i.e., SCC multiplied by daily milk yield) individually recorded in a day of official control, and 3 different thresholds (≥80,000, ≥150,000, and ≥400,000 cells/mL) for somatic cells. A total of 187,052 test-day monthly records of milk, fat, and protein yields and SCC belonging to 11,718 cows were used to estimate heritability and genetic correlations between SCC and yield traits via a bi-trait repeatability test-day model using a Bayesian approach. The heritability values estimated for the threshold traits ranged from 0.036 to 0.065, less than those observed for monthly somatic cell score and LTSCC traits that were equivalent to 0.088 and 0.103, respectively. Higher genetic correlations were estimated between LTSCC trait and all productive traits (0.379 for milk, 0.240 for fat, and 0.370 for protein). The other SCC traits considered have shown low or almost null genetic correlations with the productive traits (from 0.008 between fat yield and SCC ≥150,000 cells/mL to 0.234 between protein yield and SCC ≥400,000 cells/mL) and almost all estimates included zero in the 95% highest posterior density region interval. These results indicated that genetic selection for milk, fat, and protein production negatively affects the LTSCC content and SCC ≥400,000 cells/mL but does not negatively influence the other somatic cell and threshold SCC traits in the Rendena breed. However, the complete framework of genetic relationships of SCC with all traits under selection should be considered when deciding on the possible inclusion of SCC in the breeding program of this small cattle population.

这项研究的目的是考虑使用根据意大利官方牛奶记录系统记录的体细胞计数（SCC）数据的不同和替代方法，估算其遗传参数以及与产量性状（牛奶，脂肪和蛋白质）的相关性在Rendena品种中。为遗传评估定义的SCC特征是体细胞评分，在官方对照的一天中单独记录的每日总SCC（LTSCC，即SCC乘以每日牛奶产量）的对数，以及3个不同的阈值（≥80,000，≥150,000，且对于体细胞，≥400,000个细胞/ mL）。总共187,052个测试日的每月牛奶，脂肪和蛋白质产量和SCC记录，分别属于11，通过使用贝叶斯方法的双性状重复性试验日模型，使用718头母牛评估SCC和产量性状之间的遗传力和遗传相关性。估计的阈值性状的遗传力值在0.036至0.065的范围内，比每月的体细胞得分和LTSCC性状分别等于0.088和0.103的观察值低。估计LTSCC性状与所有生产性状之间具有较高的遗传相关性（牛奶0.379，脂肪0.240，蛋白质0.370）。所考虑的其他SCC性状与生产性状的遗传相关性较低或几乎为零（从脂肪产量和SCC≥150,000细胞/ mL之间的0.008到蛋白质产量和SCC≥400,000细胞/ mL之间的0.234），几乎所有估计值都包括零。最高后密度区域间隔为95％。这些结果表明，对牛奶，脂肪和蛋白质生产的遗传选择会对LTSCC含量和SCC≥400,000个细胞/ mL产生负面影响，但对Rendena品种中的其他体细胞和阈值SCC特性没有负面影响。但是，在决定将SCC包括在此小牛群的育种程序中时，应考虑SCC与选择的所有性状的遗传关系的完整框架。