Udder health-related traits in cow milk: phenotypic variability and effect on milk yield and composition

The milk differential somatic cell count (DSCC) has been proposed in recent years as a mean by which to better monitor the udder health status (UHS) in dairy cows. Milk DSCC is the amount of polymorphonu-clear neutrophils and lymphocytes contributing to the total somatic cell count (SCC) and can be deter-mined on a routine basis in individual milk samples subjected to official analysis. In the present study, 522 865 milk test-day records of 77 143 cows were scrutinised to identify factors affecting the variability of both DSCC and SCC in Holstein Friesian, Jersey, Simmental and Rendena cows through linear mixed models. The fixed effects were breed, parity, lactation stage, sampling season, and all the first-order inter-actions of breed. Cow and herd-test-date were considered as random. Subsequently, four UHS groups were created (1: SCC < 200 000 cells/mL and DSCC < 65%; 2: SCC < 200 000 cells/mL and DSCC > 65%; 3: SCC > 200 000 cells/mL and DSCC > 65%; 4: SCC > 200 000 cells/mL and DSCC < 65%) to compare milk yield and quality. Milk SCS and DSCC differed across lactation, parity, sampling season and breed. In particular, Simmental cows had the lowest SCC and Jersey the lowest DSCC. Depending on the breed, UHS affected daily milk yield and composition to a different extent. The UHS group 4, i.e. the one grouping test-day records with high SCC and low DSCC, presented the lowest estimate of milk yield and lactose content no matter the breeds. Our findings support that udder health-related traits (SCS and DSCC) are useful information to improve udder health at individual cow and herd levels. Moreover, the combination of SCS and DSCC is useful to monitor milk yield and composition.(c) 2023 The Author(s). Published by Elsevier B.V. on behalf of The Animal Consortium. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The milk differential somatic cell count (DSCC) has been proposed as a means to monitor udder health status (UHS) in dairy cows. The study analyzed milk test-day records of different cow breeds to identify factors affecting DSCC and SCC variability. Udder health-related traits (SCS and DSCC) were found to be useful in improving individual cow and herd udder health. The combination of SCS and DSCC is also useful in monitoring milk yield and composition.