Short communication: Genetic aspects of milk differential somatic cell count in Holstein cows: A preliminary analysis

Abstract

The aim of the present study was to assess genetic variation and heritability of a novel indicator of udder health, milk differential somatic cell count (DSCC), which represents the percentage of neutrophils plus lymphocytes in the total somatic cell count (SCC). Furthermore, we estimated genetic and phenotypic correlations of DSCC with other milk traits routinely measured in Italian Holstein cows. Besides DSCC, testday data included milk yield, composition traits (i.e., fat, protein, casein, and lactose percentages), pH, milk urea nitrogen, and SCC. After editing, the final data set included 10,709 test-day records of 5,142 cows in 299 herds. Mean of DSCC was 62.07%, which means that macrophages were approximately 38% of total SCC. Comparing our results with the literature offered compelling evidence of the importance of acquiring information about the proportion of the different cell types in milk to better define the udder health status. In addition, our analysis revealed, for the first time, that DSCC is a heritable trait, and heritability (0.08 ± 0.02) was higher than that of traditional somatic cell score (0.04 ± 0.02). Nevertheless, heritability of DSCC is still low compared with milk yield and quality traits. Single-trait analysis within parity showed that DSCC was less heritable in primiparous than in multiparous cows, whereas bivariate analysis confirmed that DSCC and somatic cell score were 2 different traits, as their genetic and phenotypic correlations differed from unity. From a genetic point of view, the DSCC was positively weakly associated with milk yield, lactose percentage, and milk urea nitrogen, and negatively associated with pH. Our findings contributed to the understanding of the genetic background of DSCC and are a precursor to the potential use of DSCC in breeding programs to enhance cow resistance to mastitis. However, further research is needed to determine the weight this novel trait should receive in a selection program aimed to reduce udder health problems.

Combining total and differential somatic cell count to screen for mastitis

“…The average DSCC ranged from 65.2% (Brown Swiss) to 66.6% (Holstein Friesian; Table 1). Mean DSCC of Holstein Friesian observed in the present study was slightly higher than the value (62.07%) reported by Bobbo et al (2019); the difference is likely related to the fact that, after an update of the software, DSCC values corresponding to SCC < 50,000 cells/mL were set to zero in the output of the instrument (data not included in the current study). As a consequence, the average values of SCC increased slightly (Table 1).…”

“…Milk differential somatic cell count (DSCC) is a novel indicator of udder health and it represents the percentage of neutrophils plus lymphocytes in the total SCC; therefore, the percentage of macrophages can be calculated as 100 -DSCC (Damm et al, 2017). The genetic background of DSCC has been recently investigated by Bobbo et al (2019), who reported that this novel trait may be exploited in selection programs for mastitis resistance, as its heritability (0.08) was even higher than that of somatic cell score (SCS; 0.04). Moreover, information on the proportion of the different cell types in milk, in combination with total SCC, would represent a valuable asset for a more precise definition of udder health status (Pillai et al, 2001;Pilla et al, 2012;Pilla et al, 2013), and would help farmers make decisions to reduce the use of antimicrobials.…”

Combining total and differential somatic cell count to better assess the association of udder health status with milk yield, composition and coagulation properties in cattle

“…These three cell types play different roles in the immune response to mastitis and their proportion in milk varies according to the infection status of the mammary gland (Damm et al 2017). Bobbo et al (2019) demonstrated that differential somatic cell count (DSCC), which is the ratio of neutrophils plus lymphocytes to total SCC (Damm et al 2017), is potentially exploitable in breeding programmes aimed to reduce udder health problems. Furthermore, Zecconi et al (2019) established a correlation between DSCC and SCC, and defined the most accurate thresholds of DSCC to maximise the probability of correctly identifying mammary gland status in Italian Holsteins.…”

Differential Somatic Cell Count as a Novel Indicator of Milk Quality in Dairy Cows

“…Moreover, DSCC has been proposed as a useful biomarker in milk to indirectly identify mastitis, revealing inflammatory reactions also at low SCC [20], and being able to determine the stage of mastitis in combination with SCC [19]. Genetic aspects of DSCC have also been preliminarily investigated in Holstein cows [21], suggesting the consideration of DSCC in breeding programs for the enhancement of bovine resistance to mastitis.…”