Genetic association between somatic cell score and milk lactose in early-to mid-lactation of first calving fleckvieh cows

Abstract

The present study aimed to assess genetic correlations of milk lactose (percentage and yield), lactose to fat ratio and lactose to protein ratio with somatic cell score (SCS) in the first half of lactation, the period with the highest risk of mastitis in cows. More than 35,000 first lactation records from Austrian Fleckvieh breed were available for this purpose. A linear animal model was adopted for the genetic analysis, with inclusion of age at calving and year-month of calving as fixed effects, and additive genetic animal, herd-year of calving and residual as random effects. The average SCS in the first 150 days in milk was low (1.53 ±1.29) compared with values reported in literature for other breeds in first lactation. Heritabilities of lactose percentage, lactose to fat ratio and lactose to protein ratio were high, ranging between 0.65 and 0.71. According to lactose yield and SCS, their heritabilities were equal to 0.3 and 0.2, respectively. Since the focus was on the first lactation, where the heritability of lactose is reported to be the highest, these results agreed with expectations. The strongest genetic correlation was found between SCS and lactose percentage, and the weakest between SCS and lactose yield, suggesting that lactose percentage and yield have different variability at animal level and different potential roles at genetic level. Both lactose to fat ratio and lactose to protein ratio showed weak and negative genetic correlation with SCS. Further research is required to assess relations between lactose and recorded mastitis data, with the final goal of validating lactose level as udder inflammation indicator and explore its potential role in breeding programs to reduce cow’s susceptibility to mastitis.