Effect of Somatic Cell Count on Fertility and Milk Yield Traits During Different Lactation Periods in Holstein Cows

Abstract

The aim of this study was to evaluate the effect of somatic cell count (SCC) variation on fertility [days open (DO), number of inseminations per pregnancy (NIPP), calving interval (CI) and gestation length (GL)] and milk yield traits [daily milk yield (dMY), lactation length (LL), lactation milk yield (LMY) and 305-days milk yield (305-dMY)] during early (< 100 d), mid (100-200 d) and late lactation (> 200 d). This study was conducted with primiparous and multiparous Holstein cows at a commercial farm having an approximate herd size of 260 heads in Kırşehir, Türkiye. A total of 107 Holstein dairy cows on the farm were selected. Milk samples were collected once a month during morning milking between 30 and 240±15 d of lactation. The somatic cell counter (DCC, DeLaval, Tumba, Sweden) was used to assess SCC (cells/ml). SCC levels were categorized into three groups (< 100 × 10³ cells/mL, 100-200 × 10³ cells/mL and > 200 × 10³ cells/mL). Cows were divided into three groups according to parity: Cows with parity 1 (first group; n = 49), cows with parity 2 (second group; n = 30) and cows with parity 3 ≤ (third group; n = 28). Parity did not influence fertility traits (P>0.05). Parity significantly affected dMY and 305-dMY, but not LL or LMY. The study found that cows with SCC < 100 × 10³ cells/mL had lower DO and CI values compared to cows with SCC 100-200 × 10³ cells/mL and > 200 × 10³ cells/mL during mid-lactation, although no statistical differences were observed in the NIPP, GL, dMY, LL, LMY and 305-dMY values. A positive correlation was observed between SCC groups and DO during mid-lactation. These findings suggest that SCC can be used as an indicator in indirect selection programs to achieve shorter DO and CI in Holstein cows.