Abstract

Objectives: To test whether Scandinavian Red (SR) sires improve udder health (somatic cell score; SCS) in New Zealand crossbred dairy cows without compromising milk solids yield.
Materials and Methods: Herd-test records (one test day per cow) from six pasture-based New Zealand herds were analyzed (n = 5,294). All cows were daughters of Friesian x Jersey dams and were sired by Friesian (F), Jersey (J), Friesian × Jersey (F × J), or SR bulls. SCS was calculated as ln (SCC/1,000). Linear models estimated sire-breed effects on SCS, adjusting for herd, cow age group, days in milk (linear and quadratic), and milk solids (fat + protein, kg/day). Tukey-adjusted comparisons were used.
Results: Sire breed significantly affected SCS (p = 0.004). SR-sired cows had the lowest adjusted mean SCS and were significantly lower than F- and J-sired cows; F × J-sired cows were intermediate. Milk solids (kg/day) yield did not differ by sire breed (p = 0.12). Older cows, early/late lactation, and herds were associated with higher SCS.
Conclusions: Under pasture-based New Zealand conditions, using SR sires on Friesian x Jersey dams was associated with improved udder health (lower SCS) without reducing milk solids yield, supporting SR genetics as a practical option to reduce mastitis risk and antimicrobial use.

Key words: Dairy cattle; somatic cell count; udder health; antimicrobial resistance; crossbreeding; Scandinavian Red