Somatic cell count in dairy goats II: udder health monitoring at goat and herd level.

Background: Mastitis is a costly disease affecting dairy ruminants worldwide. Somatic cell count is the most widely used tool for udder health monitoring but is highly influenced by non-infectious factors in goats. The aim of this paper was to define adjusted action thresholds of somatic cell count for the detection of goats with intramammary infections. A secondary aim was to investigate the potential of bulk milk analyses in identifying herds with udder health issues. Nine Norwegian dairy goat herds were visited five times during one lactation. Somatic cell count measurements combined with bacteriological testing were performed both at goat and herd level.

Results: Staphylococcus (S.) aureus was the udder pathogen with the strongest influence on the somatic cell count and was therefore selected as the focus of udder health control. The period prevalence of S. aureus in the included herds varied from 1 to 40%. The thresholds for identifying goats with S. aureus intramammary infection varied from 500,000 cells/mL in first parity goats in early lactation to 3 million cells/mL in goats of higher parities on pasture. A herd prevalence of S. aureus of more than approximately 10% was associated with significant bulk milk quality challenges.

Conclusions: The study defined adjusted action thresholds of somatic cell count for the detection of intramammary infections in dairy goats. The somatic cell count levels in goats with S. aureus were in most cases well distinguished from those with no or minor pathogen findings when adjusting according to parity, pasture-status, and lactation stage. The patterns of routinely measured bulk milk parameters, along with analyses of bacteriological composition, provided a rough indication of the herd's udder health status.