Dynamic and impacts of staphylococcal intramammary infections during dairy cows’ non-lactating periods

Abstract

Staphylococcal species are common intramammary pathogens in dairy cows and can be acquired before first calving or during the dry period. This longitudinal cohort study followed primiparous and multiparous cows from five AMS-managed herds to (1) describe species-level prevalence of staphylococcal intramammary infections (IMI) around calving and dry-off, (2) estimate incidence and persistence of species across the dry period, and (3) assess their impact on early-lactation somatic cell score (SCS) and milk yield. Milk samples were collected before dry-off, after calving, and—every two weeks up to 305 DIM—for SCC and daily milk production. Species identification was performed using culture and MALDI-TOF MS. First-lactation cows had a higher prevalence of staphylococcal IMI at calving than multiparous cows. Staphylococcus chromogenes was the most common species in early lactation (10.3%) and caused a substantial rise in SCS during the following lactation, although it did not reduce milk yield. Multiple species—including S. aureus, S. xylosus, S. simulans, S. epidermidis, S. haemolyticus, and S. chromogenes—were able to persist through the dry period, and new IMI were also acquired during that time. Postcalving IMI with several species increased quarter-level SCS in the next lactation, while S. aureus and S. epidermidis IMI also reduced quarter milk yield by 1.9 and 1.7 kg/quarter-day, respectively. Overall, although many non-aureus staphylococci were common and sometimes persistent, only a few species were associated with measurable milk yield losses despite being linked to increased inflammation.