Longitudinal microbiological evaluation of subclinical non-aureus staphylococcal intramammary infections in a lentivirus-infected dairy goat herd.

The objectives of this study were to 1) correlate pre-partum teat skin colonization with non-aureus staphylococcal (NAS) intramammary infection (IMI) in early lactation, and 2) evaluate infection dynamics of subclinical NAS IMI in goats during lactation in a small ruminant lentivirus-infected herd. Pre-partum teat skin swabs (41 goats, 82 halves) and post-partum half-level milk samples (106 goats, 203 halves) were collected at various intervals starting at ≤10 days in milk (DIM) until ≥120 DIM. Teat skin colonization and IMI were defined by culture and strain-typing. The association between the pre-kidding udder-half teat skin sample status and early lactation IMI status for a given species was investigated using McNemar's exact test or logistic regression. Time to IMI elimination and time to new IMI were evaluated by discrete-time survival analysis. Halves with S. caprae isolated from teat skin prior to kidding had increased odds of S. caprae IMI ≤ 10 DIM. Time to IMI elimination varied as a function of NAS species. Intramammary infections detected >10 DIM had a higher hazard of elimination (hazard ratio [HR] 5.6, 95% CI 2.8-11.2) than IMI detected ≤10 DIM. The presence of an IMI in the contralateral half was associated with a higher hazard of new IMI (HR 2.1, 95% CI 1.3-3.4) in an uninfected half. Further studies on interventional strategies targeting early IMI and IMI caused by persistent species are warranted.