Variation in udder health indicators at different stages of lactation in goats with no udder infection

Abstract

Mastitis is an important disease in dairy goat production. Subclinical mastitis is common in goats and is mainly caused by contagious bacteria. Several methods to diagnose mastitis in goats are available but have not all been investigated in healthy udders and at different stages of lactation. The purpose of the study was to investigate the variation in some udder health indicators at different stages of lactation in goats without intramammary infection (IMI). The udder health indicators were: somatic cell counts (SCC) measured by DeLaval Cell Counter (DCC) and estimated by California Mastitis Test (CMT), lactate dehydrogenase (LDH) activity, N-acetyl-β-d-glucoseaminidase (NAGase) activity and alkaline phosphatase (AP) activity.Milk samples from twenty-four clinically healthy dairy goats were collected on two consecutive days in early, mid and late lactation. At milking, each goat's udder half was given a CMT score before udder half milk samples were collected. The milk samples were then analyzed for SCC, LDH, NAGase and AP, and investigated for bacterial growth. Variation in udder health indicators between udder half within goat, samples between sampling days and samples between stages of lactation were investigated using multivariable mixed-effect linear regression and multivariable ordinal logistic regression models.Of the 24 goats, 18 were considered IMI negative at all samplings, 3 goats had inconclusive results for one udder half in late lactation and 3 (12.5%) had IMI positive udder halves in one or more lactation periods. Period of lactation was significantly associated with all udder health indicators with an increase in all indicators at late lactation compared to mid and early lactation. For NAGase and AP, period of lactation was significant as an interaction term with sampling day. NAGase was significantly higher on day 2 compared to day 1 in mid lactation and significantly lower on day 2 than day 1 in late lactation. AP was significantly higher on day 2 compared to day 1 in early lactation and significantly lower on day 2 than day 1 in late lactation. Moreover, for CMT there was a significant association with udder half with a higher general (over period and day) probability of higher CMT scores in the right udder half compared to the left.This study shows that SCC, LDH, NAGase and AP were all affected by period of lactation but also to some extent by sampling day and udder half. This must be considered when interpreting udder health indicators sampled at different stages of lactation.