Prevalence and incidence of subclinical mastitis in goats and dairy ewes in Vermont, USA

Abstract

The prevalence of bacterial isolation and the somatic cell count (SCC) of the milk from goats ( n=110 from six herds) and sheep ( n=153 from three herds) was determined at parturition and approximately 40 days later. Incidence of new intramammary infection (IMI) and the spontaneous cure rate were determined over this time period. In the goats, 27.3 and 25.5% were infected at parturition and 40 days later, respectively, while 15.0 and 9.1% of sheep were infected at parturition and 40 days later, respectively. Incidence of new infection was 0.039 and 0.034 cases/half/30 days for goats and sheep, respectively, and did not differ between the species ( P>0.2). Spontaneous cure occurred in 93.8% of sheep halves infected at parturition but only 50.0% of goat halves ( P<0.05). Coagulase negative staphylococci (CNS) were the most common isolates from both sheep and goats. Milk from bacteriologically positive halves had a significantly higher somatic cell count than halves from which no bacteria were isolated in both sheep and goats. It was concluded that bacterial infection of the mammary gland was associated with an elevated somatic cell count. Additionally, differences were detected between the species in incidence of new infection and spontaneous cure rate which resulted in a decline in prevalence in sheep, but not goats, with time postpartum.