Small Ruminant Research 46 (2002) 115–121 Prevalence and incidence of subclinical mastitis in goats and dairy ewes in Vermont, USA Scott McDougall a,∗ , Woody Pankey b , Carol Delaney b , John Barlow b , Patricia A. Murdough b , Dan Scruton c a Animal Health Centre, P.O. Box 21, Morrinsville, New Zealand b Department of Animal Sciences, University of Vermont, Burlington, VT, USA c Vermont Departmentof Agriculture, Montpelier, VT, USA Accepted 28 July 2002 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. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Mastitis; Sheep; Goats; Prevalence; Incidence 1. Introduction Control of mastitis and somatic cell counts (SCC) in dairy animals is aided by an understanding of the pathogens involved, the rate of new intramammary in- fection (IMI), the spontaneous cure rate and the source of infection. Defining periods of high risk of new IMI ∗ Corresponding author. Tel.: +64-7889-5159; fax: +64-7889-3681. E-mail address: smcdoug@anhealthc.co.nz (S. McDougall). will aid in development of management practices that may reduce new IMI. Coagulase negative staphylococci (CNS) are the most prevalent pathogens of the mammary gland of sheep and goats (Poutrel and Lerondelle, 1983; Maisi et al., 1987; de la Cruz et al., 1994; Fthenakis, 1994). However, the dynamics of CNS IMI of goats and sheep are not well documented. Many studies have defined prevalence of individual pathogens at one point of lac- tation. Prevalence of IMI is dependant on the rate of new IMI (i.e. the incidence of infection; Thrusfield, 0921-4488/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4488(02)00191-8