Pamela L. Ruegg, DVM, MPVM, Paul Fricke, PhD & Maria Jose Fuenzalida, University of WI, Dept. of Dairy Science, Madison WI
On many dairy farms, reproductive failure and the occurrence of mastitis are two of the most common management problems. Risk factors for mastitis and reproductive disorders are similar and it can be difficult to determine the specific impact of mastitis on reproductive performance. Age of cow, heat stress, occurrence of metabolic diseases, immune suppression in early lactation and high milk yield are all associated with increased risk of mastitis and reduced fertility. However, the direct impact of mastitis on reducing reproductive performance was first noted more than 2 decades ago (Moore et al., 1991) and since that time researchers have consistently reported that mastitis can significantly reduce reproductive performance (Barker et al., 1998, Schrick et al., 2001; Santos et al., 2004a; Hertl et al., 2010). The occurrence of mastitis has been associated with reductions in the occurrence of natural estrus (Moore et al., 1991; Barker et al., 1981, Schrick et al., 20012, Santos et al., 2004a), the ability to conceive after breeding (Ahmadzadeh et al., 2009; Barker et al., 1981; Chebel et al., 2004; Santos et al., 2004a; Schrick et al., 20012) and increased pregnancy loss (Chebel et al., 2004; Hudson et al. 2012; Santos et al., 2004a).
The negative impact of mastitis on reproductive performance appears to be a consequence of the severity of the immune response to intramammary infection by bacteria (IMI). Subclinical mastitis (SM) is defined as an IMI that results in an influx of white blood cells to the udder without disruption of the appearance of milk and is usually detected based on recognition of an increased number of somatic cells in milk. Clinical mastitis (CM) is defined as an IMI that causes enough inflammation to disrupt the milk secretory process and results in the production of visually abnormal milk (with or without abnormalities in the mammary gland or systemic symptoms) (Pinzon-Sanchez and Ruegg, 2011, Ruegg et al., 2014). The occurrence of both SM (Schrick et al., 2001, Lavon et al., 2011a, Lavon et al., 2011b, Hudson et al., 2012) and CM (Moore et al., 1991, Santos et al., 2004) have been associated with reduced reproductive performance. The purpose of this paper is to review previous data about the impact of mastitis on reproductive performance and present new data that further defines the role of severity and etiology.