Genetic and Economic Analysis for the Relationship Between Udder Health and Milk Production Traits in Friesian Cows‪.‬

INTRODUCTION The udder is one of the most important physiological and conformational characteristics of the cow due to its importance for milk production. Consequently, udder health is generally considered as one of the most important traits in dairy cattle production (Miglior et al., 2005). Mastitis has been recognized as a major disease affecting dairy cattle and jeopardizing both milk production and milk quality in commercial herds especially in its sub-clinical form (Schepers and Dijkhuizen, 1991; De Graves and Fetrow, 1993; Losinger, 2005). Non-management factors such as season, parity, lactation stage, breed, udder conformation, milk production, milking speed and reproductive disorders are known to be associated with mastitis (Schukken et al., 1990; De Graafa and Dwingerb, 1996; Barkema et al., 1998; Hagnestam et al., 2007; Nyman, 2007; Durr et al., 2008). Hultgren and Svensson (2009) found that 90% of the variation in mastitis risk was due to factors at the lactation level such as parity, milk yield, cow diseases, and other disturbances. In addition to the factors mentioned above, the genetic constitution and innate immune defense of a cow plays an important role in determining disease resistance in individual cows. Shook (1989) pointed out that there are several anatomical, physiological and immunological defense mechanisms in the cow against mastitis, and a large number of genes operate in these defenses. Also, nutrition can influence the cow's resistance to mastitis (O'Rourke, 2009).