Basic Facts of Mastitis in Dairy Animals: a Review

Mastitis continues to be the most costly disease of dairy animals. Field surveys of major livestock diseases in Pakistan have ranked mastitis as number one disease of dairy animals (Cady et al., 1983; Khan et al., 1991). In Nili-Ravi buffaloes, mastitis shortens lactation period of each animal by 57 days on an average and reduces 438 kg of milk per lactation (Cady et al., 1983). In addition, mastitis impairs the quality of milk and milk products (Philpot, 2003; Ullah, 2004). Statistics of current losses in Pakistan due to mastitis are not yet available, but in Punjab alone, the total losses caused by clinical mastitis amount to Rs. 240 millions per year (Chaudhry and Khan, 1978). These occur through discarded milk, reduction in milk yield, premature culling of animals and replacements. The losses caused by clinical mastitis do not take into account those caused by sub-clinical mastitis which is less obvious and may only be detectable by measuring the milk’s somatic cell counts (SCC). Clinical mastitis is characterized by sudden onset, swelling, and redness of the udder, pain and reduced and altered milk secretion from the affected quarters. The milk may have clots, flakes or of watery in consistency and accompanied by fever, depression and anorexia. The sub clinical mastitis is characterized by having no visible signs either in the udder or in the milk, but the milk production decreases and the SCC increases, having greater impact in older lactating animals than in first lactation heifers. A negative relationship generally exists between SCC and the milk yield. Milk from normal uninfected quarters generally contain below 200,000 somatic cells /ml. A value of SCC above 300,000 is abnormal and an indication of inflammation in the udder. There is a plethora of evidence that the dairy cow milk has a natural level of 100,000-150,000 somatic cells/ml and higher SCC indicates secretory disturbance (Hillerton, 1999). According to Shearer and Harris (2003), subclinical mastitis is important due to the fact that it is 15 to 40 times more prevalent than the clinical form (for every clinical case of mastitis there will be 15-40 sub clinical cases), it usually precedes the clinical form, is of longer duration, difficult to detect, adversely affects milk quality and production and constitutes a reservoir of microorganisms that lead to infection of other animals within the herd. Losses due to mastitis may even be higher in Pakistan than developed countries because mastitis prevention practices like post milking dipping of teat and dry period therapy are not so far being carried out in Pakistan (Shakoor, 2004).