Mastitis Control in Replacement Heifers

Abstract

Mastitis is the most costly disease of dairy cattle. This disease occurs when bacteria penetrate the teat orifice, colonize teat canal keratin, and gain entry into the mammary gland. In spite of growth inhibitory properties of keratin bacteria are able to survive in the teat canal and progress into the udder, causing inflammation. Current methods of mastitis control advocate adoption of management practices developed for mature lactating and dry cows, and include teat dipping, dry cow therapy, proper use of functionally adequate milking machines, prompt treatment of clinical cases, and culling of chronically infected animals. However, methods for controlling the disease in heifers were not contemplated in development of these management schemes. Mammary glands of heifers have traditionally been regarded as uninfected, and their mammary secretions are not examined until the first milking or during the first episode of clinical mastitis following calving. The greatest development of milk producing tissue in heifers occurs during the first pregnancy, thus mammary glands must be protected from the harmful effects of mastitis-causing bacteria to insure maximum milk production and reduce the level of infection and somatic cell count (SCC) during the subsequent lactation. This is particularly important in view of the recent decision to lower the SCC legal limit. Effective July, 1993, the new Interstate Milk Shippers' quality standard for raw milk will set the SCC limit at 750,000/ml. Thus, in addition to tightening up standard mastitis control practices in lactating and dry cows, dairymen should carefully consider a mastitis control program for heifers in attempts to conform to the new quality standard.