Relationship of somatic cell count with milk yield and composition in the herds of Black-and-White cattle

摘要

Infectious diseases adversely affect livestock production and animal welfare The costs of diseases are estimated as 17% of'turnover in the developed world, There aie many documented examples of genetic differences between animals in resistance to specific diseases 01 tolerance of infection (2). Despite a large number of well-documented examples of genetic variation in resistance, there are surprisingly few cases of structured commercial breeding programmes for disease resistance The best-known examples are for nematode resistance in sheep, tick resistance, mastitis andMarek's disease Breeding programmes for nematodes are under way in New Zeeland, Australia and UK; tick resistance is an integral part of cattle breeding programmes in subtropical Australia; mastitis resistance, either in terms of clinical cases of mastitis or reduced somatic cell count, is incorporated into many dairy cow and sheep breeding programmes; Marek's disease resistance is a feature of modern chicken breeding (2).