SHOULD FERTILITY AND UDDER HEALTH BE CONSIDERED IN DAIRY-CATTLE BREEDING

Fertility and udder health are highly discussed topics in dairy cattle breeding. Apart from economic aspects there are also other reasons like animal welfare. From the point of animal breeding theory all economically important traits should be included in the aggregate breeding value. However, the desirable selection according to the aggregate breeding value is only superior if the economic and genetic parameters are reasonably well known. Fertility and udder health are undoubtedly traits, which can cause problems even in well managed herds. In a large survey it was found that about one third of all cows had inflammation of the genital tract and/or fertility problems (e.g. zystic ovaries, etc.) and about 13 % had mastitis during the lactation. In the literature the reported estimates of heritabilities for fertility and udder health traits vary over a considerable range, however, it is concluded that they are most likely below 0.05. Only cell count seems to have a heritability around 0.1. The estimates for the genetic correlations vary in a similar way, however, the traits are nearly always antagonistic to milk yield. The economic coefficients needed for the definition of the aggregate breeding value are discussed. It is important that the effects of changes are not counted twice. For a small population the consequences for the selection of males are investigated if the aggregate breeding value is used. As it turns out the optimal breeding schemes is almost the same as it would be if only milk yield was considered (many testbulls with relatively few daughters). That is even true if the economic coefficient for milk yield is halved and the heritabilities of fertility and udder health traits is more than doubled. Comparison of the genetic progress of the two extreme options, using information of milk yield and fertility and udder health or using only milk yield, reveals a great dependency of the difference on the economic coefficient of milk yield and on the heritabilities and genetic correlations. In the most unfavourable situation the additional use of information on fertility and udder health increases genetic progress only slightly, in other situations the increase is large. General recommendations are therefore very difficult to give. Generally the fertility and udder health traits should be systematically considered in the breeding work and at least relevant data collected for different purposes (Al data, cell count) should be utilized in a consequent manner.