Management and Economics of Natural Service Sires on Dairy Herds

Abstract

To eliminate inefficient heat detection many dairies use natural service (NS) bulls. The perception is that pregnancy rates improves when NS is used because more cows are detected in true estrus and serviced; that is the intensity and accuracy improves in the herd. A 1984 survey of dairy herds in Florida showed that 50 per cent used AI, 38 per cent used a combination of AI and NS, and the remainder used mostly NS.³ A Pennsylvania study involving 329 dairy farms, evaluated the method used in breeding heifers; 11.2 per cent bred their heifers once with AI then used a bull, 8.5 per cent bred their heifers twice with AI then used bulls and 20.7 per cent bred their heifers with bulls only.⁴ Estimates from large dairy herds in Florida and Texas indicates that the use of NS is still widespread particularly in dairy herds employing a rotational grazing management. Dairy herds that use NS bulls usually do not raise replacement heifers, the genetic balance of the herd can be maintained by purchasing replacement heifers from breeders who are using AI with semen from proven bulls.

The use of NS can reduce the negative effect that people can have on reproduction by eliminating errors in estrus detection. However, when the equation of reproduction is re-examined using NS, it becomes apparent that the fertility of the bull and his ability to service cows that are in estrus greatly determines the pregnancy outcome. Therefore, in order to adequately exploit the use of NS in dairy herds, proper selection and management of these bulls should be included in the overall herd health program of the dairy. In addition, to prevent the disastrous economic consequences of sub-fertile bulls, periodic evaluation of their reproductive performance must be performed.