Enhancing the efficiency of natural delivery of improved genetics into beef and dairy herds

Over the past 25 years there have been significant advances in quantitative and molecular genetics which now enable accurate selection of bulls with superior genetics for important health and production traits. The delivery of these improved genetics into most commercial beef herds and some dairy herds is via natural mating. Thus it is critically important to identify those genetically superior bulls which are most likely to be capable of efficiently impregnating the majority of females they are bred to. This approach to replacement bull selection will maximize the potential health, welfare and productivity benefits of beef, and also some dairy genetic improvement programmes. For each major component of bull fertility (anatomical normality, semen production and quality, mating ability and libido) standardized objective measures have been developed and minimum threshold values for each measure established. Population based studies conducted in North America and Australia have demonstrated that 20 to 30% of mating-age bulls are subfertile or infertile, the majority being the former. Routine reproductive examination of bulls to be used for natural breeding has not been conducted in the United Kingdom since the demise of the Milk Marketing Board and, until recently very few bulls were systematically examined prior to purchase or use