Fertility plays a significant part in ensuring the profitability and efficiency of a herd and so should be actively managed. Within a dairy herd in particular, poor breeding success rates can lead to increased costs and reduced profits, with loss of milk production, loss of milk yields from mature animal culling, high veterinary costs and increased AI costs, not to mention the potential loss of valuable genetics. Here we look at natural service management to ensure good breeding rates within a herd.

The importance of sire selection

Difficult calving and possible unsuccessful breeding can be reduced by selecting the correct sire for your requirements. For a beef herd, it is important to consider Estimated Breeding Values (EBV), and for a dairy herd, you should pay particular attention to the PTA range. If breeding replacement heifers, Profitable Lifetime Index (PLI) will also play a part in ensuring good production and fitness. The bull should be chosen for its size so that it is able to service the females easily, and is neither too large or too small.

Ensuring breeding readiness for optimum fertility

Many herds in the UK have a stock bull which is introduced to improve breeding success rates and to supplement any AI programme in use. The bull needs to be managed to ensure that it is fit for the breeding work required of it, and so approximately eight weeks before the breeding programme starts the bull should be examined to check that it is at peak fitness. This examination should include collecting a semen sample to look at motility and sperm quality, inspection of the testicles to check for any abnormalities and a scrotal measurement taken to ensure it falls within the recommended circumference guidelines. It is believed that up to 20 percent of natural service bulls have some degree of infertility and a further 10 percent are sterile.

Health checks

Bulls being introduced to the herd, whether hired or bought in, pose a health risk to the other animals and so it is vital that the health status of a bull is checked before introduction. If there is no confirmation of health then you should ask a veterinary surgeon to do a blood test or sheath wash to detect any disease that the bull may be carrying. The bull should also be scored for mobility to ensure the soundness of its legs and feet, it should be vaccinated against Leptospirosis and BVD and it should be treated for afflictions such as lungworm, fluke and worms.


Bulls should have a body condition score of between 2.5 – 3 when they are put to work and this scoring should be done about eight weeks before so that any remedial action can be taken to get the bull in the correct condition. Falling outside of this score can result in impaired libido and a possibility of reduced semen production and poor fertility. Over or under-scoring on body condition can be managed by dietary changes where necessary but these should be introduced gradually. Further investigations are needed if the score is low to check for health issues that may be caused by a parasitic burden or disease.

The importance of ongoing fertility monitoring

You should monitor your working bulls throughout the breeding cycle to check for body condition and continued mobility and also for any other physical issues. If you have more than one bull servicing the herd, it may be prudent to rest the animals, in turn, to ensure that good condition is maintained. With a younger bull, it should only be required to service 15 – 20 cows, while more mature bulls are able to service up to 40 cows without experiencing an adverse effect on fertility.