The Bull in Herd Fertility


Jon Goodson writes:


The influence of the bull on herd fertility in both dairy and beef herds is often overlooked with the focus being on cow infertility. If female factors and infectious disease are under control, bull fertility can make a massive difference to the efficiency and profitability of the business. Infertile bulls (incapable of achieving pregnancies) have been shown to be exceedingly rare; however I’ve certainly seen ‘duds’ in the field when doing fertility examinations. Much more common are sub-fertile bulls, with up to 20% of bulls screened falling into this bracket.


Targets for a ‘fully fertile’ bull:

  • Given a group of 40-50 cows should be able to achieve average pregnancy rate to each cycle (3 week period) of 65%.
  • Meaning in 9 weeks (3 cycles) of breeding at least 95% of cows should be pregnant.

Causes of sub-fertility

Libido – some bulls just don’t want to serve cows, possibly because of lameness or back pain, age or cow sex drive.

Physical fitness – Lameness and joint or back problems are common and should be treated urgently; these could be from fighting with other bulls or bulling injuries. Some bull aren’t fit to work either, they’re too obese or heavy to serve effectively. 

Ability to achieve intromission and deposit semen in the vagina can be caused by corkscrew penis, penile rupture, preputial tearing, prolapsed prepuce and penile papilloma.

Production of sufficient quantities of high quality semen – scrotal circumference <34cm at 24 months is highly suggestive of subfertility. Epididymitis or orchitis, infections within the testicle and sex organs can inhibit normal sperm production. Temporary reduction in sperm production or function can be caused by fever, lameness, stress and toxaemia.

Infectious conditions like Bovine Virus Diarrhoea (BVDV) or Campylobacter – these may cause subfertility in the bull and, furtherfore potentially abortions in the cows.

Pre service checklist

1) Clear disease testing and vaccination protocols on entry to the herd, including quarantine. 

2) Monitor bull body condition and ensure in good condition prior to mating period BCS 3.5-4.

3) Check for lameness and need for foot trimming around 2 months prior to breeding period.

4) Get vet to carry out routine pre-breeding examination of all bulls on an annual basis around 2 months prior to breeding period.

Monitor bull performance during the breeding period by careful observation of mating and recording cows that return to service (about 21 days later).

Fertility testing on farm

Don’t be scared of it, we do it pretty regularly as a practice, all we need is a ‘good solid crush’ to restrain him (they don’t typically like it very much, understandably) and a work surface to put a microscope on. It’s pretty quick, taking around 25 minutes per bull and really can put your mind at rest that your bulls are capable of doing their purpose and not costing you time and money. If any of the above has you interested or now you’re doubtful about one of your bulls, please don’t hesistate to get in contact with a member of the veterinary team.