By Dr Charlie Blackwood
Whilst many dairy farms are busy “AIing” cows at the moment, they should consider the fertility of the bulls they will use at the end of the AI period.
Implementing a BULL FERTILITY EXAMINATION (called a Veterinary Bull Breeding Evaluation or VBBSE) on bulls prior to joining can detect bulls with low or poor fertility.
Studies in Tassie and South West Victoria have indicated a large proportion (45-50%) of prospective dairy bulls have been found to have low or very low fertility. Vibrio has also been found in the bulls. These disqualifications arose mainly from penile abnormalities, sperm defects and scrotal issues.
Bulls should be tested 1 to 2 months before use to assess fertility. Remember, semen takes over 2 months to mature, meaning any nutritional or other upset can cause issues with semen quality.
Parts of the VBBSE offered by WVC:
- Testicle and scrotum palpation and measurement
- Internal reproductive gland assessment
- Penis visualization and assessment
- Semen motility evaluation
- Semen morphological assessment – in the past this was rarely done. The recent studies show that this is possibly the most important part of the testing.
- Vibrio vaccination
Common conditions found at VBBSE:
- Small scrotal size, internal reproductive organ lesions, penile lesions including scarring, warts and persistent frenulum.
- Semen motility and semen morphology have emerged as common causes for failure in the above studies on bull testing.
- Semen morphology - semen can appear normal under the microscope but have problems which make it infertile. An expert is able to pick up many of these problems. For this reason, we send the sample off for testing.
- It is important to remember that our examination is a basic evaluation of common areas of failure. We do not routinely cover serving ability or libido testing.
You still need to be watching your bulls to ensure they mount and get the job done effectively. Bulls with sore feet, backs and penis’ will not breed to their potential – each of these may break down during the breeding season indicating bull replacement and recovery is necessary.
Bull management principles:
- Have the bulls on farm 70+ days before use
- Avoid stress (nutritional, disease, transport)
- Use bulls at 3-4 bulls/100 milking cows and rotate in teams weekly
- Test bulls prior to use Monitor bulls during mating
- All bulls should be vaccinated for vibrio. Bulls not previously vaccinated, require 2 injections 4 weeks apart and then annual boosters. Remember to give the injection under the skin.