Herd reproductive performance is an important component of efficient milk production. Australian studies have identified several important factors that drive herd fertility. One of these is bull performance.
Where bulls are used in a mating program, either alone or as a follow up to an AI period, we need to ensure that we have enough bulls for the number of cows and that these bulls are fertile and capable of serving.
The Veterinary Bull Breeding Soundness Examination (VBBSE) is a standardised, repeatable procedure that is designed to classify bulls in to 3 groups: Pass, Qualified pass and Fail. It is a measure of the risk that the bull can serve a cow and deliver good quality semen.
Pass: No risk factors for reduced fertility were identified
Qualified pass: Not all attributes were normal but they did not automatically preclude the use of the bull
Fail: The bull has a significant risk of reduced fertility
What are the components of a VBBSE?
- Physical examination: This looks at the feet and legs, testes, penis, internal reproductive organs, locomotion, eyes and mouth. Abnormalities detected include lameness, penile and testicular abnormalities, small testes, poor conformation, undershot jaws and seminal gland inflammation.
- Crush side semen: This involves the examination of a semen sample either with a microscope or with our new iSperm unit. This is an iPad combined with a device and software that allows an analysis of sperm concentration and a very accurate estimation of motility.
- Semen morphology: Examination of the semen by an accredited morphologist determines the proportion of normal semen and classifies the abnormal sperm into various types. This determines if the semen is capable of fertilising an egg.
- Vaccination and BVDV testing: Bulls are vaccinated with Vibrio vaccine if not already done and an ear notch is tested to ensure that the bull is not a carrier of BVDV (aka Pestivirus).
Abnormal sperm under the microscope!
What does the science tell us?
Andy Hancock completed a comprehensive study of bull performance in our district which allowed him to publish 2 papers in the Journal of Dairy Science.
Prior to joining, Andy examined 256 bulls: 70 virgin bulls and 186 mature bulls. Of the 70 virgin bulls, 8/70 (11.4%) failed (4 failed on semen morphology, 1 failed on crush-side semen examination, 2 on physical, and 1 on physical and crush side semen). Of the 186 mature bulls 42/186 (22.6%) failed (50% for poor sperm quality and 50% for physical defects).
In summary:
- 1/10 virgin bulls failed and half of these were due to semen problems.
- 1/5 mature bulls failed and again, half were due to semen problems.
In this study only 7 herds had not vaccinated their bulls with Vibrovax. In these herds the bulls were tested and in 2 of these herds we isolated vibriosis. This reinforced our advice that all bulls should be vaccinated against Vibriosis
One bull was found to be a Pestivirus PI. While the incidence of this was low, the potential impact is very high: as PIs continually shed the virus, they will infect any naïve heifers or cows and this could have serious impacts on their reproductive performance. We continue to recommend this test (an ear notch) and each year we find a small number of positive bulls.
It is important to note that just because a bull passes a VBBSE, it does not mean they will pass subsequent examinations (and vice versa).
Conclusion:
A reasonable proportion of herd bulls have measurable abnormalities that significantly increase the risk that they will contribute to reduced herd reproductive performance.
There is a sound argument that mature bulls should have a complete VBBSE including semen morphology. Virgin bulls have a lower rate of abnormalities but to find all of these, semen morphology is required. VBBSE are particularly useful if:
- The bulls are very expensive
- Previous reproductive performance from a previous mating indicates questionable bull performance
- Mating is taking place at out paddocks where bulls cannot be easily observed
A VBBSE does not remove the need to maintain the standard recommended bull fertility performance risk management:
- It is still important to have enough bulls, 1 per 30 cows (+ one extra). Never rely on just one bull!
- Observe working bulls regularly and identify and treat any lameness issues. Blocking bulls prior to joining can reduce hoof wear and tear
- Only mix bulls of similar age that have been run as a group for a while before being used for mating
- All bulls should be vaccinated against Vibriosis
- Pestivirus testing by ear notching bulls is a relatively inexpensive way to reduce potential serious loss
