It is common for the stock bull to be put to the cows after two rounds of AI, and in the majority of cases, these repeat cows were picked up by the stock bull at the end of last year’s breeding season.
When there is a decrease in herd fertility, the finger of blame tends to focus on female reproductive management (body condition, disease, minerals, and inclement weather).
Bull fertility is often the last factor to be considered.
Despite the unquestionable importance of stock bull fertility, a thorough clinical evaluation of their reproductive apparatus is rarely performed on farms.
This fertility test, to ensure the bull is fit for purpose, is known as a Bull Breeding Soundness Examination (BBSE).
The BBSE can be performed pre-sale, after purchase/ pre-breeding, where sub- fertility is suspected during the breeding season, and occasionally post vasectomy or castration.
A physical examination, where the mouth and teeth, eyes, feet and body condition are assessed, and the heart and lungs are auscultated.
An examination of the genitals and internal sex organs; the testicles are felt and measured (there is a close correlation between testicle size and fertility).
The internal sex organs are examined by rectal examination.
The final stage of the BBSE involves visualisation of the penis, and collection and evaluation of a semen sample.
The semen sample is obtained by electro-ejaculation (EEJ) and is examined immediately, on-farm, using a microscope.
The motility of the sperm is assessed.
Stained slides are prepared for morphological examination, used to evaluate the percentage of sperm with normal anatomy.
A minimum of 70% is needed to have normal morphology.
When these three stages are complete, your vet will issue a certificate, citing any abnormalities.
The veterinary certificate does not include any testing for infectious/ contagious diseases (BVD, IBR, Leptospirosis, Salmonellosis, and Johne’s disease).
It is important to note, however, that assessment of the bull’s libido (desire to serve a cow) is not included as part of the BBSE.
A BBSE is a reliable and effective method of identifying bulls of satisfactory fertility potential, and those that are clearly unsatisfactory.
However, it is “on the day”, and a bull that is satisfactory today may become sub-fertile or vice-versa.
A normal fertile bull should be able to achieve a pregnancy rate of at least 90% in a group of 50 normal cycling, disease-free females in a nine-week period by natural service.
Essentially, this is a bull fit for purpose — to repeatedly mount and serve females with good quality semen and good semen delivery.
An infertile bull is not capable of getting a cow pregnant, while a sub-fertile bull may put some cows in calf, but will not achieve the same pregnancy rate as a normal bull.
Many studies have shown that 20% or more bulls are sub-fertile or infertile.
Factors that can influence bull fertility include; abrupt changes in nutrition/BCS loss; stress (adapting to new location); disease; lameness; and an expectancy to bull an excessive number of females.
Newly purchased bulls should be isolated, tested for infectious diseases, and vaccinated and foot-bathed upon arrival at the new farm.
During this time, young bulls should be gradually weaned off concentrates, and introduced to a quiet cow to gain experience.
A well-acclimatised young bull can serve 15-20 females once he has gained experience, while a mature bull would be expected to serve at least 50 females in a season.
Improving on-farm efficiencies has never been so important.
There is a huge cost benefit potential in identifying sub-fertile and infertile bulls, and in the current climate of poor milk price and increasing herd size, the bull should not be overlooked.
If you have further questions or would like to arrange BBSE, contact your vet.