Checking a bull’s breeding capacity
REPRODUCTIVE performance is a key driver to profitability in all beef breeding enterprises.
The current strong cattle market is providing the perfect opportunity to assess and fine tune the fertility of your herd.
Producers can often spend a lot of effort in selecting replacement females and frequently become so focused on the environment of their production system they fail to place the necessary emphasis on genetic selection of herd sires.
The herd sires set the direction of profitability for many years to come, so careful selections need to be made to achieve significant genetic progress.
The Australian Association of Cattle Veterinarians has determined that fertility is the ability of a bull to achieve, by natural service, a pregnancy rate of 60% and 90% in 50 normally cycling females within three and nine weeks of mating respectively.
The Veterinary Bull Breeding Soundness Exam (better known as BULLCHECK) was developed by the ACV to standardise bull fertility testing and to provide a consistent descriptor of bull fertility along with appropriate certification.
Cattle veterinarians must become accredited to be able to perform this.
BULLCHECK provides a standard of assessment for veterinary evaluation of the various reproductive traits important to beef producers and indicates whether a bull has a high probability of being fertile.
This evaluation is conducted prior to sale and details the identification of the sire, date and location where the evaluation was conducted, the assessments made and relevant disease information.
It is purely an evaluation of a range of measures on that date on which it was done and does not provide any guarantee or imply the number of calves the bull will sire in either single or multiple sire matings.
The five components assessed during BULLCHECK include:
■ Scrotal circumference (cm) and tone or resilience.
■ A general physical examination including head, legs, joints, feet, sheath, upper reproductive tract and penis.
■ Collection and assessment of a semen sample for motility.
■ Laboratory examination of sperm morphology.
■ A serving assessment to evaluate libido and mating ability.
This BULLCHECK data is then transferred into the Bull Reporter software, where individual or group certificates can be produced.
The resultant certificates should be sought out by bull buyers when choosing between bulls as they also provide details of aspects of the evaluation that cannot be seen in the live animal, for example percentage normal spermatozoa and conformational detail.
Can we examine and categorise the semen produced by a bull?
Yes. Many breeders will be aware that upon the collection of semen either by electro-ejaculation or rectal massage, semen is examined crush-side for colour (no blood or urine staining allowed) and density of spermatozoa, which is ranked on a one (clear to cloudy) to five (thick creamy colour) basis.
In addition, when using low-power magnification, the amount of swirl or vigorous swimming motion of all the spermatozoa is scored on a one (no swirl, generalised flickering of individual sperm only) to five (fast distinct swirl with continuous dark waves) basis.
Once completed, the percentage of individual sperm that are swimming forward freely and independently is recorded.
This assessment is a compulsory measure of fertility to meet BULLCHECK standards.
Based on extensive research, the ACV has determined that a threshold of 30% progressively motile sperm is a pass on a BULLCHECK for a bull used in a multi-sire herd and 60% progressively motile sperm in a single-sire herd.
Understanding the morphology and why it is important
The final evaluation of the semen is the percentage of individual spermatozoa that are structurally normal – the morphology.
Morphology is frequently just as important, if not more important, as far as affecting a bull’s fertility.
To test for morphology, a sample of the semen collection is placed in a small tube with a special diluent and sent to an accredited morphologist.
The morphologist will examine 100 individual spermatozoa and report the percentage of normal sperm and the percentage of abnormalities.
Unlike the female that has her quota of eggs at the start of life, the bull is continuously producing semen within the tubules in the testicles.
The testicles are about two degrees cooler than body temperature.
Between the head, body and tail of the epididymis there is a long tube for storage and maturation of the spermatozoa produced.
This production pipeline takes six to eight weeks from the start of production to when the semen is ready for ejaculation, therefore semen results can fluctuate over time.
NO BULL: Reproductive performance should be a key consideration.