It is easy for producers to focus their efforts and resources on female fertility within their breeding herd, resulting in the genetic selection of herd sires to be overlooked. Selection of sires on appearance alone has seriously limited the Australian beef industry rate of gain.
The Australian Association of Cattle Veterinarians have 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.
Tableland Veterinary Service offers the service of Bull Breeding Soundness Examinations (BBSE) to producers and studs by experienced and qualified veterinarians.
The BBSE was developed to standardize bull fertility testing and to provide a consistent measure of bull fertility. The evaluation requires a bull to meet a set of standards for key fertility components, which indicate whether a bull has a high probability of being fertile.
The components are:
- Scrotal circumference and tone or resilience
- Physical examination for faults in the head, legs, joints, feet, sheath and penis
- Semen analysis for motility
- Morphology (or structure of the individual sperm cells)
- Serving Ability (Not routinely carried out with Bos indicus bulls)
A summary of the five components of bull fertility in the BBSE follows:
- Scrotum - Scrotal circumference/size in centimetres where testes shape is within normal range. The minimum values depend on breed and age of the bull.
- Physical – Within the constraints of a standard examination, there is no evidence of any general physical/structural condition or of a physical condition of the reproductive tract indicating sub-fertility or infertility. This evaluation will identify structurally unsound bulls in legs, feet, sheath and general structure.
- Semen – Crush-side assessment indicates that the semen is within normal range for motility, colour and percent progressively motile and is suitable for laboratory evaluation.
- Morphology – Semen examination of percent normal sperm using high power magnification to ensure minimum standards for normal function are achieved.
- Serving – The bull is able to serve normally as demonstrated in a standard test and shows no evidence of fertility limiting defects.
Morphology - Why it is important
- Morphology in a BBSE is basically the ‘structure’ of individual sperm cells. The structural attributes that require a specialised microscope to view are frequently just as important, if not more important as far as affecting a bulls fertility.
- These attributes are important as they can affect the ability of individual sperm to move within the female reproductive tract, and the ability of sperm to fertilise an egg
- Bulls continuously produce semen within the tubules in the testicles. The testicles are about 2ºC 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 about 6-8 weeks from the start of production to when the semen is ready for ejaculation. As semen is continually produced, unused semen is excreted in the urine of all bulls.
Tableland Veterinary Service strives to improve producer profitability and productivity by promoting BBSE and reproductive performance of females. We recommended that bull buyers request a complete BBSE when sourcing bulls. It is important to note that a bull with unknown fertility (and genetic merit for fertility) is going to affect herd function and profitability well into the next decade.