A key factor for optimal performance is ensuring cows get in calf as early as possible in the mating period. This not only relies on resumption of normal reproductive cycles in cows after calving but also normal bull fertility.Studies in Tasmania and South West Victoria have indicated a large proportion (45-50%) of prospective dairy bulls have low or very low fertility. Vibrio was also a common finding in these dairy bulls.
WHY DO BULLS BECOME INFERTILE?
The fertility of a bull is dynamic, meaning it can change from one period to the next depending on the conditions the bull is subjected to. There are many factors which can impact a bull’s fertility. These include: nutrition and body condition; the presence of disease or injury; previous and current weather conditions; genetic predisposition of fertility; dominance within the herd; other stressors, such as handling and transport.
Where possible, incoming bulls should be kept with animals of similar age and stature. Bulls coming from very different geographic and climatic environments should be relocated much earlier than those animals bought locally. Some bulls are more sensitive to stressful events which can have a negative impact on their semen quality up to 2 months after the event.
HOW DO I KNOW WHICH BULLS ARE FERTILE?
A full Veterinary Bull Breeding Soundness Evaluation (VBBSE) requires bulls to meet a set of standards for key fertility components. Passing these components increases the probability of the bull being fertile. Bulls should be tested 1 to 2 months before use to assess fertility.
THE COMPONENTS OF BULL FERTILITY TESTING ARE:
- Scrotum – Scrotal circumference (cm) and tone/resilience. The minimum values depend on breed and age of the bull.
- Physical examination – This evaluation will identify structurally unsound bulls in the head, legs, feet, sheath and penis.
- Semen – Crush-side assessment indicates that the semen is within normal range for motility, colour, progressive motility (%) and is suitable for laboratory evaluation. A new technology allowing more accurate, consistent and rapid semen analysis is the iSperm iPad app. This allows our vets to assess the concentration and motility of semen crush-side via 300x magnification, 1080p HD video and 5MP images.
- Morphology – Semen examination of the individual sperm cells using high power magnification to ensure minimum standards for normal function are achieved.