Chris Gregory BVSc MRCVS, Molecare Veterinary Services
Spring is here, and it will not be long before sucklers have a calf at foot and seasonal dairy herds are overrun with new-borns. The benefits of a concentrated calving period relate to more efficient animal management, e.g. batch calf husbandry, parasite control, vaccination and nutritional management, hopefully culminating in uniform groups of weaned calves and finishers. To maintain a tight calving pattern the coming months are the most important on the calendar.
With Planned Start of Mating (PSM) around the 1st May onwards it’s important to ensure both sides of the party are prepared. Solid heat detection and planned fertility visits will keep the cows on target. However, fertility targets are also dependant on the bull: if he isn’t ‘firing on all cylinders’ all that effort can be in vain.
Fertility Targets depend on bull power:
≥90% of the herd calve within a 9 week period
Bull should get >90% of 50 normally-cycling females pregnant within 9 weeks – >60% of these in the first 3 weeks
>95% calves weaned
Seasonal dairy herds will also require the bull/team of bulls to be ready for their own six-week window of opportunity post AI.
6 week in-calf rate >70%
Empty rate (following 12 week mating period) <9%
3 week submission rate >85%
Conception rate- 60% of all serves holding
Up to 20% of bulls can be sub-fertile at any one time. Rarely is a bull completely infertile, but sub-fertility will lead to lower conception rates and hence more spread out calving periods. Sub-fertility can result from many factors, e.g. physical inability, disease status, nutrition status and semen quality. The only way to check for subfertility is a pre-mating evaluation. Sperm cell re-generation can take up to eight weeks from the initial problem. To allow sufficient time for rest and recovery, we would suggest a bull breeding soundness exam be carried out at least 10-12 weeks prior to PSM. A thorough physical/clinical exam is usually enough to flag up the majority of problems, and covers the following checks:
Nutrition & Body Condition
Over-conditioning of the bull can lead to temporary testicular degeneration and poor semen quality. He will soon be too busy to take care of his nutritional requirements and will need to carry good condition into the fertility block. Ensure you meet his mineral requirements.
Legs & Feet
One of the biggest causes of poor service rates is bulls going lame on turn out with the herd. Feet used to a straw bed will need an adjustment phase to toughen up on hard ground/concrete/cow tracks. This is impractical in most situations so be prepared with plenty of reserves and interchange/rest bulls as soon as required.
‘Post-Leg Syndrome’ – straight hocks can lead to premature degenerative joint disease in the hind limbs. Osteoarthritis can be a problem with rapidly grown yearlings with problems being linked to growth rates in excess of 1.3-1.7 Kg/day.
Feet should be trimmed as a routine, annually, or as soon as lameness is detected. Walk your bull up now to detect problems. Lesions caught early require little effort to fix but allow them to linger any longer than two weeks and resolution is far more difficult. Do not to assume a course of antibiotics will sort it, horn lesions need addressing sooner rather than later.
Eyes, Ears, Mouth (Senses)
All the libido in the world counts for nothing if he can’t see/hear or eat enough. Vision tests are simple so ask your vet. Watch him eat to check each mouthful is chewed and swallowed without obstruction, ensuring he is not impacting his cheeks with cuds or quidding.
You are looking for an even smooth, straight, penis, easily extruded and retracted within the sheath. Urine flow should be unremarkable. Testicles should be symmetrical with mobility within the scrotum with no swellings or signs of inflammation. Scrotal circumference should be 30cm in 12-15 month bulls, increasing to 34cm+ at > 24 months old. If you have not noticed any attempted mating behaviour, try an observed mating with a bulling cow. This gives you the chance to check his libido and physical ability.
The final stage of the examination requires collection of a sperm sample for analysis under a microscope. This phase of the exam will rule out any unseen inadequacies and confirm if the bull is indeed ‘firing on all cylinders’.
If you have any concerns about your bull’s breeding ability speak to your vet as soon as possible.