The cow’s only job is to produce a calf, you must ensure she is served by a sound, fertile bull which will get her pregnant. About 70% of the cow’s annual feed intake is solely for maintenance, and if she does not produce a calf each year this feed is wasted. Therefore before beginning mating check the bull for breeding soundness. This is particularly crucial in a fully recorded herd where you are practising single sire mating.
Single Sire Mating
To identify superior sires in a performance recording scheme single sire mating is essential to establish the essential link between a sire and his progeny. In order to get a fair assessment of different bulls’ performances you must practise representative mating and progeny testing. Once you have identified superior sires the key to rapid genetic progress is single sire mating to top performing breeding cows.
The normal ratio is one bull to 35 — 40 cows, but where the bull is proved sound for breeding one bull to 55 — 60 cows is acceptable. A high libido bull with a large scrotal circumference has the capacity to successfully mate up to 85 cows. But the ratio does depend on how tightly the cows are cycling. In the extreme situation (i.e. synchronised cows) the ratio should be no more than ten to one.
One factor influencing this is the size and terrain of the mating paddock. Ideally it should not be too large and be reasonably flat so the bull does not use too much energy moving from cow to cow. It should have adequate feed and water supplies and the fences must be in good condition.
Fitting the bull with a chinball harness, so you have a visual check of which cows have been mated and when, is a useful management practice. This enables you to mob cows according to projected calving dates, and to cull those not marked. Make sure the chinball harness is strapped onto the bull’s head correctly, that the straps are neither too tight nor too loose — trial and error is the only way to establish this, and that there is plenty of ink in the harness. Be aware a few bulls leave very little harness mark.
Bulls are generally left out for eight to ten weeks, but two-thirds of the herd should have been mated in the first six weeks. Check regularly that the bull is working. He may have injured himself mounting and if so will need replacing.
Working from the latest herd summary sheet, enter into the field notebook all the cows to be joined. (In the printout order or in mating groups, according to your preference). Enter the bull for each mating group. As mating progresses note which cows are marked and projected calving dates. When mating is complete transfer the data to herd summary sheets for updating.
Identifying cows in heat (oestrus) is the most difficult management aspect of AI. Using a ‘teaser’ (castrated) bull fitted with a chinball harness in combination with tail paint on the cows is the best identification method. Use recommended tail paint only, and remember it will not work 100% until the winter coat is lost, nor on overfat cows. Run the teaser bull with the cows selected for AI in a paddock close to the yards. Draft off marked cows once a day, either with/ or without their calves according to your preference, and bring them into the yards for insemination. Check AI has held by immediately running the cows back with the teaser bull. Alternatively, use a clean-up (entire) bull after two days. Record sires and successful AI matings in exactly the same way as for natural mating.