Reproduction

Cows

• Cows will breed all year round and are not as affected by the day/night pattern (photoperiodicity) as sheep, goats and deer. But their breeding activity may be reduced in mid-winter.
• Cows start to cycle usually about 6 weeks after calving. They can show heat 3 weeks after calving but rarely conceive to this mating.
• They may show a silent heat with ovulation but no heat signs. Problems seem to be more in Holstein Friesians than Jerseys.
• The cow ovulates a few hours after the end of standing heat which has important implications for artificial insemination.
• Puberty is about 6-9months of age but some calves can show heat before that. This can be a hazard as they get pregnant and have to be aborted.
• Cattle cycle every 21 days (range 18-24) if not mated, and are on heat for about 8 hours (range 2 –12 hours).
• Signs of heat in the cow:
  • Vocalise a lot
  • Vaginal discharge – clear viscous fluid
  • Walk around a lot to find other cows
  • Cows form Sexually Active Groups (SAGs) of 3-5 cows
  • Cows on heat mount other cows
  • They stand to be mounted
  • Milk is not let down fully
• The cow is the only animal that shows this clearly-defined mounting behaviour. It is thought to have evolved to give visual signals to the bull.
• A cow that will stand for cow will not immediately stand for the bull. This has a teasing effect on the bull and while challenging his libido concentrates his semen.
• The most common method of heat detection in dairy herds is tail paint. The top of the cow’s tail is painted and the scuffed-off paint indicates if the cow has been mounted by another cow. The traffic light colour sequence is best to use.

Bulls

• Bulls will mate all year round and do not show a "rut" like sheep, goats and deer.
• Mounting and ejaculation is very quick by the bull. He grasps cow with his front legs and his whole weight is propelled on the cow. This has implications for heifer mating by large stud bulls that can damage them.
• A bull may serve a cow up to 3 times before she stops accepting him. He will hang around a served cow for a day or so in the wild. On the farm, he is generally allowed two services and is then separated. This is danger time, as the bull always reckons he wants one more and tries to get back to the cow - perhaps with a human in the way.
• Running one bull with 30-50 cows (dairy or beef) is normal. The bull is changed regularly in case he is infertile.
• Fighting among bulls is common during mating and injuries are common eg. shoulders, legs, and penis.
• In the wild Chillingham herd in UK, the king bull does all the mating until he is challenged by a young bull and they usually fight to the death for leadership.
• Bulls are regularly reared in homosexual groups so mounting and fighting behaviour is common, often leading to injury.
• Bulls may have to learn how to mate a cow, and this may take a few days to learn (and waste time) at the start of mating to learn.
• Libido testing can be done using the Blockey test. Here a cow is held in head bail and the number of mounts made by each bull is recorded. This must be done under vet supervision to avoid injury to the cow.