8.0 ACHIEVING THE BEST BREEDING EFFICIENCY
It is possible for a cow to produce a calf every year. The time between successful mating and birth of the calf is about nine months. Once the calf is born, it may take one to two months for a cow which is well fed and in good condition to return to breeding activity and accept the bull. A return to oestrus sometimes occurs one month after calving, but breeding activity and a successful joining at two months post calving is quite common. A cow will accept the bull at intervals of about 18 to 21 days until she conceives.
It will take about nine months from the time she is successfully mated until she delivers a calf.
The longer a cow takes to become pregnant again after having calved, the fewer calves and the less milk she will produce in her lifetime and the less money she will generate through the sale of milk and calves. In general, a local type cow can be first bred at about 21 months of age, she will deliver a calf nine months later, and she will remain productively active until she is about seven or eight years of age.
Some cows will of course live longer and produce more calves than this, but from the age of about seven years onwards they begin to lose reproductive efficiency and the time between their calves becomes longer. Their place in he herd should then be taken by new heifers which produce calves at the faster reproductive rate of young animals.
The table below shows the production of two cows with different reproductive efficiency. Both are assumed to produce about 1,500 litres of milk per year. One is mated efficiently every eleven months whereas the other produces a calf every 14 months. It is clear that the cow which produces a calf every year has a great production advantage over the cow which produces a calf at a longer interval.
The factors which determine whether a cow will breed efficiently are:
·the feeding of a heifer until she reaches breeding age
·the availability of a bull at the time the cow is ready to be bred
·whether a cow is being well fed or not - poorly fed cows do not cycle well,
·the presence of reproductive disease in the herd
A heifer will come into breeding activity when she is heavy enough, not when she is old enough. So if you do not feed the young heifer well when she is under twelve months old she will not grow quickly and will be delayed coming into breeding activity until the right weight is reached. The correct first breeding weight is different for all breeds of cattle, but all heifers must be well enough fed to reach this weight regardless of breed.
A bull must be available to provide mating services to a cow starting from about four weeks after she has delivered a calf. A failure to join when she first comes into season means the loss of some of her lifetime production. Therefore it is important to have a bull available to join with the cow starting from about three weeks after she has delivered a calf
Some services do not result in conception the first time. Therefore it is also important to observe and have the bull available for joining with the cow commencing every 18 days from the last joining period, even if she was served the last time. When (from records you should keep) you know the date she should come into season again, by adding 18-21 days to the date of her last service, keep the bull available for about four days from that date until she is mated again, or she fails to return to season, indicating that she may already be pregnant.
If a cow is poorly fed after delivering a calf, she is unlikely to come into breeding activity until she again begins to put on weight. She should be well fed, particularly for the two or three months of the dry period before she calves again, as well as during the first three to four months of her lactation.
Reproductive diseases such as Vibriosis or Trichomoniasis will stop your cows from conceiving for several months, even after they have been mated by the bull several times. If you notice from your breeding records that the cows are repeatedly returning to oestrus after joining, particularly if you notice that some cows are also aborting, you should call the veterinarian to examine the herd for the presence of these diseases.