|
In the last article, we addressed the importance of the voluntary waiting period, as well as the economic benefit of a 385-405
day calving interval. In order to attain this objective, cows must get pregnant. As simple as it may sound, you must detect heats
and get cows inseminated in a timely manner. This is often much easier said than done.
The pregnancy rate (PR) is one parameter used to evaluate the reproductive performance in your herd. It is defined as the probability
of an open cow to become pregnant over a period of 21 days. The PR depends on two things:
-
Heat detection rate (HDR). This is the probability that a cow is seen in heat or inseminated over a period of 21 days, following
the voluntary period. The frequency at which cows are bred (insemination rate) is also a reflection of the heat detection rate in a herd.
-
Conception rate (CR) or breeding success.
The pregnancy rate is calculated with the following equation PR = HDR x CR.
This equation shows us that in order to get cows pregnant and obtain an acceptable calving interval, cows must be fertile, and most
of all, we must detect heats and inseminate them! Conception rates are difficult to change since it depends on multiple factors
(genetics, feeding, uterine health, infectious agents etc.). The most efficient way to increase the pregnancy rate is to improve
your heat detection rate and/or your insemination rate. The average PR in Ontario and Quebec is approximately 14%.
What is the level of heat detection in your herd? If you have a computerized preventative health data system with reproductive data
properly entered, this number is readily available. If not, you can make the calculation yourself. Over the course of the next 21 days,
write down the cows seen in heat that are eligible to be bred. This means cows in heat that are past the voluntary waiting period and
those who are in heat 18-24 days after their last breeding. Ideally all cows that are eligible should be bred. You can calculate the
HDR by dividing the total number of cows who were bred during the 21 days, by the number of cows who should have been bred. A HDR of
50% is considered excellent.
If your HDR is below 30%, changes need to be made to improve heat detection in your herd. Is heat detection a problem because other
farm tasks limit the amount of time you can spend detecting heats or you're just not seeing heats? If time is an issue, systematic
synchronization programs may help. Success of synchronization programs depends on: clearly identifying cows that need to be injected,
excellent record keeping, and management of injections (respect the dosage and storage of hormones, and strict adherence to timing of
the protocol). If you are not seeing heats, talk with your veterinarian about the signs you should look for or about other possibilities
that may limit the signs of heat (negative energy balance, cow comfort, etc.). One aspect that is often overlooked is bred cows must be
observed for heat until they are confirmed pregnant. You must identify and rapidly re-inseminate open cows. Regular visits by your vet
will identify these open cows. Your vet may recommend various strategies to get the cow bred as soon as possible.
Heat detection is very important for reproductive success on your farm. Take time to evaluate the heat detection rate with your
veterinarian and/or farm adviser.
|
