There is a common myth regarding bovine pregnancy that says that cows can get pregnant at any given time, which is untrue. Getting cows pregnant is not as easy as walking a cow to the cattle trough, for instance, and farmers have extensive knowledge on how and when such a thing is possible. Their knowledge is broken down, as follows.
What are heifers?
Heifer is the name given to a female cow which is six months old or older and has not yet given birth to a calf. Female cows reach their puberty between 8 and 16 months of age, and it is during this period that they may get pregnant for the first time. Factors such as breed and size play a significant role in the development of female cows.
The preferred age for the first pregnancy of a cow is 15 months so that it can deliver its first calf around the time when it becomes two years old. Sometimes, cows can get pregnant earlier, and that can result in better productivity for them over their lifespan.
Puberty can be let to happen naturally, but farmers can feed the heifers more so that they gain enough weight to be able to sustain a pregnancy.
What is the estrous cycle in cows and how does it happen?
Cows, like all mammals, have something called an estrous cycle. This cycle happens for an 18 to 24 day period, and the goal of any farmer raising cattle is to synchronize the estrus in the cows that must be bred.
The use of hormonal implants is widespread for this particular purpose. The hormones used should not be mistaken for BST or bovine somatotropin, as the latter is used to get cows to deliver more milk, and it is mainly used in the US, as in Europe and other countries, it is banned.
Only when cows reach the heat stage of their estrous cycle, they can be mated. During the rest of the time, they will not allow a bull to mount them, and, in case artificial insemination is practiced, the ovum will not be available for fecundation.
How do farmers know when cows are in heat?
Cows in heat have specific behavioral symptoms that will let farmers right away that they are receptive to mating. They will manifest through increased agitation, compulsive sniffing of themselves and other cows, and they may even attempt to mount other cows in the herd.
In case the other cows do not move away when this happens, that is usually a sign that they are also in heat. So, in a way, a cow that becomes more active due to its heat can single out other cows in the same stage of their estrous cycle.
How does mating happen?
Cows in heat can remain pregnant, and that can happen naturally by being mated with a bull, or through artificial insemination. The latter practice is quite common, especially for dairy cows, as farmers prefer the ease of use, and the ability to pick semen from different bulls so that the stock of calves will not come from the same sire.
Not all herds have bulls, and there can be a shortage of available sires in the area, all being factors that contribute to the popularity of artificial insemination. However, what must be kept in mind is that cows still need to be in heat even if this method is used, as otherwise, a viable ovum would not be available.
Monitoring the cows is essential so that farmers know when they go in heat. Different methods can be used. For instance, farmers paint their cows’ tail with a visible color and, if they notice that the paint wore off, that is a sign that another cow tried to mount them.
Other methods include the use of a pedometer that will signal when a cow becomes more agitated, or of a detector called a Kamar pad that will turn red when a cow is mounted.
Several factors play an essential role in successful mating and pregnancy. For instance, the heifer must be in good overall condition, as being underweight may cause troubles for both the cow and its calf. That doesn’t mean, however, that cows should be overfed. When overweight, they might experience problems with their pregnancies, as well.
The breed of the bull used for mating, or from which the semen is collected for artificial insemination, also matters. Getting a cow pregnant with sperm from a bull that is from a breed considerably larger in size can result in calves that are too large to go through a cow’s pelvis. If that happens, a cesarean section must be performed on the pregnant cow.
Extra precautions for heifers
The average duration of pregnancy for cows is 283 days. For heifers, more attention is needed, as they go through their first pregnancy. Cows continue to grow until they reach three years old, and that’s why heifers need to have adequate nutrition so that their pregnancy doesn’t make them too weak or stops their natural development.
How fast can cows get pregnant again?
Most cattle farms aim at one calf per year for every cow that can be bred. That means that within three months after calving, a cow should become pregnant again. Artificial insemination is extensively used for this purpose. However, it must be noted that not all the attempts are successful, and mostly, cows can get pregnant every 400 days or more.
For milking purposes, calves are separated from their mothers within just a few days from birth. However, to allow the calves to grow, even after being separated from their mothers, the first milk from the cows, called colostrum, must be fed only to their young.
A cow that gave birth will continue to provide milk for about ten months after calving, and after that, it will go through a dry period. Farmers try to make this period coincide with the dry period necessary for cows that are already seven months pregnant so that a complete cycle can be met.