Cow Fertility – How Old Do Cows Have to Be To Reproduce?
The age of a female bovine affects her fertility in several ways: genetically, environmentally, nutritionally and even physiologically. For the purpose of this article, a “cow” will not be used colloquially because I wish to avoid confusion between what the general term of cow is and the true meaning of “cow”. As such, I suggest that you do best to ignore the colloquailism in the title of this article. By definition, a cow, is specifically a mature female bovine that has given birth to and/or raised at least one or two calves. A heifer, though, is an immature female bovine that has never given birth to a calf. This article will primarily discuss the age when heifers first show signs of “heat” or estrus and thus are ready to breed. However, it will also discuss the fertility and breeding range of a mature cow, both beef and dairy and what affects a cow’s fertility and longevity in the cow-herd..
A heifer generally should be ready to breed at around 15 months of age. Note that I said generally because even this age is varied depending on breed/genetics, nutritional level, body condition, and management factors. Majority of the time, though a heifer is ready to breed based on weight, not age. Therefore a heifer should be at least 60% of her mature body weight or of the average mature cowherd’s weight when ready breed. The best explanation for this is due to the heifer’s size and physical conformation. By even 15 months of age a heifer still may be too small to be ready to be bred, not to mention her pelvic size or overall conformation is inadequate for her to even give birth to a calf. Such conformational inadequacies may prove to be a problem by the time it is time for her to give birth; dystocia or birthing problems may result and the produce most likely will have to assist in either pulling the calf out, or have the vet come out to perform a caesarean section on her to get the calf out as quickly as possible.
It is ironic to note, however, that some heifers can be bred at a lighter weight and younger age than what the guidelines above suggest. I have heard several stories of such a thing happening, and a number of those anecdotes mention that the producer didn’t even know a certain heifer was pregnant until there was a calf on the ground and she was suckling that calf. The heifer may have just been weaned and already been bred, either by one the bull calves in the herd with her, or the one of the herd bulls themselves. This comes to little surprise to me considering how much the fertility of cattle have increased over the years, from the mid-1800s to today. During that time period, a steer was deemed fit to butcher when he was about three to four years of age. A heifer was ready to breed about that age as well. Fast forward a couple hundred years and heifers have decreased in the age at which they reach sexual maturity considerably.
With more focus on important production factors such as cow fertility in order to decrease overhead costs, I am finding more stories on heifers reaching puberty and being ready to be bred much sooner and at lighter weights than what is expected of them. Interestingly, some producers have taken advantage of this in order to reduce feed costs. From the time a heifer is typically weaned, which is at around 6 months of age, it takes around 9 to 10 months of feeding before a group of heifers are deemed ready to be impregnated via natural service or artificial insemination. Since more heifers can be ready to breed as early as 9 to 12 months of age, this can reduce the feeding period of these replacement heifers by a third to even half. In other words, instead of having a 10 month-long feeding period, you may end up having only a 3 to 6 month period. I must caution you, though, to not do this if you have a herd that is not highly fertile or of Brahma/Zebu breeding.
Most heifers of Brahman or Zebu breeding will, on average, may be ready to breed at around 20 to 24 months. Those of composite breeding, like Brangus or Beefmaster which are European-Brahman cross, often can be bred a little sooner such as at around 18 months of age. Some Brahman heifers may be pretty good at being able to be bred at this age as well, depending on their genetics. A herd not of Brahman or any sort of Bos indicus breeding may unfortunately have heifers not being able to be bred at this age too, which should be a marked concern because it is a sign of decreased fertility in your cowherd. (Another sign is cows being unable to get back to normal estrus cycling after giving birth to a calf.)
Various breeds have different rates of fertility and than others. For example, Jersey heifers can be ready to be bred at an earlier age than Charolais or Limousin heifers. Gelbvieh heifers can be seen to reach sexual maturity earlier and as a result be ready to breed earlier than either of the latter breeds or Simmental can be. It may be different Simmental-crossbred or fullblood heifers, as they quite possibly would be able to reach breeding age around the same time as Gelbvieh or even purebred Angus females might. However, note that there’s actually more variation within a breed than between breeds. Compare two Angus herds within the same location as each other: one herd may have heifers that have a lower breeding age than the other. Genetics and management criteria will have a big part to play here, because what one producer selects for in their herd isn’t always the same thing a different producer selects for in theirs.
The Optimum Reproduction Age for a Cow
Cows are liable to be productive throughout their lives, from the time they are no longer considered to be heifers to death. This means that they are already of reproductive age to produce a calf. The question now is their level of fertility. A cow’s fertility is actually more directly affected by the amount of fat she carries over her body, than genetics and is rated by a process called Body Condition Scoring. Heritability for fertility is very low to the point where some producers may consider it less significant compared to other, more heritable traits such as body weight and muscling ability. Body condition scoring is key to judge whether a cow–as well as a heifer–is too fat or too thin. Cows and heifers that are either too fat or too thin have lower fertility than those with normal condition. A cow of either of these extremes will take longer to come back into normal estrus cycling after she has given birth than if she were around normal condition. By the time breeding season ends she may be still open (not pregnant), or bred later than what is considered desirable for a cowherd.
Body condition scoring in heifers is just as important. A heifer that is too thin does not have enough muscle mass or energy to sustain a calf throughout gestation; she may have calving problems because of the very high amount of energy it takes to push out a calf for the very first time. If a producer suddenly ups the quality intake of a group of thin heifers during the third trimester he may see calving problems result because all that good-quality feed is being put into the late-term fetus, not the heifers. Thin heifers and cows also may not produce as much milk as is needed to feed a calf. This may be different in dairy heifers because they are selected for higher milk production than their beef counterparts. At the other extreme, a heifer that is too fat will also have trouble birthing because of the fat deposits in the birth canal will hinder the progress of the calf as it is pushed through. A fat heifer may experience reduced milk production because the fat deposits in the udder will reduce the amount of milk being produced. This is often a problem with show-heifers that are fed to look rounded and fat for the show-ring.
For good fertility in your herd, monitor nutrition levels in your replacement heifer and cow herd so that your females get the nutrition they need to maintain a health weight and a healthy body condition to be able to settle quickly. This must carry through during the time they are carrying a calf and to the time they are lactating. Heifers should be of more concern than the cows because of the fact that they are still growing and developing into mature cows.