The goal of pregnancy checking is not just to determine whether a cow is pregnant but also to determine why it’s not
Fertility is the most important trait in a cow herd. All other traits are negated if the female doesn’t get pregnant or fails to carry a pregnancy to term.
If the latter occurs, it’s important to find out why.
Duane Mickelsen, former university professor and cattle breeder near Pullman, Washington, has spent a lifetime specializing in reproductive problems in cattle, both private practice and while teaching bovine theriogenology and obstetrics to veterinary students. He was the first veterinarian to diagnose bovine trichomoniasis in Washington, Oregon and Montana in 1978 and he still does semen testing and pregnancy checking in several herds.
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Mickelsen said preg checking is not just to determine whether a cow is pregnant, but to also determine why it’s not. First calvers may have poor breed-back due to dystocia with their first calf, long recovery from calving or are slow to start cycling again due to inadequate nutrition while lactating and still growing.
“Inadequate nutrition can also delay puberty in heifers, reduce conception rates, decrease skeletal and muscle growth and increase the frequency of dystocia and failure to cycle again after calving,” he said.
“One study showed that with poor nutrition, follicles degenerate and the animal fails to come into heat. In one group we looked at, 87 percent of the heifers were not cycling due to lack of protein and energy in their diet. Sometimes it’s partly genetics if the heifers are big-framed, slow-maturing cattle, especially if they haven’t had adequate feed.”
Genetics play a role in feed efficiency, which also affects fertility. Easy-keeping cows tend to be more fertile.
Mickelsen also noted the importance of hybrid vigour. All else being equal, crossbred females tend to be more fertile and stay in the herd longer than their straightbred counterparts. But purebred breeders can also select for more fertile cattle.
Kit Pharo, a cattle breeder near Cheyenne Wells, Colorado, has for several decades selected seedstock that are more efficient and more fertile than the average.
He said producers who make a living from their cows know that fertility is by far the most important economic trait.
“Studies have shown that reproductive traits are twice as important as growth traits, which are twice as important as carcass traits,” says Pharo.
“Ironically, most folks in the beef industry have been selecting almost exclusively for growth and carcass traits the past 40 years, at the expense of reproduction. Academic folks have told us that heritability of fertility is so low we shouldn’t waste time selecting for it. If you were able to isolate fertility from everything else, that assumption might appear to be true. In the real world, however, nothing is isolated.
“Fertility is more a function of fleshing ability than of anything else, and fleshing ability is a function of low maintenance requirements. Reproduction cannot take place until maintenance requirements have been met and the cow is storing energy reserves (fat). Since fleshing ability and maintenance requirements are very heritable, fertility is also very heritable,” Pharo said.
As the beef industry selected for more growth and less back fat, producers inadvertently selected for lower fertility.
“This created late-maturing, hard-keeping, high-maintenance cows that struggle to reproduce under traditional ranch conditions.”
To maintain those cows and have them rebreed, ranchers had to increase supplemental feeding. Instead of producing cows to fit their environment, they supplied expensive inputs to fit their cows’ needs.
Steve Hendrick of the Coaldale Veterinary Clinic in Coaldale, Alta., said fertility is extremely important to profitability.
“Nutrition is important, but you also want to start out with a fertile type of cow. It’s interesting to hear people discuss the question of proper age and size of heifers at breeding as the two most determining factors on pregnancy rates.
“I agree with age as a criteria, but size is a tricky topic. All too often, producers choose the bigger animals, but those may be slower to mature.”
The average cows in most breeds are much larger than they used to be.
“This makes it hard to judge a heifer and determine whether she will mature to be 1,300 pounds or 1,500 lb. When estimating whether a heifer is between 55 to 65 percent of her mature body weight at breeding time, you don’t really know. You could look at the dam and maybe have an idea based on her size, but that’s only half the equation. We don’t always know what genes for size the heifer got from her sire,” said Hendrick.
Frame score charts can help estimate mature frame size, if age, weight and hip height of the heifer are known.
“These might help you guess what her mature size and body weight might be, at least in terms of whether she will be a large frame or smaller frame,” says Hendrick.
“It’s also important to put selection pressure on replacement heifers, and only give them a short breeding season, just one or two cycles. The ones that don’t breed early are not as fertile.”
Inherent fertility is important but other factors come into play.
“If cows or heifers are too thin, they won’t breed. Here in Canada, we use the five-point body condition scale, so we say that any female that is less than 2.5 on that scale is less likely to breed. There is higher risk for cows not cycling when they are thin,” Hendrick said.
Reproductive diseases can also cause infertility. Dr. Eduardo Cobo at the University of Calgary said trichomoniasis and campylobacteriosis (vibriosis) are two of the main reproductive diseases that reduce pregnancy rates. These sexually transmitted diseases are often under-diagnosed.
“If a herd has fertility problems and uses natural service for breeding, producers should not ignore the possibility that they have one or both of these diseases,” he said.
“Both of these diseases kill the embryo or fetus, mostly in the first months of gestation. The cow is bred and becomes pregnant, but the pregnancy doesn’t last long. It’s often an early embryo mortality rather than an abortion; you don’t see the fetus.
“This is different than most of the other reproductive diseases like brucellosis, leptospirosis, IBR or BVD. When those diseases kill the fetus, it might be several months old and you see the abortion,” Cobo said.
