Every beef calf born is money in your client’s pocket, but getting consistently high conception, pregnancy and calving rates involves a lot of strategies even before cow meets bull. What can be done to improve fertility in a herd? Quite a few things, but it requires a commitment to management and long-term planning.

Good nutrition is the cornerstone
Proper nutrition is first on most veterinarians’ fertility checklists. Adequate protein and energy levels are the most important considerations. But excesses can be as big a problem as deficiencies. High levels of protein, for example, can cause problems with reproduction. “Alfalfa hay, especially if feeding to intake, may cause a problem because of excess nitrogen,” says Rick Funston, PhD, a reproductive physiologist at the University of Nebraska West Central Research and Extension Center.


Larry Horstman, DVM, MS, says heifers with a reproductive-tract score of 4 or 5 will respond to a heat synch program and milk better.

A mineral mix is also part of the equation. “There’s been a lot of work done on particular minerals and reproduction,” Funston says. “A lot of deficiencies become compounded: you can have adequate levels of copper but excess iron, molybdenum or sulfur – then the animal overall will be deficient in copper because these other minerals will decrease its availability.”


Zane Leininger, DVM, says dewormed cows, even in dry areas of the country, winter better.

Nutritional considerations should also include water quality. “There are a lot of sulfates in the water in southeastern Colorado, which ties up copper,” says Zane Leininger, DVM, Colorado Veterinary Clinic, La Junta, Colo. “Most of the country needs phosphorous, especially during the winter.”

For Lowell Rogers, DVM, Pine Belt Veterinary Hospital, Hattiesburg, Miss., phosphorous, while very low in the soil, is not a problem because of the use of high-phosphorous chicken litter. “Primarily, in my area, it’s just getting adequate protein and energy at the right time,” he says. “We’re not so much concerned about any one trace nutrient. There’s a lot of concern in the dairy industry about too high a protein level causing a buildup of ammonia in the uterus and decrease in fertility. There’s a lot of work on that, particularly related to ryegrass. I think we’ve proved it’s not as much a concern for the beef situation.”


Rick Funston, PhD, says body-condition score is even more important for heifers than cows.

In the Midwest, insufficient energy is a nutrition-related fertility problem, says Purdue University’s Larry Horstman, DVM, MS. “We also have a lot of fescue, which raises body temperature 2.5 degrees higher than an animal not grazing fescue and decreases fertility.


Lowell Rogers, DVM, believe BVDV is to blame for some reproductive problems he’s seen in herds.

“There’s good research that chlorotetracyline in the mineral mix can increase fertility in heifers and cows when fed 30 days prior to the breeding season and throughout,” Horstman adds. “Also, feeding whole soybeans increases the condition score of cows in this part of the country. We have people who start feeding it prior to the calving season. Calves have more vigor, and cows are in better condition and get bred back quicker.” He recommends feeding 3 pounds of whole soybeans daily.

Craig Iwanski, DVM, Central Veterinary Services, Stockton, Kan., points out that nutrition is critical all year round. “Eighty days postpartum makes the difference in breedback. How you feed in March and April makes a difference in how they breed in May and June.” Because the body takes care of maintenance first, reproduction will be the first thing to suffer if nutrition is inadequate.

Those effects are cumulative, too. “People get by on things that work in good years; they can get over a lot of problems,” Leininger notes. “But in a bad or average year, if cow condition is slipping, the wreck may come a year or two later. It may have been building up for a while.”


Because the body takes care of maintenance first, reproduction will be the first thing to suffer if nutrition is inadequate.

Parasite control might also fall in the nutrition category. More people are deworming since the price of the products has come down. I’m convinced that even in this dry county, it’s worthwhile,” Leininger says. “Ten or 15 years ago, I might have said it’s not economical. I’ve changed my mind. Dewormed cows winter better.”

Maintain body-condition score
Body-condition score is the best indicator of how the nutritional program is working. “Cows should be calving at a body-condition score of 5,” Iwanski says. “At pre-breeding, they should be at least 5 or more.” Body-condition score is even more important for heifers than cows because they are still growing themselves, in addition to the work of nursing and getting rebred. Heifers should score from 5.5 to 6.

There’s little advantage in being over a 6, Funston says, but being too high is a rare problem. Being too low is more common and more dangerous. “If it’s too low at calving, it’s difficult to gain weight,” Funston says. “If you increase the diet or energy level, you just increase milk production.”

“The biggest thing I’ve learned is that body-condition score at calving is the most important thing,” Rogers says. “No matter how you feed them after calving, you won’t decrease postpartum anestrous if their score was below 5 at calving.”

Bovine viral diarrhea virus vaccinations should be on the list of vaccinations as the disease has reproductive ramifications. Rogers thinks that is what he’s been seeing in some herds. “In the past four years, we have seen a much higher rate of abortion in 90 percent of the herds I deal with. We’ve always encouraged vaccinating heifers with modified-live BVDV before breeding, but two years ago we began pushing the vaccinating of mature cows, while they are open, with a modified-live BVDV vaccine. For a strung-out breeding season, you might have to go into the herd twice or more to get the whole herd done, but the next year you can vaccinate while pregnant if you use the right MLV product.”

Horstman notes that the vaccination checklist should include leptospirosis, specifically for serovar Hardjo-bovis. “We’ve used it in a few herds, and it has helped.” Rogers says it will be a big boost to fertility in his area, where levels of Hardjo-bovis are high.

Iwanski also recommends Bangs vaccinating virgin heifers and adding IBR, BVD, PI3 and BRSV to the list, as well as a Neospora vaccine in some areas.

Avoid dystocia
Early assistance has been shown to positively affect the postpartum interval. Herds where dams were given early assistance also had a higher percentage in heat by the beginning of the breeding season, a trend toward fewer services per conception, an increase in fall pregnancy rate and heavier calves at weaning.

Calving assistance can be too early – stage II of parturition should have begun before assistance is given. However, providing assistance quickly when it’s needed can benefit the calf, too, as calf survival at weaning is higher.

Measure heifers
Heifer pelvic measurements and reproductive tract scores should be taken before they go into synch or breeding programs, Iwanski says. “The pelvis grows a quarter of a centimeter squared every day. If they measure 140 square centimeters at 10 or 11 months old, divide that by 2 to get 70 square centimeters. That means she should be able to have a 70-pound calf unassisted,” Iwanski says. At 12 to 13 months old and 500 to 700 pounds, 145 square centimeters is about the minimum you want to see.

“We do reproductive tract scores in heifers a month before breeding, evaluating the reproductive tract for sexual maturity,” Horstman says. “We give them a score from 1, meaning very immature, to 5, meaning the uterus has good size and tone and structures on the ovary indicating that they are cycling. We want them at 4 or 5 so they will respond to a heat synch program, milk better and calve earlier in the season.”

Direct reproductive traits, as we are able to measure them today, are lowly heritable – on the order of 10 percent or less. “Genetic selection of lowly heritable traits is an inefficient process,” says Funston. “But lowly heritable traits respond most favorably to crossbreeding.”

Synchronization programs
Some veterinarians see advantages to synchronization programs. “The uniformity of the herd will improve, especially with CIDR implants, GnRH and prostoglandin,” Iwanski says. “Non-cyclers will cycle and conceive, and the postpartum interval will be shortened.” It will mean extra work, because everything else has to be stepped up – better nutritional programs, extra management and extra care. “You’re asking her to do something extra, earlier.” In one herd, Iwanski has been able to decrease the calving interval by 22 days with synchronization.

Using CIDRs can help prevent the short cycling that occurs after calving; it can also help match up late calvers or at-risk animals – 2- or 3-year-olds in less than optimal body-condition score.

On the other hand, since they’ve got to be cycling for synchronization to work best, “you leave those early calvers without a bull for several cycles, and you can miss a good heat,” Rogers says. “You can get calves in a shorter period, but not earlier. In fact, later, because you’ve got to let some heats go by.”

The main advantages of synchronization programs are decreasing the amount of time spent in heat detection and grouping the calving season, but they are not fertility drugs, Horstman says. “You can jump-start some cows not cycling in the breeding season with the use of CIDRs. But if we have a group we have to jump-start, there’s something wrong with the system.”

Other techniques

  • Practice horn breeding. “When using AI, there’s some evidence if you put semen in the horn on the side the cow will ovulate from, there is a better chance of conception,” Horstman says.
  • Use a sheath protector. “There are a few diseases that can cause vaginitis,” Horstman says. Ureaplasma and mycoplasma are just a couple of them. “When breeding infected cows, you can carry infection into the uterus.” Using sheath protectors when artificially inseminating will help decrease the chances of carrying infection into the uterus.
  • Feed ionophores. Aside from the advertised benefits of ionophores, there’s some indication that they may have a positive effect on signaling reproductive hormones to be released, says Funston. Scientists have also demonstrated that heifers fed an ionophore reach puberty at an earlier age and a lighter weight.
  • Cull less-fertile animals. Following a 60-day cow- and a 45-day-heifer-breeding season, cull open animals. “You’ll be selecting for more fertile animals,” Horstman says. “You can increase the innate fertility of the herd.”
  • Castrate bull calves early. It’s been shown that bull calves suckle more aggressively than steers and heifers. Cows nursing bulls will cycle later than cows nursing heifers or steers.
  • Wean calves early. “There’s good forage in October and November that will allow cows to gain weight without supplementation, instead of losing weight with a calf,” Leininger says. “It could make the difference of a body-condition score at least.” In his area of Colorado, it’s almost impossible, economically, to have a cow gain weight in winter.
  • Consider the environment. Animals that are too large or milk too much for the resources available will start to drop off in reproductive performance. The breeding season also needs to be matched to the environment. “If you’re trying to breed animals when it’s hot, you may need to change the breeding season,” Horstman says. In the heat, sperm quality goes down, and cows may not show heat as well. 

Heifer fertility


First-calf heifers often get all the attention, but you might want to keep an eye on second-calf heifers.

Breeding virgin heifers is generally not difficult if they are maintained at target weight. “The problem is the first-calf heifer, even the second-calf heifer,” says Rick Funston, PhD. “Part of that is a management issue. First-calf heifers are often managed separately. For the second-timer, they get lost in the cow herd. But the fallout with the third pregnancy may be even greater than for the second. Maybe we need to look at managing two- and three-year-olds together.”

Breeding heifers ahead of the cow herd is pretty common practice. In North Platte, Neb., Funston says they’ve been looking at that practice and breeding heifers either with cows or before. Over three sets of heifers, no difference was seen. “That was with summer-born calves – of course the heifers bred to calve earlier had heavier calves in the fall because they were older,” Funston says. “But the nutrients in June and later are declining; the nutrients available are less than for those born a month early.” Pregnancy rate with a second calf was not different, but with those bred in August and September, rebreeding was 10 percent lower than for spring heifers.

A Journal of Animal Science article (in press) describes a study of spring heifers weighing 53 percent and 58 percent of their mature weight at breeding, which was conducted to determine the effects of developing heifers to a lower weight at breeding than traditionally recommended. There was no difference in reproductive rate, calving difficulty or calf performance through the third gestation. Reproductive performance was acceptable at both target weights.

“Both of these systems were looking at ways to decrease heifer development cost, by breeding at a lighter weight or breeding with the cow herd, so you don’t have to have a high plane of nutrition to reach the same weight a month earlier,” Funston says.

Bull checklist

A bull’s checklist includes many of the same things as his female counterpart’s.

  • Provide good nutrition, including a good mineral mix, the same as the cow herd.
  • Have a body-condition score of 5 to 7. “I always say a bull should be able to lose 200 pounds and still be in good shape,” says Craig Iwanski, DVM.
  • Perform a breeding soundness exam at the beginning of every season. “People say, ‘I know he’s good because I have calves on the ground.’ That means he was good last year,” says Lowell Rogers, DVM. “All bulls will go bad sooner or later.” The yearly exam is also a chance to make sure his penis is uninjured and functioning properly, adds Zane Leininger, DVM. The exam could be the most important determinant of the fertility of a herd.
  • Select for large scrotal circumference. “Bulls with a large scrotal circumference have daughters that reach maturity quicker and are more fertile and productive throughout their life,” Larry Horstman, DVM, says. The minimum standard, for a yearling, is generally said to be 32 centimeters. “I’d rather see at least 38 centimeters. For every centimeter increase, their daughters reach maturity that much quicker.”
  • Check legs and trim feet as necessary.
  • Deworm and control flies.
  • Control disease. Bulls need the same vaccinations as the cows. Also, trichomoniasis can be a bigger problem, especially with older bulls. “The vaccine for leptospirosis Hardjo-bovis is also important for bulls,” Rogers says. “Just be aware that the titer gets so high you might not be able to collect semen or export him.”   
  • Check him for the Fertility Associated Antigen. “Some bulls have this factor in their semen, and they settle more cows,” Horstman says. “There are chuteside tests available to see if they have it. University of Arizona research has shown that the bulls that have it are 9-40 percent more fertile.”
  • Try to manage young bulls separately. “We know if we put heifers together with cows, we’ll have a wreck,” Leininger says. “But, we’ll dump yearling bulls in with the bull herd and not think anything about it. A young bull needs a little extra care and attention while he grows up.”