From fetus to calf, yearling, first-calf heifer and mature cow, every age female on the cow-calf operation needs attention to create reproductive momentum.
From fetus to calf, yearling, first-calf heifer and mature cow, every age female on the cow-calf operation needs attention to create reproductive momentum.

Bob Larson, DVM, PhD, Dipl. ACT, Dipl. ACVPM, Kansas State University, believes heifer development is critically important and is one of the most important things veterinarians can do for their beef cattle clients.

“I think it’s a classic win-win situation,” Larson says. “It makes money for the veterinary practice, it’s rewarding, it taps into a lot of things we are good at in veterinary medicine and it is really beneficial to our clients. I think heifer developing is one of the most important economic management things that you are going to do on a farm or ranch.”

Creating beef reproductive momentumOne of the most critical ways you can create what Larson calls “reproductive momentum” is to look at all ages of female cattle on the operation at each stage of their development and reproductive life cycle. This can help you and your clients coordinate everything from breeding to calving on-time and on-schedule for the following years. Larson says the goal of creating momentum is to get cows and heifers bred early, calving on time and re-bred to calve on time the following years. This momentum will help your clients reduce time lags and days open in the cowherd. “I have to have momentum working for me,” he says. “To use an analogy from driving: I can’t ever take my foot off the gas. I am not running real fast, but I’m running steady.”

Start with the cows
For spring-calving herds in the pre-calving winter months, Larson suggests looking at each group separately. “There is more than one group of females on a farm at any given time,” Larson says. Different groups include the mature cows, first-calf heifers, yearlings, baby calves and those in utero.

One group to focus on are the mature pregnant cows that will be calving soon. Cows need to calve in good body condition, and Larson recommends aiming for almost all of the mature cows in the herd to have a BCS of about 5. “If  cows are thin, producers need to provide a supplement to the base forage,” he says. “In general, supplementing thin cows on moderate to poor-quality forage can be different than supplementing moderate-condition cows. With low-protein forage, supplementing protein will increase intake – this is often all that is needed to maintain moderate condition cows on low-quality forage.”

For thin cows on low-quality forage, they will probably need additional energy in the form of grain or grain by-products. “Grain byproducts will likely provide sufficient protein to improve ration quality, but grains will likely need supplemental protein when fed to cows on low-quality forages.”

Extremely thin cows can fail to survive until spring particularly if challenged by severe winter weather. “Most thin cows will survive, but are at higher risk for dystocia and delayed breed-back,” Larson says. “Thin cows at calving are at high risk of failing to become pregnant in the subsequent breeding season.” Conversely, too-fat cows can have abdominal fat deposit in the pelvic canal and dystocia becomes more likely.

Cows that are not lactating have lower mineral requirement than lactating cows, Larson says. “However, if cows are consuming dormant forage or poor-quality hay, intake will be low and this affects not only energy and protein intake, but mineral intake as well. Salt is always the most important mineral to provide cows, and depending on what feeds are being used to supplement forage, a good-quality mineral mix may be helpful.”

In many parts of the country, cows are not likely to be picking up internal parasites during the winter months, but depending on your location and parasite burden, deworming should also be considered at this time.

Two-year -old heifers
Making sure that heifers calving for the first time are in adequate body condition (closer to a BCS 6 for calf heifers) is even more important than it is for mature cows, because the length of time to resume fertile cycles after calving is longer in first-calf heifers than mature cows.          

While the 82-day difference (see sidebar) between the length of gestation (283 days) and the length of a year (365 days) provides a moderate challenge for mature cows, this difference is a significant problem for first calf heifers. “Most first-calf heifers require 80 to 100 days after calving to resume fertile cycles if they are in good body condition,” Larson says. “This obviously makes it difficult to have a high percentage of heifers nursing their first calves to become pregnant early enough in the breeding season to calve by the same date for their second calf as they did for their first calf. And, thin heifers require even a longer period of time to resume fertile cycles after calving.”

First-calf heifers are at greater risk of becoming thin while consuming poor-quality forages than mature cows because these younger females still require nutrients for their own growth as well as for weight maintenance and fetal growth. “First calf heifers are adding bodyweight as muscle and bone, therefore, they are going to need to gain about one pound per day during their first gestation,” Larson says. “The last part of gestation, you are going to get another 150-180 lbs of conceptus growth, this includes the calf, the fluids, and the placenta. The conceptus weight gain is in addition to the bodyweight gain of first-calf heifers from the time they are bred until the time they calve.”

You can’t let them get thin in late gestation, Larson says. “I can’t make that up once they start lactating, and I am going to have too long of a postpartum anestrous if they calve thin. If they calve in good body condition I need to make sure they stay there after calving.”

Because of the greater nutrient requirements for growing pregnant heifers compared to mature pregnant cows, and because of the social interactions that tend to relegate younger, smaller, two-year-old heifers to a subservient status in the herd, Larson does not recommend providing supplement to mature cows and two-year-old heifers in the same pen or pasture.

Separating first-calf heifers from mature cows removes most of the negative social behavior that leads to reduced intake by the younger, smaller cattle in the feeding group.

As with the cows, depending on location and parasite burden, deworming should also be considered at this time.

Yearling heifers
When your clients are busy with pre-calving and calving cows and heifers, the yearlings often get forgotten, but they’ll be next year’s new calving heifers and still need attention. Yearlings are approaching puberty and should be approaching their target body weight, which is generally 55-60% of their mature body weight for most breeds and 65% of mature weight for Bos indicus (Brahman)-cross cows.

Yearling heifers need to be on a good plane of nutrition to meet their growth needs. “Because mature cows will maintain body weight on moderate-quality forage, some ranchers forget that growing yearling heifers will not gain the weight they need to reach puberty on the same quality of forage,” Larson says. “Depending on the timing of the breeding season relative to forage quality and quantity, it is unlikely that heifers that grew slowly during the winter months will be able to gain enough weight on lush growing forage to reach puberty in time for the start of the breeding season.”

Creating beef reproductive momentumLarson explains that the onset of puberty is primarily influenced by age and weight, so heifers need to be gaining sufficient weight to attain puberty before the start of the breeding season.

In much of the U.S., forage availability in the winter is limited to standing dormant forage or baled forage. Only high-quality forage provides the nutrient density necessary to meet the gain requirements to reach the weights associated with the onset of puberty. “If forage quality at this time of year is moderate to poor, yearling heifers are not likely to achieve the weight gain needed to reach puberty prior to the onset of breeding without supplementation,” Larson says. “Supplementing yearling heifers is required to meet weight gain goals in most forage situations.”

For this age heifer, weight is a better indicator than body condition score as to their development. “Body condition score is a great tool to estimate energy reserves in mature cattle but it provides less information in growing animals,” Larson says. “I prefer to use weight and weight gain in growing heifers as an indication of nutritional status. Even so, if weighing heifers is not possible, a BCS of about 6 is a good target for heifers approaching puberty.”

Delayed onset of puberty due to slower growth and weight gain means putting the brakes on future reproductive momentum. “Heifers that have not reached puberty at the start of the breeding season are much less likely to become pregnant during the breeding season,” Larson says. “And if they do become pregnant, it is likely to be late in the breeding season – leading to a late calving and a significant risk of failing to become pregnant the following year.”

Larson adds that depending on the timing of the breeding season, some veterinarians will recommend vaccinating yearling against abortion-causing pathogens during mid-winter.

Calves on the ground and in utero
And you can’t forget the littlest, future member of your client’s herd – the heifer calf on the ground and the developing fetus preparing to be born. Larson says a number of researchers are pointing to evidence that protein and energy deficiencies during gestation can have negative effects on the fetus that extend well beyond parturition and the first few weeks of life. There is also evidence that nutrition during gestation impacts the quantity and quality of colostrums available for calves.

“To ensure good consumption of colostrum and adequate passive transfer, both the cow and calf need to stand shortly after parturition and the calf needs to have an aggressive suck reflex,” Larson says. “Cows that calve in thin body condition are more likely to have a prolonged birth and are at greater risk for dystocia, causing either the cow or the calf (or both) to not stand and initiate suckling/nursing shortly after parturition.

Maintaining adequate body condition during gestation has benefits for the cow, the fetus, and the rancher, Larson says.

“If you can get the scenario of positive momentum going and then protect it, it will be a self-fulfilling, positive feedback loop to make it easier to have a successful breeding season next year.”



Body condition and momentum
How does body condition influence reproductive momentum and breed back?

Bob Larson, DVM, PhD, Dipl. ACT, Dipl. ACVPM, says because a year is 365 days and cow gestation is about 283 days, cows must rebreed within 82 days after calving to calve at the same time or earlier the following year.

“I expect most cows in moderate body condition (BCS 5) to be cycling sooner than 82 days after calving, but thin cows can require an extra 10 days, 20 days, 40 days or more to resume fertile cycles after calving,” he explains. “This delay allows cows to either fail to become pregnant or become pregnant later in the breeding season – which works against the momentum we want to develop that results in almost all cows having fertile cycles before the start of the breeding season, a high percentage becoming pregnant in the first 21 days of the breeding season and a high over-all pregnancy percentage to a controlled breeding season.”


Get on the farm
Creating beef reproductive momentumVeterinarians can be key to helping beef clients maintain a successful reproductive program, and the best way to do that is to get on the farm, says Bob Larson, DVM, PhD, Dipl. ACT, Dipl. ACVPM.

 “I think it’s very important to get on the farm to evaluate heifers at least once between weaning and the time for a pre-breeding exam,” Larson suggests. “If it’s a large group of heifers, you don’t have to run them all through the chute, but get a bodyweight on some of them and put your hands on some of them, so that you can evaluate how the group is growing. If their target weights are not being met you can adjust the ration and get that group where it needs to go.

“If we don’t measure, interpret, look at, palpate these heifers, we are letting Mother Nature take her course and it’s a 50:50 deal if they are cycling when we need them to,” Larson adds.

 Get on the farm one more time per year than you used to, Larson suggests. “Get on the farm two more times in the year than you used to. Let’s figure out some ways to get on the farm that result in win-win situations for the veterinarian and producer.”

 A good time to get on the farm is in mid-gestation when there are pregnant replacement heifers. “To have a good calving season and a short post-partum interval at this time she has got to be in a great body condition. At mid-gestation is a great time to get out there and determine body condition, weigh them, see where these heifers are condition-wise. I also want to check on my mature cows as well. I have to assure that body condition going into calving is good because I don’t have a lot to days between calving and breeding to work with.”

If the veterinarian is involved every year, the heifers can successfully calve and rebreed every year because you make modifications if necessary, he says. “It’s why I preach heifer development. Without veterinary involvement, it works some years and some years it doesn’t. With us, producers can make it work every year.”