The traditional approach for heifer development has been to shoot for 65% of mature body weight at breeding time in order to maximize pregnancy rate. Is maximum pregnancy rate really the goal, or is a more profitable herd the goal?
Studies by Rick Funston of the University of Nebraska and others have investigated that question. Most results indicate that we can develop heifers to 51%-58% of mature body weight and achieve very acceptable pregnancy rates.
If your average cow weighs 1,390 lbs. (and many do), a heifer would need to weigh 904 lbs. at breeding in a traditional system, but only 709-806 lbs., according to the recent research. However, I’d caution readers that if the average weight of your heifers is 709 lbs. at breeding, many heifers could be below that 709-lb. threshold.
Having all heifers at or above the target of 709 lbs. is the goal. However, if your heifers traditionally weigh 900 lbs. or more at breeding, I would suggest developing heifers to about 800 lbs. before you go lower. If acceptable rates are achieved, then a further reduction would be warranted. Remember, the goal isn’t to get the most heifers pregnant, but to optimize profit.
Many areas of the country have abundant feed resources, so it’s easily possible to have heifers weighing 900 lbs. or more at 14-15 months of age. If a heifer weighs 500 lbs. at 200 days of age and the target is 800 lbs., we only need a gain of 300 lbs. in 235 days, or 1.3 lbs./day.
The gain from weaning to breeding doesn’t have to be steady. We background our potential replacement heifers for 30 days post-weaning and then graze them on cornstalk residue or stockpiled pasture for 60 days. We’ll supplement some protein if needed, but this low-quality forage, along with free-choice salt-mineral mix, is often all they need.
This is the key to cost-effective heifer development. We’ve found that most heifers do fine on this diet, while a few lose weight. If this latter group can’t thrive on low-quality forage as heifers, we’re concerned about their longevity as cows with months of low-quality forage to graze.
Other benefits to the lower breeding weight target for heifers are their improved efficiency during the winter feeding period, as well as increased gains in the subsequent grazing season. If our heifers now weigh 500-525 lbs. after 60 days of winter grazing, they must gain 275-300 lbs., or 1.6-1.7 lbs./day, which is easily achievable on a low-cost ration.
Other keys to successful heifer development with an acceptable pregnancy rate (80%-90%) are to keep back more heifers than needed to produce enough pregnant females, and to use a shortened breeding season (45 days) vs. the 65-day season for mature cows. I advocate a 45-day breeding season for heifers, because in a 65-day season with a traditionally developed heifer, a late-calving (after 45 days) heifer is much more likely to be open the following season.
One of the real keys to getting heifers bred is to have them gaining weight at time of breeding. Excellent studies from Purdue University and the University of Wyoming indicate poor conception rates when heifers are well-developed up until breeding and then turned out on grass, where they lose weight.
Pregnancy is a luxury to the cow’s system. If her nutrition is limiting, the cow shifts her priority to survival, at the expense of the fetus.
Develop a heifer that will be gaining weight as she goes to grass at or near breeding. A heifer developed to 51%-58% of her mature weight has a greater chance to gain weight on grass than a heifer at 65% of her mature weight.
Work with your nutritionist, Extension educator or veterinarian on improving your heifer development plan. These early-calving, lower-maintenance females are the ones you want to build your herd upon.
W. Mark Hilton, DVM, is a clinical professor of beef production medicine at Purdue University in West Lafayette, IN.
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