Replacement heifers represent the future of the cow-calf operation. These females are the genetics behind the next generation of farm offspring. Efficient development is critical as raising a replacement heifer represents a significant asset that does not generate a return until the first calf is sold.
Beef herd productivity is increased when a high percentage of the heifers are bred early in the season. Heifers have higher rates of calving difficulty when compared to mature cows. Yet, there are some management tools that can be used to identify and minimize risk factors for dystocia.
Lifetime productivity is also an important consideration in planning the female development timeline. Heifers calving at 24 months of age produce an earlier return on investment and potentially have more calves than females who are older at calving.
Targets for the beef replacement heifer program are: increase / maintain a high conception rate early in the breeding season, minimize dystocia rate, promote good post-calving conception rates, and increase farm income through efficient lifetime productivity. To achieve these goals, we must utilize a plan that addresses rate limiting steps or critical control points during each production phase. From birth to calving, heifer production can be divided into six key phases: pre-weaning, weaning, pre-breeding, breeding, mid-gestation, and calving.
Knowledge-based management of replacement heifers is based on good production records and the process is initiated with the birth of the animal. Individual identification allows not only performance, but pedigree tracking on the calf. Recording birthdates or at least birth week is useful because heifers born early in the calving season will have an age advantage relative to females born at the tail end of the season.
Weaning is the time to begin the immunization program and determine a nutritional plan based on animal performance. The goal with weaning vaccinations is to protect animals against common respiratory pathogens and also to begin building immunity against pregnancy wasting infectious agents.
Weaning weight can be used to determine a nutritional program necessary to meet animal target weight by the goal breeding date. The onset of puberty is heavily influenced by both age and weight. To become pubertal by yearling age (12-13 months), heifers must receive adequate nutrition to signal the body that the "luxury" of reproduction is available. As a rule of thumb, target breeding weight can be calculated as 65% of the expected mature female weight. Thus, by subtracting the weaning weight from the target weight and dividing by the number of days between weaning and breeding, a goal for the rate of gain can be calculated. Achieving target weights prior to the onset of the breeding is key to achieving the goal of having a large number of heifers conceive early in the season.
Sire selection is an important decision impacting dystocia rates and offspring performance. Many breeds offer birth weight and calving ease (difficulty) expected progeny differences (EPDs), and veterinarians can offer a valuable service by helping clients select a bull appropriate for their operation. Birth weight and weaning weight are correlated - resulting in a common misconception that producers must choose between dystocia and reasonable weaning weights. Utilization of artificial insemination (AI) allows the farm manager to select a bull with the relatively rare combination of a low calving difficulty due to birth weight and a high growth performance potential.
Replacement heifer development is a critical component of many cow-calf operations. There are a variety of tools that greatly increase the efficiency and value of the bred heifer for the farm manager. Veterinarians can play a key role with clients by identifying and assisting with evaluation of critical control points in the heifer development program.