From CVC IN KANSAS CITY PROCEEDINGS, Aug 01, 2011
By Grant Dewell, DVM, MS, PhD
The heifer selection program is a vital aspect of a commercial cow-calf operation. Since replacement heifers represent the future potential of the herd, successful replacement programs are a high priority item requiring careful attention by the ranch manager. Unfortunately, for many producers, the heifer selection process is reduced to a ten second decision at weaning before the calf is released from the squeeze chute. The beef cattle veterinarian can be an integral part of the production team by focusing management on crucial areas.
A successful heifer selection programs begin after the producer has specific written goals in place for the operation. For example, if producing calves that excel on a carcass grid is a primary goal, then a terminal cross program may be optimal. With this objective, a producer would have to derive replacement females from outside sources. If maintaining a purebred operation is important, then crossbreeding for hybrid vigor would not be an option. Helping your clients define achievable production goals is the first step in the replacement heifer selection process. Once the operation has specific objectives in place, then the current herd can be evaluated and a selection program implemented to help attain the goals.
The replacement heifer program should select for females that have desirable genetic traits, meet phenotypic specifications and will be profitable for the operation. Proper attention in these areas will assure a good replacement heifer program.
The dairy cow’s very defined purpose has enabled the dairy industry to experience rapid advances within their genetic base. The dairy producer selects almost exclusively for milk production, a trait that has both high heritability and reflects the purpose of the dairy cow. In contrast, genetic selection in beef cattle is primarily based on performance of the calf. While these traits do have good heritability, they are not as well defined as milk production because there is often no clear picture of what the final product should be (weaning weight, yearling weight, rib-eye area, marbling, etc.). The confounding problem is that calf performance is actually not the purpose of the beef cow. The beef cow should be selected to produce and wean calves. Relevant traits include fertility, longevity, mothering ability and health. These traits are best achieved through heterosis with a planned crossbreeding program.
Many producers limit genetic selection for maternal traits to calving ease (CE) and milking ability, which are really not maternal traits. Caving ease is primarily related to birth-weight, which is actually a growth trait. By selecting for calving ease, long-term production is lowered because we are actively selecting against growth. Milking ability, similar to dairy cattle, is a growth trait. Its purpose in beef cattle is to increase weaning weight of calves, which is measurement of growth or calf performance. Too much emphasis on increased milk production may result in negative affects on calves and cows. For the lactating female, milk production is an obligatory drain on the system that may lead to poorer reproductive performance due to a high-energy demand and resulting deficit in body condition. In general, most females on range operations are limited in milk production from a nutritional base rather than their genetic potential.
One trait that can be selected for and result in positive returns is puberty. Early puberty females are more likely to conceive in the first part of the breeding season, therefore calving at the onset of the calving season. These heifers will then have a longer postpartum period before the breeding season and will be more likely to continue to settle early throughout their reproductive tenure. Age at puberty is positively correlated with pregnancy percentage and milk production and also enjoys a slightly positive correlation with growth traits. Presently, this trait is probably the best proxy for fertility. A veterinarian that understands the reproductive and production consequences of genetic traits can help clients focus their genetic program.
Many veterinarians have limited their input into heifer selection to measuring phenotypic traits such as weight, frame score, pelvic measurement, and reproductive tract scoring. Many of these are production-based benchmarks to establish a uniform group of heifers instead of enhancing fertility. Although frame score can be used to prevent cow size from increasing, selection of bulls should have already factored this in. All of the previously mentioned traits are also influenced by the age of the calf.
Older calves will have had more time to achieve their optimal pre-breeding weight (65 % mature weight), their frame and pelvic size will be bigger, and many will have begun to cycle. These older heifers will not only have reached puberty and be cycling but should have cycled several times, which will increase their conception rate. Long-term affects of selecting older heifers to enter the replacement program include improved rates of early conception, less dystocia, and more days to resume cycling prior to the start of the next breeding season. These females will be more apt to conceive regularly and remain early calving cows. Veterinarians will influence that optimal replacement heifer selection by shifting from strictly measuring phenotypic production parameters to providing additional counseling to clients on interpretation and application of measurements.
Decreased profits have caused many beef cow operations to exit the industry. One contributing factor to the decline in operations is the continuous expense of replacement heifers that have a poor or negative return for the investment. Although increased growth traits have been selected for years, profitability has not increased along with it. A profitable cow may be defined as one that weans a calf every year until she pays for her replacement cost (Table 1). In general, this takes five to seven years in most operations. The average age of the beef cowherd is approximately five years, indicating that many replacements are leaving the herd before they pay for themselves. Many of these culled females exit the herd after only weaning one or two calves (Table 2.). This increases the financial burden on the remaining cows, leading to a lowered return on assets.
These tables illustrate the important fact that replacement females need to wean a calf every year if they are going to be a productive member of the cow herd. Fortunately, it is possible for replacement heifers to be profitable. Utilizing a planned crossbreeding program to achieve a high degree of heterosis will contribute to improved fertility and longevity of the female. Genetic selection for age at puberty will help to positively influence fertility and improve long-term retention of females. Strict selection of early born heifers will also assure that replacement females are ready to be future profitable producers for the cow-calf operator. The beef cattle veterinarian can play a vital role in helping their clients select profitable replacement heifers.
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