December 2011 Articles

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Replacement Heifers - A Strategy for Success

Replacement Heifers - A Strategy for Success Source: University of Arkansas Division of Agriculture, Brett Barham
Traditionally, many cattlemen have selected replacement heifers based largely on which heifers look the best.While this selection practice emphasizes genetics for growth and tends to pick heifers from the earliest-calving cows, it may not result in sufficient focus on genetics for expressed fertility, calving ease, optimum levels of milk production, sensible maintenance requirements and adequate longevity. Present-day genetic information affords producers the ability to produce and select replacements with a higher likelihood of success, as compared to traditional approaches. What Makes a Successful Replacement Heifer? What does a replacement heifer need to do in order to achieve production success? Most producers would agree that successful replacements:
reach puberty and become pregnant early in the first breeding season;
calve unassisted each year;
breed back early in the second breeding season as wet two-year-olds, with high levels of sustained fertility thereafter;
have optimum milk and fleshing ability, so as to wean profitable calves yet maintain sufficient body condition for early annual rebreeding;
have sensible maintenance requirements as a result of mature size and milk production levels which are matched to available feed resources;
have sound teats, udders, feet and legs as well as calm temperament and as much longevity as possible to minimize annual replacement rates;
represent genetics for optimum levels of growth, efficiency and carcass merit for the purpose of producing profitable feeder and fed cattle as well as replacements; and
possess high salvage value so as to offset replacement costs.
Given the demanding list of attributes required of replacement heifers, it is useful to consider how genetic information might be used to select for success. Opportunities to take advantage of genetic information exist at three points of heifer production:
When sires are selected to produce replacement heifers
When heifers are selected from the pool of replacements
When sires are selected to breed replacements
Selecting Sires to Produce Replacements The better the pool of potential heifers from which to select, the better the odds of selecting a productive group of replacements. For commercial cattlemen, there are at least two keys to producing a superior pool of replacements: 1) a well-designed crossbreeding program that generates maternal heterosis and uses breeds well adapted to the production environment and 2) use of EPDs to select sires with genetics for the combination of items listed above. Choosing which breeds to use in crossbreeding starts with an evaluation of your present cowherd and feed resources, as well as a determination of the targeted end-product market. Selecting breeds from which to produce replacements should also go beyond evaluation of only puberty and level of milk production. Selection should include consideration of breed comparison data related to maternal calving ease, calf vigor and survivability, cow maintenance energy requirements, mature cow size, optimum milk production, convenience traits such as teat and udder soundness, longevity and traits contributing to life cycle production efficiency. Selecting Replacements Heifers In addition to known pedigree and performance information from the sires and dams of replacements, performance data can be collected from yearling-age heifers when they are processed prior to breeding as part of the herd health program. Collection of the following information can help guide selection of heifers toward genetics for early puberty, maternal calving ease and growth, as well as moderate mature size and adequate fleshing ability. Reproductive Tract Scores - The reproductive tract scoring system estimates a heifer's pubertal status via rectal palpation of the uterine horns and ovaries. Track scores range from one to five, with heifers scored as four and five believed to be cycling based on the presence of a corpus luteum or large follicle on the ovaries and good uterine tone. Heifers scored as three are thought to be on the verge of cycling, while those scored as one and two have more infantile, less developed reproductive tracts and are not yet cycling. Research has indicated that heifers scored as three, four or five generally have higher pregnancy rates and earlier conception dates compared to heifers scored as one or two. In addition to serving as a heifer selection tool, reproductive tract scores can be used to determine if a group of heifers is sexually mature enough to respond favorably to a synchronization and A.I. program. Palpation of the reproductive tract can identify freemartins or heifers that might already be pregnant prior to the start of the breeding season. Many large animal vets can evaluate reproductive tracts of replacement heifers.
Pelvic Measurements - Calving difficulty primarily occurs among first-calf heifers as a result of "heavy" calf birth weight in relation to the size of the dam's pelvic area. While birth weight is unquestionably the key direct factor related to calving ease, pelvic area appears to be the highest ranking maternal variable. Colorado State University research has shown that as birth weight of calves increases & pelvic area of replacement heifers decreases, the incidence of assisted births also increases. Depending upon the average pelvic size of the group, culling heifers with the smallest pelvic areas (i.e., smallest 5 to 10 %) has been shown to help reduce the incidence of assisted births. Yearling Weight, Hip Height and Condition Score - Weight, height and condition information can be used to select heifers with adequate early growth and fleshing ability but help avoid selecting heifers that might be too big and hard fleshing later in life. Avoiding heifers that are too extreme - either excessively big or small - is expected to contribute to greater cowherd uniformity. "The accuracy of replacement heifer selection can be improved by combining these yearling data with knowledge of pedigree information from sires and dams for appropriate levels of maternal traits (i.e., milk) and longevity, with incorporation of a visual evaluation of soundness and doing ability." Selecting Sires for Replacement Heifers While the first test of a replacement heifer is becoming pregnant early in the first breeding season, the next major hurdle is the heifer's ability to give unassisted birth to a live, vigorous calf. In addition to avoiding production and selection of heifers with genetics for high birth weights themselves, selection of service sires on the basis of their EPDs for low birth weight, high expected calving ease and short gestation length is the most reliable way to minimize calving problems. Calving ease in first-calf heifers is also related to reproductive performance during the second breeding season. Research has demonstrated that heifers that do not require assistance at calving tend to have higher pregnancy rates following the second breeding season by 3 to 5 percent and are about a week earlier in terms of day of second calving, as compared to heifers that require assistance. This is most meaningful when you consider that the number one reason cows are prematurely culled at young ages is because of reproductive failure (open at the end of the breeding season). Implementation of an A.I. program and synchronization, whereby sires can be reliably selected for calving ease in addition to adequate performance in other traits, is the most sure-fire way to genetically manage for a successful first calf from replacements. Through the use of A.I., unique service sires can be used that not only minimize calving difficulty but also pass on genetics for the desired combination of maternal, growth and carcass merit. Considerable risk can be managed through the use of synchronization and A.I. in replacement heifers. Summary Successful replacement heifer selection begins with wise selection of the sires from which heifers are produced. Once a superior pool of replacements is developed, use of performance information collected on yearling heifers, as well as information known about the sires (or group of sires) and dams of heifers, can be used in conjunction with visual evaluation to improve the odds of selecting the most productive heifers. Finally, smart selection of sires to breed to heifers can help ensure calving ease and production of a profitable first calf from replacements. Through planned crossbreeding and disciplined use of available genetic information, heifers can be produced, selected and bred with more confidence and less risk, as compared to traditional practices. Source: Dr. Kent Anderson, North American Limousin Foundation