Building and Selecting Replacement Heifers
For cow calf producers that sell their calves at weaning, reproductive performance has five times more impact than growth and ten times more impact than carcass traits on the profitability of their enterprise. Therefore, building and selecting replacement females which have superior reproductive traits has a huge impact on the economic viability of a cow calf operation. The key traits that impact reproductive performance are fertility, longevity, calving ease, amount of milk, docility, mature weight, and growth to weaning and/or yearling endpoints. Other attributes may include coat color, polledness breed or breed combinations to generate maternal heterosis.
Most commercial heifers will not have Expected Progeny Differences (EPDs) for the above mentioned traits, and some of these traits are lowly heritable they are largely influenced by the sire selection that occurs in a herd over time. Repeated selection for growth and milk can result in females that can’t meet their nutritional needs on forage resources provided and require more feed resources to calve on an annual schedule. In other words the sire that produces the best terminal calves may not be the sire of choice for replacement females.
The American Angus Association provides a valuable tool for evaluating nutrient availability and selecting optimal ranges of Milk EPDs for sires of replacement heifers at http://www.angus.org/Performance/OptimalMilkMain.aspx. Use of selection indexes that heavily weight terminal traits are strongly discouraged for use as selection tools for sires of replacement heifers.
Heifers that represent optimal combinations of breeds known for superior maternal performance are a better alternative to straightbred heifers of equal quality. Maternal heterosis has been demonstrated in numerous studies to be very beneficial to commercial cow-calf production. About two-thirds of the economic benefit of crossbreeding comes from having crossbred cows and one-third from having crossbred calves.
The bulk of the benefit of maternal heterosis is driven by improved maternal calving ease, fertility, and longevity of crossbred females. First cross (F1) crossbred cows typically last about 1.5 years longer in herd and have 23-30 percent improvement in weaning weight per cow exposed thus improving production efficiency dramatically.
Ideally replacement female selection should start with selection of sires. Sires should be selected to produce heifers that meet the replacement female breeding objective outlined above. Use of fixed time AI to proven sires with high accuracy EPDs for maternal traits makes for an effective breeding/selection system that works well in tandem with using a terminal bull as a terminal sire. It is important to select sires to produce replacements that optimize traits of cows so they fit a livestock producer’s production environment.
