Cattle breeders have used genetic selection tools to change the majority of the major breeds significantly. Producers want to increase productivity and longevity of their herd to increase profitability.
Although, other modalities -- including artificial insemination, embryo transfer and cloning -- have been adopted by some producers, natural service continues to be the main means of increasing genetic potential of cow-calf herds.
The majority of genetics comes from sire selection. A bull can sire 25-45 calves via natural service or several hundred with artificial insemination in a year, whereas a cow can have one calf naturally a year or 20 calves via embryo transfer. Superior genetics is spread quicker via the bull.
Cow-calf producers use expected progeny differences and index tools to make genetic selection decisions related to traits that impact levels of productivity and longevity. Expected progeny differences on bulls have greater accuracy than cows due to the number of prodgeney. Expected progeny differences are the predicted performance of a bull's calves compared to the calves of a bull with an expected progeny differences of zero.
Specifically, differences in expected progeny differences between two individuals of the same breed predict differences in performance between their future offspring when each is mated to animals of the same average genetic merit. Expected progeny differences are calculated for birth, growth, maternal and carcass traits and are reported in the same units of measurement as the trait (normally pounds). Their values may be compared directly only between animals of the same breed to select genetics that will increase the productivity and longevity of the herd.
Selection of the proper replacements is important to increase the genetic potential of the herd. Selection criteria for replacements fall into the same categories as expected progeny differences: birth, growth, maternal and carcass traits.
After the bull, much of the attention -- and rightfully so -- has been placed on the replacement of heifers. Using parentage as a criteria for selection for replacements will help the selection process. Eliminating heifers from cows that do not possess the traits that are desired for the herd allows for any easy selection criteria. For example, identify cows within the herd that you do not want to keep their offspring due to aggressiveness or other traits not desired.
Every rancher has a vision of "ideal" phenotype. Select animals with that phenotype will over time allow you to have a herd with that phenotype. An important criteria for selection of heifers is to keep heifers that are older or born early in the calving season. Research shows heifers that become pregnant early have greater longevity, wean more and heavier calves compared to heifers that become pregnant later in the breeding season.
Remember always to cull automatically any freemartin heifers (females born twin to male calves) due to the likelihood of infertility. Using growth rate from birth to weaning and/or weaning to yearling age is a selection criteria practiced by some producers. Caution must be used not just to select the biggest heifers at any given point in time. Avoid selecting the extremes to move your potential mature weights away from your "ideal" weight.
Heifer tract scoring and pelvic measurements by a veterinarian can evaluate the heifers reproductive tract and identify heifers with a narrow pelvic area that might go onto having calving difficulty. Heifer tract scoring and pelvic measurements usually are performed 45 days before the breeding season.
The genetic changes in the herd can be accelerated with many of the new modalities such as artificial insemination, embryo transfer and cloning. Although these modalities involve more intense management and input cost, changes in the genetics of a herd can be reached in a shorter amount of time with the right selection.
There are many tools to improve performance and productivity through genetics. Taking steps to reach the genetic goals of your herd can be done through proper decisions of culling and breeding, but it's important to note the best genetics in the world will not make a difference unless the proper environment is provided to allow those genetics to prosper.