UNL: Where’s optimum?
January 4, 2018
The use of genetic selection tools by cattle breeders has resulted in significant changes within the majority of popular breeds over the last 30 years. With a few exceptions, the overwhelming genetic trend for milk, weaning weight, and mature weight over that time has been for more. Without question, the use of Expected Progeny Differences (EPD) has enabled this change. The question at hand, however, is "have we selected towards that which is optimal?" The late Dr. Bob Taylor from Colorado State University said it well, "Profitable cattle are usually productive, but productive cattle are not always profitable."
Four different benchmark data sets for commercial cow-calf producers from the states of Minnesota, North Dakota, Kansas, as well as Texas, New Mexico and Oklahoma have shown little to no change in average weaning weights or calf weaning rates in terms of the percentage of calves weaned per cow exposed over the last 15 years. This has to prompt the question why? How can it be that there has been such significant genetic change in several breeds that should increase weaning weights, but records from several commercial cow-calf data sets would indicate that there has been relatively no change?
In 2014, Dr. David Lalman from Oklahoma State University made a presentation at the Applied Reproductive Strategies in Beef Cattle meeting titled "Matching Cows to Forage Resources in a World of Mixed Messages." In that presentation, Dr. Lalman made the case that the genetic potential of many cattle today are beyond the nutrient levels that are provided by forage resources thus hindering the ability of animals to express their genetic potential. He presented data that would indicate that the cost of maintaining larger cows with higher milk potential exceeds the value produced by small increases in calf weaning weights.
In 1988, Dr. Rick Bourdon, wrote a paper titled "Bovine Nirvana – From the Perspective of a Modeler and Purebred Breeder" where he presented the case that genetic selection should be toward the optimum for what a set of resources or environment could support. Dr. Bourdon stated, "To breed for optimum means to have a target insight beyond which you don't want to go. If your goal is to maintain an optimum level for any trait, the evidence of your accomplishment is not visible change, but lack of it."
Cow-calf producers have EPDs and index tools to make genetic selection decisions related to traits that impact levels of productivity and longevity. Producers selecting sires from which to develop replacement heifers would be well served to evaluate where their cow herd is compared to what they believe optimum to be. Producers can work with beef cattle genetic specialists and breed association representatives to help them identify what EPD levels for milk, weaning weight and mature weight best meet their target. What a producer identifies as optimum in terms of milk production, weaning weight and mature size can vary significantly from one operation to another depending upon resources available and management. When optimum is identified, sires can be selected to produce daughters whose maintenance energy, longevity, level of milk production and mature weight will move the cow herd toward identified goals given available resources.
Identifying and selecting optimum genetics for milk production and mature weight is a genetics selection approach that may require a change in focus for many cow-calf producers. It may mean selecting sires at a bull sale that are at or below breed average to move the cow herd genetically toward a desired level for certain traits. Selecting a bull that is "below breed average" is a paradigm shift for many cow-calf producers. Identifying a window of optimum given a set of resources and then selecting cattle that hit the optimum target is the goal under this method of cattle breeding. Success in selecting for optimum means that for many producers they will be selecting sires whose EPDs for milk production and mature weight will decrease the average in their herd. Simultaneously, they should be using EPDs to select for traits that will maintain or improve fertility and longevity. Genetic selection and breeding programs should focus on increased profit, and in many cases this may mean selection for decreased mature weight and milk production to move future replacements for the cowherd towards optimum.
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