Traits with Intermidiate Optimums
Genetic selection is often thought of as a process whereby genetic potential is always increasing for all traits and animals within the herd. In reality, there are often situations where a breeder should strive to maintain current levels of production or to limit increases in production. Situations where this philosophy applies include traits with intermediate optimums. To illustrate this concept, consider direct calving ease. We want heifers to calve unassisted because calving difficulty creates problems in rebreeding and can result in losing a calf or the dam. However, we don’t want the genetic correlation with birth weight to result in smaller than necessary calves, because calves that are too small might have lower survivability, particularly in adverse weather conditions, and have more weight to gain by weaning to achieve performance levels comparable to their higher birthweight contemporaries. In these cases, the focus should be on optimizing genetic potential for the prevailing environmental conditions and management limitations, rather than focusing on maximum output.