Section 5. Planning the Breeding Program Darrh Bullock he quality of cattle produced by the beef industry is health programs are examples of environmental effects. determined by the cattle’s genetic make-up and the Environmental effects on economically important traits are environmentT to which they are subjected. Genetic make- controlled through management techniques discussed in the up is under total control of breeders, both purebred and other sections of this manual. commercial, and this responsibility should not be taken The two types of genetic effects on the economically lightly. According to a report from the National Cattlemen’s important traits of beef cattle are additive and non-addi- Association (Beef Business Bulletin, June, 1983), about one- tive. When a bull and cow are mated, each contributes 50 fourth of the calves born in the United States each year are percent of its genetics to their calf. If that calf is then al- of such poor genetic value that they do not produce profits lowed to reproduce, it passes 50 percent of its genetics to for any of their owners—producer, feeder, or packer. each of its calves; however, each calf gets a different sample The selection of bulls and heifers used in the herd and of genes from its parents (that is why brothers and sisters the breeding system used dictate the genetic quality of the are different). The sample of genetics that offspring receive calf crop. The purebred producer uses selection for genetic from their parents and ultimately pass on to their progeny management, while the commercial producer uses both is referred to as the additive genetic effects. These are the selection and mating systems, especially crossbreeding. genetic effects passed on from generation to generation; Selection refers to the breeder’s decision to use some therefore, they are the basis of selection. animals as parents and to cull others. For selection to be Heritability, the percentage of each trait controlled by the most effective, breeders must be able to identify superior additive genetic effects, is an important factor when making animals. This is done by placing emphasis on economi- selection decisions. Highly heritable traits respond more rap- cally important traits that are heritable (see the “Genetic idly to selection, while lowly heritable traits respond more Principles” segment of this section). “National Cattle Evalu- rapidly to management practices (environment) and hetero- ations,” which furnish information (expected progeny dif- sis (crossbreeding). Table 5-1 illustrates the relative herita- ferences) on traits of various bulls, are available from most bility and heterosis of several economically important traits. breed associations and are useful in making selection deci- Non-additive genetic effects refer to how the genetics sions. By using artificial insemination (AI), the average from the two parents combine and how they interact with producer can select a bull of proven breeding value from the environment. The best example of non-additive genetic the “national” herd rather than using one of lesser quality. effects are the benefits realized from crossbreeding. These Because most sires are purchased from them, purebred benefits are known as heterosis. Heterosis is defined as the breeders exert a great influence on the direction of the beef increase in productivity in crossbred offspring over the industry. Commercial producers are insisting that the pure- average of breeds that are crossed. Heterosis is highest for bred seedstock producer keep records and make these lowly heritable traits (such as reproduction) and lowest for records available. It is important that both purebred and highly heritable traits (such as carcass traits). Crossbreed- commercial producers understand and use the principles ing might result in relatively small amounts of heterosis and tools of genetic improvement. for each trait, but these effects tend to accumulate to pro- duce large increases (about 25 percent) in overall produc- Genetic Principles tivity. In some instances a portion of this advantage is passed To fully understand breeding management, it is impor- on to future generations, but, to maximize the benefits, a tant to know some basic genetic principles. Knowing the new breed must be introduced each generation. role genetics plays in each economically important trait of beef cattle can assist in making wise selection decisions. It is necessary to know which traits can be altered through Table 5-1. The Relative Heritability and Heterosis Effects breeding management (selection and/or crossbreeding) and of Several Economically Important Traits in Beef which traits should be altered by other management tech- Trait Heritability Heterosis niques. Birth weight moderate-high moderate Each trait of economic importance in beef cattle is con- Weaning weight moderate moderate trolled by two factors: the environment in which the ani- Yearling weight moderate moderate mal lives and the animal’s genetic make-up. The environ- Milking ability moderate moderate ment consists of not only the weather but how the cattle Carcass traits high low Reproduction low high are managed. Creep feed, forage quality and quantity, and Longevity low high 5—1 Another genetic effect that is important when making less than 100. A weaning weight contemporary group ratio selection decisions is genetic correlations. A genetic cor- of 113 indicates the calf is 13 percent heavier than the aver- relation occurs when you select for one trait and another age of the group with which it was raised. However, a con- trait is affected. The effect of one trait on the other can be temporary group ratio of 113 on one farm may be entirely either complementary or disadvantageous. Here is an ex- different than a contemporary group ratio of 113 on another. ample of a complementary genetic correlation: as selec- Therefore, contemporary group ratios should not be used to tions are made for increased weaning weight, yearling weight compare cattle from different locations or cattle raised un- is also increased. A disadvantageous correlation would be: der different conditions on the same farm. Contemporary as selections are made for increased weaning weight, birth group ratios are the best alternative when EPDs are unavail- weight also increases. Genetic correlations work the same able but should only be used in those circumstances. regardless of which trait is being selected for. In other The best way to determine breeding values for economi- words, as selections are made to decrease birth weights, cally important traits is by using expected progeny differ- weaning and yearling weights are usually decreased, too. ences. The EPDs of two animals of the same breed indi- The implications of genetic correlations for many traits for cate the expected differences in the average performance which expected progeny differences are calculated are dis- of the offspring of those animals. For example, if bull A cussed below (also, see Table 5-4). has a weaning weight EPD of +20 pounds and bull B has a weaning weight EPD of +5 pounds and they are mated to a Understanding Performance large number of comparable cows, under similar environ- mental conditions, a 15-pound difference between the av- Information erage weaning weights of their calves would be expected Performance testing is a helpful tool that takes some (20 pounds - 5 pounds = 15 pounds). In other words, calves guesswork out of the selection of breeding animals. When sired by bull A would weigh 15 pounds more at weaning, purchasing a herd bull or selecting replacement heifers, on average, than calves sired by bull B due to genetics for place emphasis on the genetics that animal will pass on to increased growth to weaning. It is likely some calves sired its offspring, not necessarily on how that animal performed. by bull B would weigh more than some calves sired by bull The easiest, and an often used, method of performance A, but, on average, calves sired by bull A would have a evaluation is simply comparing animals’ actual measure- weight advantage. Expected progeny differences can be ments. Unfortunately, this is a poor method of performance either positive or negative for the measurement in ques- evaluation, and other methods that do a much better job of tion. They are easily used to make comparisons among cattle determining more genetically suitable cattle are often avail- but can only be used to compare animals of the same breed. able. Besides actual measurements, two other types of per- Traits available for comparison vary from breed to breed. formance information are available to producers—contem- They usually include some of the following: birth weight, porary group ratios and expected progeny differences weaning weight, milking ability (expressed as pounds of (EPDs). weaned calf), and yearling weight. Other traits for which Raw or even adjusted figures on most economically EPDs are offered on some breeds are: yearling hip height, important traits are not very valuable in bull selection. For mature hip height, mature weight, carcass traits (hot car- example, if you are considering a bull and all you know is cass weight, fat thickness, ribeye area, and marbling score), that he had a weaning weight of 600 pounds, you don’t scrotal circumference, stayability (measure of longevity), have much to go on. He could have been raised by a heifer calving ease, and possibly others. The following are de- on drought-stricken pasture and have superior preweaning scriptions and implications of selection of some commonly growth genetics, or he could have been raised by a mature used EPDs: cow on lush pasture with plenty of creep feed and actually Birth weight EPD—differences in this EPD reflect dif- have poor genetics for pre-weaning gain. Environmental ferences in the average birth weight of the two animals’ conditions play a large part in a calf’s actual measurements offspring. This is an extremely important EPD, particularly but have no effect on their future offspring.