Principles of Selection

Principles of selection.

Goats, like other types of livestock, can benefit from controlled breeding and selection to improve specific traits. To achieve this improvement and realize increased performance, it is critical that producers have an understanding of some of the basic principles behind genetics and how to utilize performance records to make progress.

The first step is to remember that there are two components to all traits that we see: genetics and environment. Producers have some control over both of these and each is important in improving performance. It is critical that animals have access to proper nutrition and health care to reach their genetic potential. It is also important to remember that animals raised in different environments may look similar but their offspring may not perform the same at your farm. This is why we cannot directly compare individual performance data between locations. We need to compare individuals only within a contemporary group — of similar age, sex, management and location — to make more accurate comparisons than those based on individual records alone.

In the book “Animal Breeding Plans,” by J.L. Lush, there are three aids to selection that are still relevant today: pedigree, lifetime averages and progeny testing. Today we have better methods to estimate the genetic value of an animal than those available in 1945, the date of the last edition of his book. However, because expected progeny differences are not readily available for goats, the methods discussed by Lush are still our best options.

In his book, the use of lifetime averages or individual data was considered the way to make the most progress if selecting within an environment. He stated that the use of individual performance, especially if multiple measurements were used to reduce environmental influences, was the most effective single source of information for genetic improvement. Goat producers can practice this type of selection through the collection and use of production records. Essentially, goats that perform the best on a specific farm are selected to be parents of future animals on the farm.

Lush states that pedigree selection can be an effective method of selection if the producer knows enough about the animals in the pedigree. He also states that most producers do not have the time to learn enough, and the pedigrees themselves do not provide enough other information. The information available in pedigrees in 1945 was limited to parentage and in some cases show results. Only dairy cattle breeds tried to include some basic production information. Today we have multiple generations of information on goat pedigrees, but often they have only show or classification data.

As the goat industry moves to performance pedigrees, similar to the cattle industry, this lack of data may change. However, until we have expected progeny differences available on most goats, we need to be cautious of using pedigrees alone. Lush puts it this way: “In most commercial pedigrees, other than those for dairy cattle and poultry, little information of any kind is included except the names and identifying numbers of the animal. Such a pedigree is useful only to the extent that one knows or can find from some other source how meritorious or mediocre those ancestors were.” This is very true for goats today. Dairy goat breeds generally have some indication of milk potential available while meat goats only list parentage and possibly livestock show information.

Progeny testing is another very important method of evaluating animals for genetic merit as parents. However, the number of animals that need to be maintained and the cost of this procedure make it very difficult and expensive for people to utilize. Fortunately, today we have the ability to utilize information from relatives and an individual’s own performance to calculate genetic merit. Several goat breed associations have started to collect the necessary data to utilize this information and help producers select better replacements through sound information. The use of expected progeny differences has been widespread in beef cattle and resulted in tremendous gains in performance through targeted selection by producers at all levels. The same gains can be achieved in the goat industry if these tools are made available.

Today, the most practical way for goat producers to evaluate animals in most cases is the use of the individual’s own performance. This performance needs to be adjusted for known differences due to age, age of dam and type of birth to allow for the most accurate selection. These adjustment factors are known and available from different sources. One caution with individual records is that they are most useful in comparison between animals that are raised in the same environment, for example, bucks on the same buck test, does from the same kidding season and herd.

Reference: Animal Breeding Plans. J.L. Lush. Third Edition. The Iowa State College Press, 1945.