Will R. Getz – Fort Valley State University

In the case of meat goats and most other livestock, traits related to fertility and survivability tend to be lowly heritable. Production traits such as growth rate and milk production (even in meat animals) tend to be moderately heritable, and traits associated with carcass or product and traits related to skeletal dimensions, e.g. mature size, are the most highly heritable traits. Very few studies have been conducted to gather heritability estimates on meat goat populations directly. To do so requires a significant amount of time and herds that are dedicated for genetics research exclusively. Most research centers with a focus on meat goats are not in a position financially to do so. Nonetheless there is little reason to doubt that the values obtained for other species do not also apply to goats.

It is useful to understand that although tables and other sources of information on heritability often cite only one value, be aware that those single values are a composite of the values gained from numerous studies. It is not fixed; it varies from herd to herd and from environment to environment. Heritabiltiy can and does vary among breeds. Therefore, a single study is not adequate to obtain estimates that apply in all cases because the result obtained from any one study reflects the genetics of that population only. Heritability is a population measure, not a value to be associated with an individual. By using the results from several studies, a more accurate sense of the average heritability estimate for any particular trait is obtained.

Heritability is critically important to selection for polygenic traits; those influenced by many genes. We will see later how heritability estimates are a key element in estimating the amount of genetic change that can be expected over time or per generation. Heritability plays an important role in the prediction of breeding values, progeny differences, and producing abilities.

The equations used in prediction of these values are almost always a function of heritability. For example, if we want to predict a doe’s breeding value for number of kids weaned based on evidence from the first parturition (kidding), then we would need to know (or have an estimate) the average breeding value for number of kids weaned in the population, the phenotypic standard deviation in that population (herd or breed), and what would essentially be the heritability in order to have the complete equation.

Traits that are lowly heritable are too often ignored in the plan for genetic improvement, and are changed only through changes in management because more immediate progress can be seen. If lowly heritable traits are important to production, then they should still be included in the plan for genetic improvement because permanent change in those traits will often be critically important. Lowly heritable traits are not to be taken as less important. Certainly female goats that have a higher breeding value for ovulation rate will be more valuable as breeding stock in changing the next generation for that trait.

Very few studies have been completed to determine heritability values for traits in meat goats. There are few herds of meat goats maintained by universities for the sole purpose of conducting breeding research, including estimation of heritability or repeatability values. However because there appears to be some general agreement across species of meat animals, the following table lists some ranges for expected heritability values.

Repeatability

Just a quick note on the matter of repeated records; in meat goats the trait most often the subject of repeated records would be number of kids weaned or the total weight of kid weaned. It is often of interest to use information early in the productive life of a doe, to predict how productive she will be over the lifetime. Measures of repeatability provide a tool for that. One definition of repeatability is that it is a measure of the strength of the relationship between repeated records. Like heritability, it is a population measure and there have not been many published data for meat goats. In dairy goats, lactation yield is a primary trait for which repeatability is important. Repeatability is not a fixed value; it varies from herd to herd, and from one environment to another. Factors that affect heritability tend to affect repeatability in a similar manner. Research institutions rather than individual breeders are the usual source of repeatability estimates. An awareness of the repeatability of a trait can be useful in making culling decisions. When repeatability is high, a breeder or producer is justified in culling poor individuals on the basis of a few early records in the trait. Repeatability is needed for any prediction of probable producing ability in which repeated records are involved.