Pigs to Pork
Selection
Swine Evaluation and Testing Programs
K. J. Drewry, Animal Sciences Department
AS-351 Sept. 1966
Introduction
Commercial and pure bred swine producers in the United States are currently being offered several types of programs to be used in evaluating the productivity of their swine herds. The mechanics of the various programs may, at first, seem to be quite different. However, the primary objective of each program is to improve performance for such economically important traits as reproductive performance, sow productivity, struct tural soundness, growth rate, feed efficiency, backfat and carcass quantity and quality. These objectives will be met only if the superior producing animals are accurately identified in the various programs and are made available to swine producers.
Types of Programs
Heritability, the amount of difference of a trait which is from the "building block" genes passed on by the parents, ranges from 10 to 15 percent for reproductive traits to 30 to 40 percent for growth or production traits, to 60 to 70 percent for carcass traits. A summary of heritability estimates for several swine traits is presented in Table 1. Research indicates that, with traits of low heritability and traits which cannot be accurately measured on the individual, maximum genetic progress is made when selections are based on individual, litter and progeny records. However, when the trait can be measured on the individual and is medium to high in heritability maximum genetic progress results when selections are based on the individual's own performance.
The various swine evaluation and testing programs may be classified into broad categories of: (1) individual testing, (2) litter testing, and (3) progeny testing. These classifications have been developed because of the several methods of selection (pedigree, individual performance, litter performance, and progeny performance) and types of selection (tandem, independent culling levels, and index of net merit).
Rate of Genetic Improvement
Four factors which affect the rate of genetic improvement are: (1) heritability,
(2) selection differential, (3) genetic association among traits and (4) generation interval.
Genetic associations among traits may be favorable or unfavorable. Research indicates that with economically important traits these associations are favorable. For example, by selecting faster gaining animals one will also be selecting more efficient animals.
Selection differential or reach is the measure of how diligent the breeder was in his selections of herd replacements. The reach is determined by the percentage of the progeny needed for replacements, the number of traits considered, and the differences which exist among animals in the herd.
More selection pressure or reach is post sible in the males than in the females, since