Abstract
ABSTRACT: The objective of this study was to evaluate, through data simulation, the impact of restrictions on the maximum number of full- and half-sibs selected for males and females on the level of inbreeding and genetic gain of the herd. Data came from real populations A and B, composed of Pietrain and Landrace breed pigs, respectively. To generate the simulated populations, a Fortran-language simulator was developed using the (co)variances of the breeding values and the productive and reproductive rates obtained from populations A and B. Two data files were created. The first contained the pedigree of the previous 10 years, with 21,906 and 251,343 animals in populations A and B, respectively. The second included breeding values for age to reach 110 Kg body weight, backfat thickness, and feed conversion, for both populations; longissimus dorsi muscle depth, for population A only; and number of live piglets at the 5th day of life per farrowing, for population B only. Three scenarios were simulated with ten generations by varying the restrictions on the number of full- and half-sibs selected for males and females, with 30 replicates per generation and scenario. Regardless of the mating strategy used in a closed production unit, there is an increase in inbreeding levels. Inbreeding increases are larger in populations of smaller effective size. Restrictions on the number of full- and half-sibs selected are effective in reducing increments in inbreeding. Restriction to a maximum of two full-sibs and three half-sibs for males and three full sisters for females provided the highest genetic gains.
Highlights
As with other species, pig breeding programs work with closed elite herds, which makes inbreeding an important issue
Process of selection based on genetic evaluation using animal models, whose accuracy is increased through the addition of information of parents, elevates chances of co-selection of relatives, which leads to increased inbreeding and a reduction
Additive genetic value of each animal of the generation was obtained as follows: in which z represents a random value obtained from a normal standard distribution – N~(0,1)
Summary
Pig breeding programs work with closed elite herds, which makes inbreeding an important issue. Geneticists are aware of the depressive effect of inbreeding and do not deliberately use this practice with their herds. The second hypothesis, of over dominance, states that heterozygotes are superior to both homozygotes and the decreased frequency of heterozygotes due to inbreeding reduces the opportunity of expression of this heterozygotes (CHARLESWORTH & CHARLESWORTH, 1999). In addition to these two hypotheses, a third one has been proposed by TEMPLETON & READ (1994) whereby inbreeding depression is a consequence of the disruption of the epistatic interaction between the loci, caused by inbreeding
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