Three generations of selection for lean growth in Landrace pigs using culling levels and migration has been practiced. Two traits were under selection; 168-day weight and ultrasound backfat thickness at 105 kg. Replicated select and control lines were developed from two base populations in 1990. Adjusted weight at 168 days of age was the first culling criterion. After boars and gilts with unacceptable 168-day weights were eliminated as selection candidates, the leanest seven boars and 24 gilts were kept to produce the next generation of select line pigs. A control line boar was randomly chosen from each of eight control sire lines. One replacement gilt was randomly chosen from each control line litter. Matings were made within each line and replicate to minimize the level of inbreeding in the next generation. In the select line each generation, four of the 24 gilts selected were randomly chosen and artificially inseminated using semen from one Landrace boar which was available at a commercial boar stud. There were no overlapping generations. Different boars were selected from the boar stud each generation. Growth rates and backfat thicknesses were recorded on 1,331 boars and gilts. Longissimus area and l(P-rib backfat thickness were collected on 170 carcasses from barrows slaughtered at 102 kg. A multiple-trait DFREML algorithm was used to analyze growth rates, backfat thickness and the carcass traits. The multiple-trait model for growth rate and ultrasound backfat thickness included fixed effects for replicate, generation and sex and random animal and litter effects. The carcass traits were analyzed with a multiple-trait model with fixed effects for replicate, generation and a hot carcass weight linear covariate and random animal effects. The inverse of the numerator relationship matrix was included in all analyses. After three generations of selection, differences between average breeding values in the select and control lines were 5.37 kg for 168-day weight and -0.26 cm of backfat thickness. Differences in average breeding values between the two lines were -0.37 cm for lO^-rib backfat thickness and 2.3 cm2 for longissimus area.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 91–94, 1994
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