Divergent selection for intramuscular fat content in rabbits. I. Direct response to selection.

The aim of this study was to evaluate the selection response on intramuscular fat (IMF) content of LM after 3 generations of divergent selection. Heritability and genetic means for IMF content were also analyzed. Selection was based on the phenotypic value of IMF content measured in 2 full sibs of the first parity. Selection pressure on females was 13% in the base generation and 26% for the next generations. Males were selected within sire families to reduce inbreeding. Line size was 13 males and 83 females in the base population and approximately 8 males and 40 females for high (High) and low (Low)lines in the next generations. A total of 668 records were used to estimate the selection response on IMF. The pedigree file used to estimate heritability and genetic means contained 1,332 animals. Data were analyzed using Bayesian methodology. Differences between lines for IMF were 0.08, 0.10, and 0.09 g/100 g muscle in the first, second, and third generation, respectively. These differences represent a direct and cumulative selection response of 9% of the mean, of which 6.8% was obtained in the first generation. Heritability of IMF content was moderate to high (0.37) with a probability of 97% of being greater than 0.20. The response to selection estimated using an animal model was 0.033, 0.052 and 0.054 g/100 g muscle in line High and -0.032, -0.046, and -0.051 g/100 g muscle in line Low in the first, second, and third generation, respectively. Results of the present experiment confirmed that IMF content can be improved through selection in rabbits.