Direct and Correlated Responses of Selection in Divergent Selection for Intramuscular Fat in Rabbits

The objective of this study was to evaluate the genetic response for a divergent selection experiment on intramuscular fat (IMF) content and to estimate the correlated response in carcass and meat quality traits. Data from two generation of selection were used in this study. The base population was composed of 13 males and 83 females. High (H) and Low (L) lines had 8 males and approximately 40 females each one per generation. Selection was based on the average phenotypic IMF value of two full sibs measured in Longissimus muscle (LM). Two rabbits (male and female) of the first parity of each doe were slaughtered at 9 weeks of age. The following traits were recorded: live weight (LW), hot carcass weight, chilled carcass weight, reference carcass weight, scapular fat weight, perirenal fat weight, meat/bone ratio of hind leg, pH of LM, colour (lightness, L*; redness, a*; yellowness, b*) of the carcass and LM. Longissimus muscles were excised from the carcass and the IMF content was measured by near infrared reflectance spectroscopy. Data were analyzed using Bayesian methodology. Response to selection was estimated by the difference between H and L lines. The difference between lines for IMF content in the second generation of selection was 0.11 g/100g, which represents a direct response to selection of 9.8 %, of which a 6.8 % was obtained in the first generation and a 3 % in the second. There seems to be a negative correlated response on live weight, carcass and adipose tissues weights, with higher values in L line. However, the evidence for adipose tissue is rather weak. There is no evidence of changes in carcass and meat colour measurements as well as in meat/bone ratio and muscle pH.