Selección divergente por contenido en grasa intramuscular conejo

Abstract

A divergent selection experiment on intramuscular fat (IMF) content was performed in rabbits during eight generations. Selection criterion was the averaged phenotypic value of IMF measured in Longissimus dorsi (LD) muscle at 9 wk of age in two full-sibs of the candidate. The aim of this Thesis is to evaluate the direct response to selection for IMF and the correlated responses in other meat and carcass quality traits. Divergent selection for IMF was successful. Direct response to selection in the eight generation was 2.4 standard deviations (SD) of the trait, which represents a genetic progress of 5% of the mean per generation. Genetic trends were symmetrical for both lines. Correlated responses to selection were measured from fifth to eighth generations. Fatty acid composition of LD was affected by selection for IMF. High-IMF line showed greater monounsaturated (MUFA) but lower polyunsaturated (PUFA) fatty acids percentages, and their individual fatty acid percentages showed similar correlated responses, except for C18:3n-3 that was greater in the high-IMF line. We did not find differences between lines for saturated fatty acid (SFA) percentage, but C14:0 and C16:0 percentages were greater in the high-IMF line, and C18:0 was greater in the low-IMF line. A positive correlated response to selection for IMF was observed in the IMF content and fatty acid composition of other muscles with diverse oxidative pattern (Biceps femoris, Supraspinatus and Semimembranosus proprius). Protein content of LD that was greater in the high-IMF line, whereas we did not observed differences between lines in colour and pH meat quality traits. Instrumental firmness was 9.9% greater in the low-IMF line than in the high-IMF line, whereas we did not find differences between lines in other instrumental texture parameters and cooking loss. No effect of selection for IMF was observed in any sensory attribute. Regarding carcass quality traits, a positive correlated response to selection for IMF was observed in carcass fat depots, whereas we did not find differences between lines in other traits. Genetic parameters for IMF and some of the meat and carcass quality traits cited above were estimated and corrobated with the phenotypic responses to selection observed. In this Thesis, we also studied the lipid metabolism of the divergent lines. High-IMF line showed greater glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (EM) and fatty acid synthase (FAS) lipogenic activities in glycolytic LD muscle than low-IMF line, and greater G6PDH and FAS activities in the oxidative Semimembranosus proprius muscle and perirenal fat depot. However, differences between lines were observed only at 13 wk of age and not at 9 wk. Catabolic activities in muscle involved in the lipid metabolism did not explain the differences between lines for IMF. Liver size, which is the main lipogenic tissue in growing rabbits, was greater in the high-IMF line and showed greater G6PDH and EM activities than low-IMF line at 9 wk, although differences for EM were not relevant.; Se…