Body fat content, composition and distribution in Landrace and Iberian finishing pigs given ad libitum maize- and acorn-sorghum-maize-based diets

We aimed to determine whether the dietary carbohydrate source altered body fat composition and distribution in finishing lean (Landrace) and obese (Iberian) swine. To this end, twenty-four finishing castrated male pigs (12 Iberian and 12 Landrace; 108 kg live weight) were offered two diets differing in the main carbohydrates source, maize (diet M) or acorn-sorghum-maize (diet A). Diets were formulated to have the same nutrient content, except for carbohydrate fractions : diet M contained higher amount of starch (537 v. 389 g/kg) but less non-starch polysaccharides (118 v. 148 g/kg) than diet A. At an average weight of 133 kg live weight pigs were slaughtered and their carcasses were sampled to study lipogenesis, backfat and intramuscular fat composition. Iberian pigs showed a higher voluntary food intake than Landrace pigs (3.6 v. 2.4 kg/day; P < 0.001) but no significant differences in the daily weight gain. Diet M tended to promote the highest food intake (P = 0.09). Iberian pigs showed higher (P < 0.01) lipogenic enzyme activities, backfat thickness (71.7 v. 31.9 mm) and intramuscular fat content (40 to 95 g/kg fresh muscle) than Landrace pigs, which was associated with their higher food intake. Furthermore, fat depots from Iberian pigs had higher (P < 0.001) monounsaturated fatty acids (MUFA) and lower (P < 0.05) polyunsaturated (PUFA) proportions than those from Landrace pigs. The backfat thickness of pigs given diet M tended to be higher (P = 0.07) than that of pigs given diet A, without differences in the intramuscular fat content. The higher backfat thickness found for diet M was correlated with a lower PUFA proportion in diet than for diet A (P < 0.001). We conclude that body fat content, composition and lipogenic enzyme activities are markedly influenced by the animal breed and to a lesser extent by dietary characteristics.