The influence of changes in dietary fat and oils on fatty acid profiles of carcass fat in finishing pigs

Abstract

The influence of dietary fat source on gross carcass composition and the rate of change of carcass fatty acids in growing–finishing pigs was studied. Three sources (Rape seed oil, R; Soya bean oil, S; Tallow, T), were included into iso-caloric and iso-nitrogenous grower and finisher diets at rates of 60, 60 and 65.5 g/kg. Diets were fed from 25 to 55 kg live weight. Thereafter, until 92.5 kg, treatments were either a continuation of the grower phase or a change to one of the other diets. Thus, there were nine combinations: TT, TR, TS, RR, RT, RS, SS, ST, SR—the first letter indicates the fat fed in the grower, the second, in the finisher. Three animals per treatment group were slaughtered at 67.5, 80.0 and 92.5, together with three at 55 kg to provide a base-line. Samples of both inner and outer shoulder fat were taken at all slaughter weights and analysed for fatty acid content. The results demonstrated that fatty acid profiles of carcass fat reflected those of the dietary fat, with the inner layer tending to be more saturated. Thus, for example, the concentrations of linoleic acid (g/kg fat) in the outer layer of backfat changed from 225 to 201 (treatment RT), 171 to 206 (TR), 359 to 212 (ST) and 171 to 292 (TS) between 55 kg and final slaughter weight. Rate of change of fatty acid concentration with increasing slaughter weight following diet changeover at 55 kg was estimated from exponential functions. There were differences in the rate of change of individual fatty acid concentrations as influenced by the source of that fatty acid. Thus, for linoleic acid, the rate of change (estimated as the proportion of the concentration at a specific time compared with that of the asymptote) was 0.66, 0.88 and 0.95, respectively at 2, 4 and 6 weeks for RT compared with 0.61, 0.82 and 0.92 for ST. Generally, data demonstrated that the bulk of changes (between 0.6 and 0.7, expressed as a proportion of function asymptotes) occurred within approximately 14 days.