SUPPLEMENTAL FAT AS AN ENERGY SOURCE IN THE DIETS OF SWINE AND RATS: II. ENERGY AND NITROGEN DIGESTIBILITY, NITROGEN RETENTION AND CARCASS FAT COMPOSITION

Abstract

Apparent energy and nitrogen digestibility and nitrogen retention of diets containing 0, 15 or 30 per cent supplemental stabilized tallow and 14, 18 or 22 per cent protein were determined with pigs at average weights of 7 and 45 kilograms and with 4- to 5-week-old weanling rats. Fat levels in the diets did not influence apparent digestible energy coefficients or nitrogen retention. Apparent nitrogen digestibility was increased when supplemental fat was added to rat diets but was not significantly influenced by fat levels in pig rations. Increased protein levels decreased energy digestibility in rats, but improved nitrogen digestibility in 45-kilogram pigs and nitrogen retention in 7-kilogram pigs. In 45-kilogram pigs, nitrogen retention decreased as protein levels of the rations increased.The degree of unsaturation, as measured by Iodine Absorption Number, was greater for backfat than for leaflard. The unsaturation of the carcass fat was increased when pigs were fed supplemental fat but the increase was not uniform between rations varying in protein level. Saponification Number of the backfat and leaflard in pigs was not influenced by fat levels in the diet but was increased by increasing protein levels.