Effects on growth rate and utilisation of amino acids in weaner pigs fed diets containing whole proteins and free amino acids in combination with different energy sources

Abstract

This experiment was designed to determine the effects of 3 protein and 3 energy (carbohydrate) sources on the growth rate of weaner piglets and their eciency of nutrient utilisation. All 3 energy sources and 2 of the protein sources [casein plus free amino acids (casein), free amino acids alone (FAA)] were chosen because they were suitable for studies measuring amino acid utilisation. The third protein source, based predominantly on peptide protein, was a combination casein-fish meal-soyabean meal (CFS). The combinations of carbohydrates tested were sucrose alone, sucrose plus 150 g lactose/kg, and wheat starch plus 150 g sucrose plus 150 g lactose/kg. The experiment was a randomised complete block design based on a 33 factorial arrangement with 5 blocks and 9 pigs per block. Piglets given CFS as the protein source exhibited greater (P < 0·001) weight gain than those consuming casein or FAA (494 v. 415 and 345 g/day) and deposited protein more eciently (P < 0·001) (e.g. crude protein retention/ileal-digestible protein intake, 0·65 v. 0·56 and 0·49). The apparent digestibility of nitrogen (N) and amino acids was lower for the CFS-fed piglets (0·83 and 0·88) than for those given casein (0·92 and 0·95) or FAA (0·94 and 0·96). The daily weight gains of piglets given diets containing starch, sucrose, and lactose were 9-10% lower (P < 0·05) than those consuming either sucrose or sucrose plus lactose (391 v. 433 and 430 g/day). The energy sources, however, had no effect on ileal digestibility of amino acids or empty body composition. Neither casein nor FAA diets were found to be acceptable sources of amino acids for studies on amino acid utilisation. Sucrose and sucrose plus lactose were excellent energy sources for piglets. In contrast, wheat starch was found to be unsuitable for inclusion in synthetic weaner diets for piglets with a liveweight of 5-20 kg.