EFFECTS OF HYDROLYZED FEATHER MEAL AS A SOURCE OF EXTRA DIETARY NITROGEN ON GROWTH-PERFORMANCE AND CARCASS TRAITS OF FINISHER PIGS

Two experiments were conducted to investigate the effects of extra die tary nitrogen on the growth performance and carcass traits of crossbre d (Landrace X Hampshire X Duroc) finisher pigs. In Experiment 1, 15 pe ns containing gilts and castrated males (six pigs per pen) averaging 5 3.7 +/- 1.9 kg were randomly assigned to five soybean meal (SBM) diets calculated to contain 4.8-9.8 lysine kg(-1) in each of two trials. In Experiment 2, 21 gilts and 21 castrated males averaging 57.1 +/- 4.5 kg were randomly assigned within sex to seven diets. Two SBM diets wer e formulated to contain 7.3 g lysine and 150 g crude protein (CP) kg(- 1) (Med) or 8.5 glysine and 167 g CP kg(-1) (High). An additional SBM diet containing 6.0 g lysine and 132 g CP kg(-1) (Low) was also includ ed as part of dietary treatments. Two hydrolyzed feather meal (FM) die ts were formulated to be iso-lysinic (Iso-Lys) to the Med and High SBM diets. Two additional FM diets were formulated to be iso-nitrogenous (Iso-N) to the Med and High SBM diets. Corn and SBM provided 6.0 g lys ine or 132 g CP kg(-1) to the Iso-Lys and Iso-N diets, respectively, a nd additional lysine and CP were supplied by FM, A fundamental assumpt ion of the design for Experiment 2 was that providing extra lysine and (or) CP (i.e. above the optimum level) would have no effect on the rat e of protein accretion, but it would reduce the rate of fat accretion, thus improving leanness of pigs. Pigs were housed and fed individuall y in Experiment 2, and allowed ad libitum access to feed and water in both experiments. At the average weights of 101.3 +/- 2.0 kg and 108.5 +/- 5.5 kg for Experiment 1 and 2, respectively, pigs were slaughtere d. In Experiment 1, pigs responded to an increase in dietary lysine up to 7.3 g kg(-1) (analyzed to be 8.5 g kg(-1)), and there seemed to be little or no improvement in the growth performance or carcass traits with further increases. In Experiment 2, weight gain of pigs decreased (P < 0.05) as dietary lysine and CP levels increased from medium to h igh, but this depression was not observed in pigs fed the Iso-Lys diet s (Iso-Lys vs. Iso-N, P = 0.06). Pigs fed the High diets had lower car cass backfat (P < 0.05), larger longissimus muscle area (P = 0.08) and higher specific gravity (P < 0.05) and proportion of lean (P < 0.05) than those fed the Med diets. The improved carcass quality in response to the increased dietary lysine and CP levels from medium to high was independent of the source (SBM or FM) or method of incorporating FM i n the diets (Iso-Lys or Iso-N). The results indicate that providing ex tra dietary nitrogen may be a viable method to enhance leanness of fin isher pigs, even though a possible increase in urinary N excretion is a potential environmental concern. In addition, the low quality protei n sources for pigs such as FM may be used effectively as a source of e xtra dietary nitrogen to enhance leanness of finisher pigs.