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 dietary nitrogen on the growth performance and carcass traits of crossbred (Landrace X Hampshire X Duroc) finisher pigs. In Experiment 1, 15 pens containing gilts and castrated males (six pigs per pen) averaging 53.7 +/- 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 were 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 included as part of dietary treatments. Two hydrolyzed feather meal (FM) diets 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 lysine or 132 g CP kg(-1) to the Iso-Lys and Iso-N diets, respectively, and additional lysine and CP were supplied by FM, A fundamental assumption 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 rate of protein accretion, but it would reduce the rate of fat accretion, thus improving leanness of pigs. Pigs were housed and fed individually 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 slaughtered. 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 high, but this depression was not observed in pigs fed the Iso-Lys diets (Iso-Lys vs. Iso-N, P = 0.06). Pigs fed the High diets had lower carcass 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 in the diets (Iso-Lys or Iso-N). The results indicate that providing extra dietary nitrogen may be a viable method to enhance leanness of finisher pigs, even though a possible increase in urinary N excretion is a potential environmental concern. In addition, the low quality protein sources for pigs such as FM may be used effectively as a source of extra dietary nitrogen to enhance leanness of finisher pigs.