Date Full Report Received09/29/2000
Date Abstract Report Received01/01/2000
National Pork Board website, Environmental Research Reports, Report # 98-004
Growing pigs were used to test whether decreasing dietary crude protein concentration could reduce nitrogen excretion, ammonia emission, volatile organic compounds (VOC) and odor, and to determine the gut endogenous contribution to these components. Another goal was to determine the amino acid digestibility as affected by dietary crude protein reduction. Six diets were fed in a latin square design. The diets consisted of 15, 12, 9 and 6% CP corn-soybean meal (CSBM) based diets, a 15% CP casein based diet and a protein-free diet. The protein-free diet and the casein diet were used to determine endogenous protein contribution to fecal nitrogen, ammonia, and VOC. The 12, 9 and 6% CP CSBM diets were obtained by diluting the 15% CP CSBM diet with cornstarch in order to maintain equal AA profile arising from intact protein sources, i.e., corn and soybean meal. In order to meet the amino acid requirements of the growing pig, diet formulation was based on the NRC (1998) ideal apparent amino acid digestibility pattern. Crystalline amino acids were added to the 12, 9 and 6% CP CSBM diets. Among them, glutamic acid was added to balance the essential amino acid (EAA) to non-essential amino acid (NEAA) ratio. Pigs were housed in metabolism cages to allow fecal and urinary collection. Reducing dietary crude protein resulted in a linear decrease in total nitrogen excretion (P<.05) and a quadratic decrease in urinary excretion (P < .05). This was accompanied by a reduction in ammonia emission (P < .05). Reduction of CP beyond 9% did not yield significant reduction in N excretion and ammonia emission, which were similar to that of pigs fed protein free diet. Thus, in pigs fed diets containing 9 and 6% CP, nitrogen excretion and ammonia emission were mainly of endogenous origin. Reducing crude protein and including amino acids improved nitrogen utilization linearly (P < .05) and amino acid digestibility (P < .05). Volatile fatty acids concentration from slurry increased with decreasing crude protein concentration (P < .05). The phenolic compounds were not detected to significant levels in any of the dietary treatment groups. The odor panel showed an increase in odor offensiveness as intact CP decreased. Comparing reduced intact CP diets to the 15% CP CSBM diet, only the 9 and 6% CP CSBM diets were found to be more offensive (P<0.05) with qualitative rankings of “moderately” offensive. The order of offensiveness (least to most) for the remaining treatments are as follows: protein-free, 12% CP CSBM , 15% CP casein, 2.70, 2.77, and 2.81, respectively, with qualitative rankings equivalent to “mild-moderately” offensive. In conclusion, reducing dietary crude protein to 9% was sufficient to minimize nitrogen excretion and ammonia emission while maintaining nitrogen retention similar to pigs fed a standard 15% corn-soybean meal based diet. However, the reduction in dietary crude protein was accompanied by an increase in volatile fatty acids and odor offensiveness.