Studies on Reducing Nitrogen Excretion： I . Net Energy Requirement of Finishing Pigs Maximizing Performance and Carcass Quality Fed Low Crude Protein Diets Supplemented with Crystalline Amino Acids

摘要

Two experiments were conducted to investigate the effects of net energy (NE) level on the performance and carcass traits of finishing pigs fed low crude protein (CP) diets supplemented with crystalline amino acids (CAA). A total of 216 (Exp.1) and 360 (Exp.2) barrows (Yorkshire×Landrace×Duroc) were allotted to one of six treatments (n=6). The experimental diets were based on corn and soybean meal, and consisted of a highCP diet that contained approximately 16% CP and 2.50 Mcal/kg of NE as well as five lowCP diets in which the CP level of the diet was reduced by approximately four percentage units but was supplemented with crystalline lysine, methionine, threonine, and tryptophan. The low CP diets provided 2.64, 2.58, 2.50, 2.42, or 2.36 Mcal/kg in Exp.1 as well as 2.45, 2.40, 2.35, 2.30, or 2.25 Mcal/kg in Exp.2. In Exp.1, a linear (P=0.03) increase in weight gain was observed with decreasing NE level while the ratio of gain to feed was unaffected (P>0.05) by NE level. There was a linear increase (P=0.01) in the percentage of fatfree lean and a linear decrease (P=0.03) in the percentage of total fat with decreasing NE levels. In Exp.2, a significant quadratic (P=0.03) effect of NE level was observed for weight gain. The ratio of gain to feed demonstrated a significant (P<0.01) quadratic effect with pigs fed 2.35 and 2.40 Mcal/kg of NE. Pigs fed the diet containing 2.40 Mcal/kg of NE had the lowest percentage of total fat (36.95%) and the highest percentage of fatfree lean (49.36%). The overall results of these experiments indicate that feeding either a surplus or a deficiency of NE is detrimental to both pig performance and carcass composition when low CP diets supplemented with CAA are fed. Our results indicate that when the CP content of the diet is reduced by four percentage units and the diet is properly supplemented with CAA, maximum performance and carcass quality will be obtained if the diet provides approximately 2.42 Mcal/kg of NE.