Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2002
Publication Date: 3/20/2002
Citation: Parr, T.M., Kerr, B.J., Baker, D.H. 2002. Plasma urea nitrogen as an indicator of the isoleucine requirement of grower pigs. Journal of Animal Science. 80(2):72. Interpretive Summary: There are only limited empirical estimates of the isoleucine requirement for growing-finishing pigs as estimated in the National Research Council Subcommittee on Swine Nutrition, 1998. As environmental issues with nitrogen losses from swine operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding amino acid limitations in low crude protein diets and their desired concentration in feeding programs for optimal production and minimal nitrogen excretion, is paramount. Results from two experiments show that utilization of red blood cells in swine diets clearly creates an isoleucine deficient diet, and show that supplementation of crystalline isoleucine alleviates these depressions in growth, feed intake and feed efficiency to a level similar to pigs fed standard diets. Requirement data suggests that the true digestible isoleucine requirement of grower pigs appears to be in the range of 0.44 to 0.47%, which is in close agreement with the National Research Council Subcommittee on Swine Nutrition (1998) estimate of 0.45%. Research results described in this report provides nutritionists at universities, feed companies, and swine production units vital data on empirical research methodology on how to clearly define the isoleucine needs of growing-finishing swine to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Technical Abstract: Two trials were undertaken to verify the isoleucine (Ile) requirement of growing (25 to 45 kg) pigs. A previous growth trial in our laboratory had suggested a true digestible Ile requirement of between 0.44 and 0.47% of the diet. In the first study, a replicated 5 x 5 Latin Square design was used to determine the Ile requirement. Five barrows (square one) and five gilts (square two) were fed corn-red blood cell diets containing five graded increments of L-Ile to accomplish true digestible Ile levels of 0.35%, 0.39%, 0.43%, 0.47% and 0.51%. Pigs received each test diet for a period of 4 d, with blood being drawn at 0900 on the 5th d. Samples were analyzed for plasma urea nitrogen (PUN). Barrows had higher (P < 0.01) PUN values than gilts and PUN decreased linearly (P < 0.01) in both sexes as Ile was incremented. The data suggested, however, an apparent plateau in both sexes at 0.47% digestible Ile. In the second trial, 100 pigs were assigned one of five diets formulated to test the pigs' response to Ile in the presence and absence of excess leucine (Leu) and valine (Val). The basal diet contained 0.38% true digestible Ile, with Leu and Val formulated to be just above the requirement at 0.97 and 0.63%, respectively. Treatments were: 1) corn-soybean meal positive control, 2) Ile-deficient basal, 3) as 2 + 0.10% L-Ile, 4) as 2 + 1.0% L-Leu and 0.50% L-Val, and 5) as 2 + 0.10% L-Ile + 1.0% Leu + 0.50% L-Val. Pigs (26.0 kg initial body weight) were fed the experimental diets for 20 d, after which all pigs were bled for PUN assessment. Whether Ile-deficient (diets 2 and 4) or adequate (diets 3 and 5), excess Leu and Val depressed (P < 0.03) both feed intake and weight gain, and tended to increase PUN. This suggested that excess Leu and Val may antagonize Ile when diets contain minimal levels of Ile. In conclusion, the true digestible Ile requirement of grower pigs appears to be in the range of 0.44 to 0.47%, which is in close agreement with the NRC (1998) estimate of 0.45%.