The Use of Serum Urea Nitrogen Concentrations for the Determination of Lysine Requirements of Gilts

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© 1997 American Registry of Professional Animal Scientists. Five experiments were conducted to evaluate the serum urea nitrogen (SUN) method of estimating the lysine requirement of 20, 35, 50, and 80 kg crossbred gilts. In Exp. 1 and 2, 75 gilts were allotted to five treatments with three replicates of five gilts per replicate. Average initial BW were 17.7 and 34.2 kg for Exp. 1 and 2, respectively. In Exp. 3, 4 and 5, 80 gilts were allotted to five treatments with four replicates and four gilts per replicate with average initial BW of 48.5, 53.1, and 77.4 kg, respectively. The lysine levels fed were the following: Exp. 1 (0.65, 0.80, 0.95, 1.10, 1.25%); Exp. 2 (0.57, 0.72, 0.87, 1.02, 1.17%); Exp. 3 (0.56, 0.66, 0.76, 0.86, 0.96%); Exp. 4 (0.58, 0.73, 0.88, 1.03, 1.18%); and Exp. 5 (0.33, 0.53, 0.73, 0.93, 1.13%). Within an experiment, all treatment diets contained the concentration of corn and soybean meal of the diet with the lowest level of lysine. With the exception of lysine, they met or exceeded the ideal amino acid pattern for all indispensable amino acids for the diet containing the highest level of lysine. All treatment diets were isonitrogenous and equal in electrolyte balance (Na+K-Cl). An initial blood sample was taken from all gilts for initial SUN determination. Gilts were fed treatment diets for a minimum of 6 d before blood samples were collected for final SUN determination. All experiments were randomized complete block designs and initial SUN was used as a covariate for final SUN. As dietary lysine increased, final SUN decreased quadratically for gilts in Exp. 1 (P<0.01), Exp. 4 (P<0.04), and Exp. 5 (P<0.01). For gilts in Exp. 2 and 3, there was a decrease (linear, P<0.01) in final SUN, as dietary lysine level increased. One-slope, broken-line regression models estimated lysine requirements of 1.13, 1.11, 0.80, 0.77, and 0.64% for 20, 35, 50, 50, and 80 kg gilts, respectively. The SUN method can be used to obtain lysine requirement estimates for pigs at a specific BW.

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Professional Animal Scientist

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