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

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© 1997 American Registry of Professional Animal Scientists. Seven experiments were conducted to evaluate the serum urea nitrogen (SUN) method of estimating the lysine requirement of 20-35-50-and 80-kg cross-bred barrows. Treatments within each experiment were replicated three times with four barrows per replicate (except Exp. 4, replicates 1 and 2 had three barrows per replicate; Exp. 6, replicates 1 and 2 had five barrows per replicate). Initial BW were 17.2 kg in Exp. 1; 35.2 and 37.0 kg in Exp. 2 and 3; 49.8 and 52.1 kg in Exp. 4 and 5; and 79.8 and 81.1 kg in Exp. 6 and 7. The lysine levels fed ranged from 0.35 to 1.25%, depending on the weight of the barrows. 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, the diets 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 barrows for initial SUN determination. Barrows 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 (linear, P<0.01; quadratic, P<0.02) for barrows in Exp. 1, 2, 3, and 7. Broken-line regression models were fitted to SUN data for each experiment to estimate lysine requirements. The two-slope model best described data from Exp. 5; the one-slope model best described data from all other experiments. Estimated lysine requirements were 1.04% for 20-kg barrows; 0.75 and 0.73% for the two experiments with 35-kg barrows; 0.79 and 0.81% for the two experiments with 50-kg barrows; and 0.76 and 0.83% for the two experiments with 80-kg barrows. 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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