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The Determination of the Amino Acid Requirements of Pigs in the Nursery Phase
An experiment using 202 total pigs, assigned to one of 4 diets was conducted to determine the essential amino acid requirements of nursery pigs. Except for lysine, diets met or exceeded 1998 NRC. Treatment 1 was slightly deficient in lysine relative to the 1998 NRC (1.40, 1.23, and 1.10% of total dietary lysine in phases I, II, and III, respectively). Treatment 2 was equivalent to the 1998 NRC recommendations (1.50, 1.33, and 1.20% of total dietary lysine in phases I, II, and III, respectively). Treatment 3 was intermediate between the 1998 recommendations and the newly revised 2012 publication (1.60, 1.43, and 1.30% of total dietary lysine in phases I, II, and III, respectively). Treatment 4 was equivalent to the 2012 NRC publication (1.70, 1.53, and 1.40% of total dietary lysine in phases I, II, and III, respectively). Crystalline amino acids (LYS, THR, MET) were used to maintain an ideal amino acid pattern (1.00, .62, .57 respectively) across treatments. Treatments were fed over 3 phases: Phase I, D0-7; Phase II, D7-21; and Phase III, D21-35. There were no significant differences (P >.10) in growth rate or feed intake, but feed efficiency improved linearly (P < .05) as amino acid content increased (Gain:Feed of 0.66, 0.69, 0.70, and 0.72 in treatments 1,2,3, and 4, respectively). Blood samples were obtained from pigs at the end of each dietary phase (D7, 21, and 35) for determination of plasma urea concentration. There was a significant linear response to diet on days 7, 21, and 35 (P<0.05), with a significant quadratic response on days 21 and 35 (P<0.001). This suggests that nitrogen excretion is reduced in pigs fed higher levels of crystalline amino acids, which could potentially reduce environmental impact. In contrast to the positive linear correlation between dietary lysine levels and feed efficiency, the blood urea response indicated that the requirement for amino acids was met at 1.33% total lysine diets in Phase II, and 1.20% lysine in Phase III; these results most closely correspond to the 1998 NRC guidelines. These results suggest that the decision whether to feed the higher levels of amino acids in the nursery depends on the added cost associated with those diets. Based on growth rate and feed intake, there is no evidence that the higher dietary levels are needed. However, feed efficiency and plasma urea response indicate that the higher levels may be justified.
Keywords: Lysine, Nursery, pigs