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Aromatic Amino Acid Requirement of the Lactating Sow¹

Iowa Agricultural and Home Economics Experiment Station, Ames 50011

Abstract

Six mature Yorkshire x Landrace sows were randomly assigned to a 6 x 6 Latin-square experiment on d 5 of lactation to determine the total phenylalanine (Phe) and tyrosine (Tyr) requirement. A control diet of corn sugar, cornstarch, whey, L-glutamic acid, solka floc, soybean oil, amino acids, minerals and vitamins was supplemented with L-Phe to provide .30 (basal), .45, .60, .75, .90 and 1.05% total aromatic amino acids (TAAA). Each diet was fed to a maximum of 5.5 kg/d within each of six 10-d periods. Feed intake, average pig weight gain and sow milk yield decreased linearly (P<.01) with increasing period. Sow milk yield was maximized at .75% TAAA (quadratic, P<.10), but average pig weight gain did not reflect the higher yield. Urea nitrogen decreased quadratically with increasing dietary Phe in both plasma (P<.05) and urine (P<.01) to a breakpoint at .56% TAAA. Plasma Phe increased (quadratic, P<.01) as dietary TAAA increased, but no clear inflection point was obtained. A sharp rise (quadratic, P<.001) in plasma Tyr occurred at .73% dietary TAAA. Plasma lysine decreased (linear, P<.001) to a low level at .76% TAAA, but plasma methionine was unaffected by treatment. Urine allantoin/urea x protein intake was maximized at .61% TAAA (quadratic, P<.01). Nitrogen (N) intake varied among diets (quartic, P<.05), but fecal N was not altered by TAAA level. Urine N decreased quadratically (P<.01) with increasing Phe, yielding maximum (P<.01) percentage N retention (excluding milk N) at .58% TAAA. Because daily milk N secretion also increased (linear, P<.01) with dietary TAAA, there were no treatment differences in overall N balance (including milk N). If equal weight is given to all response criteria, .65% TAAA seems to meet the dietary requirement for the lactating sow. In a diet containing natural ingredients, the requirement would increase to .75% of the diet, or 41.2 g/d for sows fed 5.5 kg/d.

¹ Journal Paper No. J-11805 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 2357.

² Dept. of Anim. Sci.