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Nitrogen Metabolism of Gravid Gilts Fed Purified Diets Deficient in Either Leucine or Tryptophan

University of Illinois, Urbana 610801²

Abstract

Three nitrogen metabolism assays using first-litter, crossbred gilts averaging 80 days postcoitum were conducted to evaluate the quantitative leucine and tryptophan requirements of the gravid gilt. Each assay consisted of three dietary treatments fed at 2.0 kg per day in three consecutive 9-day periods (4-day pretest, 5-day quantitative urine collection). Completely purified diets (12.8% protein equivalent) were formulated with crystalline L-amino acids included at the known minimum levels needed for pregnancy in swine. Nitrogen for dispensable amino acid biosynthesis was provided by a mixture of glutamic acid and glycine. In assay 1, reduction of leucine from .58 to.34% of the diet did not depress nitrogen retention, however, retention was depressed in a subsequent assay when levels less than .34% were fed. In assay 3, complete deletion of tryptophan resulted in absolute diet refusal within 4 days in two of three gilts observed. Nitrogen retention was reduced by feeding .03% tryptophan compared with .07%, the N.R.C. requirement. Negative nitrogen balance (–1.6 g/day) was obtained for the single gilt consuming a tryptophan-free diet. Plasma urea nitrogen tended to be elevated when deficient levels of tryptophan were fed. Thus, feeding less than .34% available leucine (6.8 g/day) or .07% available tryptophan (1.4 g/day) to gravid gilts during the last one-third of gestation appears unwarranted at this time.

¹ Part of a thesis submitted to the Graduate College of the University of Illinois in partial fulfillment of the requirements for the Ph.D. degree in Animal Science.

² Animal Science Department.