Nitrogen Metabolism, Tissue Carnosine Concentration and Blood Chemistry of Gravid Swine Fed Graded Levels of Histidine

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Abstract
Three nitrogen metabolism experiments were conducted to determine the qualitative and quantitative histidine need of first-litter gilts during the last third of pregnancy. A completely purified, crystalline L-amino acid diet was formulated to meet all nutrient needs of the gravid gilt when 2 kg/day were fed. Experiments 1 and 2 were 9-day nitrogen balance studies, each consisting of three littermate gilts subjected to three levels of dietary L-histidine in a Latin square arrangement of treatments. Nitrogen retention was depresed, but not significantly, when less than 0.12% histidine was fed. Complete deletion of histidine, however, did not depress retention below that observed when 0.06% was fed. This suggested that either histidine biosynthesis or its release from endogenous reserves was confounding retention data. Therefore in a third experiment, two gilts were fed a histidine-free diet for 24 days in an attempt to deplete endogenous reserves. For comparison, two siblings were fed 0.12% histidine during this same period. Nitrogen retention tended to be lower for gilts fed the histidine-free diet during each of three consecutive collection periods. Blood hemoglobin, muscle and olfactory bulb carnosine concentration, plasma protein and glutamic-oxaloacetic transaminase activity, and blood urea nitrogen were all unaffected by treatment. Offspring from gilts fed the histidine-free diet had lower blood hemoglobin concentrations than their counterparts from gilts receiving histidine. A tentative recommendation of 0.12% dietary L-histidine would seem justified for gravid swine.