Nitrogen metabolism, tissue carnosine concentration and blood chemistry of gravid swine fed graded levels of histidine.

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 8amino acid diet was formulated to meet all nutrient needs of the gravid gilt when 2 kg/day was 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.