PTEROYLGLUTAMIC (FOLIC) ACID IN DIFFERENT FEEDSTUFFS - THE PTEROYLGLUTAMATE CONTENT AND AN ATTEMPT TO MEASURE THE BIOAVAILABILITY IN PIGS

Sixty piglets selected after weaning at 4 weeks of age were assigned t o five replicates of twelve animals each. In each of these replicates the postprandial variations in serum pteroylglutamate after the ingest ion of twelve sources of dietary pteroylglutamic acid were recorded tw ice weekly at 10 and 16 weeks of age. In six of these sources of ptero ylglutamic acid the chemically pure form of the vitamin was incorporat ed into a semi-purified diet at concentrations varying between 0 and 1 .0 mg/kg. The six other sources were provided by a soya-bean meal, rap eseed meal, maize, barley, wheat, and a commercial vitamin premix. The concentrations of pteroylglutamates measured by radioimmunoassay in t he different feedstuffs were, in most cases, far from the values repor ted in the literature, except for maize. Indeed, while total pteroylgl utamates in barley, wheat and rapeseed meal were lower by 35-56%, 17-5 0% and 60% respectively compared,vith references values, the correspon ding values for soya-bean meal ranged from one third to twice as much. The area under the curve (AUG) of the pre- and postprandial (1, 2, 3, 5 and 7 h) serum pteroylglutamate following ingestion of increasing l evels of chemically pure pteroylmonoglutamic acid was used to derive a regression for the 100% bioavailability of dietary pteroylglutamic ac id. The corresponding AUC for the feedstuff sources of pteroylglutamat es were used in the regression to determine the proportion of bioavail able pteroylglutamates out of total pteroylglutamates measured in thes e ingredients. No relationship (P > 0.66) was found between the level of chemically pure dietary pteroylmonoglutamic acid and the postprandi al AUC. In fact, there was no significant (P > 0.11) increase in the p ostprandial concentration of serum pteroylglutamate for any of the pte roylglutamate sources used except for wheat. Moreover, values tended ( P < 0.08) to be lower at 5 and 7 h postfeeding except for wheat and ba rley. It was hypothesized that this decrease is probably linked to the postfeeding variation in bile secretion which drains considerable amo unts of circulatory pteroylglutamates. The results of the present expe riment indicate that further research on analytical procedure is neede d in order to provide a reliable method for measuring concentrations o f pteroylglutamic acid in different sources of a given feedstuff used in pig feeding. In addition to this analytical concern, the measuremen t of the proportion of bioavailable pteroylglutamic acid in feedstuffs for pigs using postprandial variations of serum pteroylglutamates app ears to be technically hazardous.