Impairments in pyridoxine-dependent sulphur amino acid metabolism are highly sensitive to the degree of vitamin B6 deficiency and repletion in the pig

The objectives of the current study included the characterization of the temporal changes in indices of sulphur amino acid metabolism in piglets in response to vitamin B6 deficiency and repletion with graded levels of pyridoxine hydrochloride. In Experiment 1, 12 piglets (average initial weight = 5.3 kg; n = 6 per group) were fed a semi-purified diet containing either 0 (deficiency group) or 3 mg (control group) pyridoxine·HCl/kg diet, using a pair-feeding design, for 6 weeks. Piglets consuming vitamin B6-deficient diets exhibited decreased average daily gains on the 4th week and feed conversion efficiency from the 4th week until the end of the trial (P 25-fold increase in homocysteine; halving of cysteine values). At the end of Experiment 1, vitamin B6 deficiency significantly increased plasma methionine and serine levels, but decreased plasma glycine concentrations (P < 0.05). In Experiment 2, 20 pigs of 14 days old (initial BW = 5.0 kg) were subjected to a 4-week vitamin B6 depletion protocol, based on results obtained in Experiment 1. After the depletion period and assessment of baseline status (four pigs), remaining pigs were allocated to one of four dietary vitamin B6 repletion treatments: 0.75, 1.5, 2.25 and 3 mg/kg diet as pyridoxine·HCl (n = 4 per level) for 14 days. Significant dose-dependent increases in plasma PLP and cysteine, and decreases in homocysteine were observed, and these were sensitive to the duration of repletion. In conclusion, data from the current studies support the use of both plasma PLP and homocysteine as sensitive indices of vitamin B6 status in the pig. Additionally, the observed patterns of responses in vitamin B6-sensitive metabolites are supportive of an inclusion level of 2.25 mg/kg diet, as pyridoxine·HCl, in diets for young pigs