Effects of long-term parenteral administration of vitamin B-6 on B-6 status and some aspects of the glucose and protein metabolism of early-weaned piglets

The present experiment aimed to determine the effect of feeding level and p arenteral supplements of vitamin B-6 (pyridoxine) on B-6 status as well as on glucose, C-peptide, insulin, alpha -amino-N and urea after a gastric bol us of glucose in weaned piglets; the plasma tryptophan, xanthurenic acid an d kynurenine responses to a gastric bolus of tryptophan were also measured. Forty-two piglets weaned at 2 weeks of age were distributed in seven block s of six animals each. Within each block, the animals were assigned to the following factorial treatments: two levels of feeding (28 (F28) and 56 (F56 ) g/kg(0.75) per d) administered by gastric-tube feeding and three levels o f parenteral (intramuscular injections) vitamin B-6 (0 (B(6)0), 15 (B(6)15) and 30 (B(6)30) mg/ d). In B(6)0 piglets, a decrease of 30 % and 20 % in e rythrocyte and plasma pyridoxal-5-phosphate respectively, were observed dur ing the 2 weeks post-weaning. In supplemented piglets, the erythrocyte pyri doxal-5-phosphate was maximised in B(6)15 piglets at a level 3-4 times high er than in B(6)0 piglets (P < 0.003). However, in plasma the maximal pyrido xal-5-phosphate concentration was reached in F28-B(6)30 piglets (P < 0.058) . The glucose and insulin responses to a gastric bolus of glucose were lowe r, and the post-bolus decrease of glucose was slower, in F28 than in F56 pi glets (P < 0.0001). The insulin:C-peptide ratio was 25 % greater in B(6)15 piglets (P < 0.082). After the bolus of glucose, the aminoacidaemia decreas ed differentially according to treatments (P < 0.047) while the uraemia was at least 2-fold higher (P < 0.001) in F28 piglets than in F56 piglets and tended to be maximised in B(6)30 piglets (P < 0.074). The response of plasm a tryptophan to the gastric bolus of tryptophan was 11 % lower in B(6)30 pi glets (P < 0.057). The plasma concentration of kynurenine increased continu ously during the post-bolus period and this response was more marked in F56 (P < 0.002) and in B(6)30 piglets (P < 0.02). Xanthurenic acid was undetec table in any of the treatments. The measurements on pyridoxine status sugge st that the present basal dietary level of B-6 (7.7 mg/kg) was not sufficie nt to cover the metabolic needs. For many criteria, an optimal level was re ached at 15 mg/d parenteral B-6 but the response of urea to glucose bolus s uggests that 30 mg/d was detrimental. Further studies are necessary to dete rmine the dietary level of B-6 equivalent to the present optimal parenteral supplements and its eventual effects on B-6 status and post-weaning growth performance of piglets.