Growth performance, blood parameters and metabolic-enzyme gene expression of finishing pigs as affected by dietary level of methionine + cystine supplemented with vitamin B6

Abstract

Context Methionine (Met) is an essential amino acid in pig diets. However, high blood homocysteine concentration, a risk factor for cardiovascular disease, can arise from high dietary Met intake and may indicate an imbalance in the Met cycle. Vitamin B6 acts as a cofactor for enzymes associated with the trans-sulfuration pathway, considered the major elimination route of excess homocysteine. Aims We evaluated the effects of different levels of dietary Met and vitamin B6 supplementation and their interaction with respect to growth performance, blood parameters and metabolic-enzyme gene expression of finishing pigs. Methods Fifty-six crossbred barrows, averaging 75.11 ± 1.84 kg bodyweight (BW), were assigned in a completely randomised block design arranged in a 2 × 4 factorial with two levels of vitamin B6 supplementation (1.58 and 3.58 mg/kg) and four levels of standardised ileal digestible (SID) Met + cystine (Cys) (0.35%, 0.45%, 0.55 and 0.65%), with seven replicates and one animal per pen, for an average duration of 26 days. BW of each pig and quantity of experimental diets on-offer and consumed were recorded at the beginning and end of the experiment. Plasma concentrations of glucose, urea, total proteins, creatinine and triacylglycerol were determined by the colourimetric method, and serum homocysteine by chemiluminescence. Gene expression was measured by quantitative real-time polymerase chain reaction. Key results No interactions (P > 0.05) between vitamin B6 supplementation and SID Met + Cys levels were observed for growth performance, blood parameters or metabolic-enzyme gene expression. Higher vitamin B6 supplementation (3.58 mg/kg) improved (P = 0.05) the feed : growth ratio. Treatments did not affect (P > 0.05) expression of the enzymes methionine synthase or cystathionine γ-lyase, and there was a linear increase (P = 0.01) in serum homocysteine levels with increasing dietary Met + Cys. Increasing vitamin B6 supplementation (3.58 mg/kg) in finishing pig diets increased plasma glucose concentration (P = 0.05), but did not mitigate the increase in homocysteine concentration. Conclusions Overall, a dietary SID Met + Cys intake of 10.46 g/day (corresponding to 0.35%) was sufficient for the growth of finishing barrows from 75 to 100 kg BW. Vitamin B6 supplementation at 3.58 mg/kg improved the feed : growth ratio but was not effective for metabolising the increasing homocysteine concentration via the trans-sulfuration pathway. Implications This study provides much needed empirical data on the dietary SID Met + Cys requirements for finishing pigs, and the metabolism of these amino acids.