Homocysteine remethylation in broilers fed surfeit choline or betaine and varying levels and sources of methionine from eight to twenty-two days of age

Experiments were conducted to assess the effect of surfeit choline (CHOL) or betaine (BET) on growth performance and homocysteine (HCY) remethylation of young broilers fed graded levels of DL-Met (DLM) or 2-hydroxy-4-(methylthio) butanoic acid (HMB). In Experiment 1, a corn-peanut meal diet deficient in Met (0.25% digestible) and Cys (0.28% digestible) was fed; treatments were formulated to contain graded levels (0, 0.04, or 0.08%) of Met from DLM or 0.04% HMB (adjusted for 88% purity) that were fed in the presence or absence of surfeit isomethyl CHOL (0.25%) or BET (0.28%). In Experiment 2, identical treatments were used, but an additional level of HMB (0.08%) was fed, and the basal diet was adequate in Cys (0.43% digestible). There was no overall effect of CHOL or BET on growth performance in Experiments 1 and 2 (P > 0.05); a significant improvement (P < 0.05) in weight gain and feed efficiency did occur with CHOL and BET addition to the basal diet in Experiment 2. In both experiments, weight gain increased linearly (P < 0.05) with the addition of DLM or HMB. Slope ratio methodology was used to assess HMB efficacy in Experiment 2. In the presence of adequate Cys, HMB efficacy was 81.3%; addition of surfeit BET or CHOL had minimal effect on efficacy. The stable isotope study revealed that CHOL and BET addition to diets deficient in Met and Cys or Met alone increased HCY remethylation. It also showed that CHOL and BET have greater influence on folate-dependent remethylation of HCY (via Met synthase) than on BET-dependent remethylation (via BET-HCY methyltransferase) and that levels of CHOL and BET and type of S amino acid deficiency effect remethylation and HMB efficacy.