The relative effectiveness of 2-hydroxy-4-(methylthio) butanoic acid and DL-methionine in young swine

We compared the effectiveness of 2-hydroxy-4-(methylthio) butanoic acid (HMB) and DL-methionine (DLM) as sources of L-methionine activity in methionine-deficient primary cultures of pig liver cells and methionine-deficient early-weaned pigs. Viable hepatocytes were obtained from minced pig liver and maintained in a high density, differen- tiated, nonproliferation cell culture system. Culture medium was supplemented with HMB, DLM, or L- methionine, and cells were pulse-dosed with L- ( 14 C(U))leucine for 24 h to determine the level of protein synthesis. Leucine incorporation per milligram of protein indicated a six-to eightfold increase in protein synthesis ( P < .01) with methionine levels between 5 and 10 mM, regardless of source of methionine activity. Two 24-pen replicate methionine dose titrations were conducted with 95 early-weaned commercial crossbred pigs. The pelleted corn, dried whey, and porcine plasma basal diet contained 1.5% lysine, .23% methionine, and .48% cystine and was supplemented with 0, .05, or .10% methionine activity as DLM or HMB for 21 d. There was a 134, 104, and 61% increase ( P < .01) in cumulative ADG for each successive week on study with a 30 and 19% improvement in feed/gain ( P < .01) after 7 and 14 d. Performance responses due to source of methionine activity did not differ and slope ratio potency determi- nations (gain vs intake of methionine source) of HMB vs DLM indicated a 119, 111, and 95% relative activity for cumulative weekly performance. These results support the hypothesis that HMB and DLM provide equimolar levels of methionine activity in swine.