The Use of Low Protein Liquid Diets to Determine the Methionine Requirement and the Efficacy of Methionine Hydroxy Analogue for the Three-Week-Old Pig

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Abstract
A mechanical feeding device that dispenses liquid diets hourly was developed to feed 3-week-old pigs under carefully controlled and sanitary conditions. Pigs were weaned at 19–21 days of age, placed in individual cages of the automatic feeder, and trained to eat low protein (9%) milk diets, which were supplemented with essential amino acids, glutamic acid and monosodium glutamate so as to be equivalent to 14% protein nitrogen. The basal 9% protein diet contained 0.25% L-methionine and 0.08% L-cysteine and was supplemented with L- or DL-methionine or DL-methionine hydroxy analogue (MHA) at various levels for evaluation of the methionine requirement. Pigs fed the basal diet showed a significant decrease in gain, feed efficiency and plasma urea (P < 0.05) relative to animals that received supplemental methionine or MHA. The plasma methionine concentration remained below 0.2 µmol/ml plasma when pigs were fed diets containing 0.25–0.51% methionine; however, a significant increase in plasma methionine (P < 0.05) was seen when pigs were fed diets that contained greater than 0.51% methionine activity in the form of L- or DL-methionine or DL-MHA. The highest average daily gain (470 g) obtained with a diet containing 0.51% methionine was significantly better (P < 0.05) than diets containing more or less L- or DL-methionine, and the feed efficiency of this diet (1.58 kg feed per kilogram gain) was also significantly better (P < 0.05) than the feed efficiency obtained with other dietary methionine levels. MHA (0.17%) added to the basal diet significantly improved the average daily gain (P < 0.05) and lead to a significant decrease in plasma urea (P < 0.05) relative to pigs that received the basal diet. Supplemental MHA (>0.51% methionine level) produced significant increases (P < 0.05) in plasma methionine. These data show that the methionine requirement of the 3-week-old pig can be satisfied with L- or DL-methionine or DL-MHA at a level equal to 0.51% of the dietary solids and that these three are equivalent. These experiments also show that low protein diets supplemented with amino acids can be used for liquid feeding of pigs weaned at 3 weeks of age, and average daily gains of greater than 400 g can be realized.