The effect of dietary methionine and its relationship to lysine on growth performance of the segregated early-weaned pig.

Two experiments were conducted to determine the dietary methionine requirement and the appropriate methionine:lysine for the segregated early weaned-weaned pig. In Exp. 1, 435 crossbred pigs (9.5 +/- 4 d of age and 3.5 kg BW) were fed diets (1.8% lysine, .62% cystine) containing 10% spray-dried plasma protein (SDPP) and 1.75% spray-dried blood meal (SDBM) from day 0 to 21 postweaning. Pigs were feed one of six dietary treatments from .36% to .56% total dietary methionine (.317 to .517% apparent digestible methionine). From d 0 to 7 and d 0 to 21 postweaning, ADG and gain:feed ratio (G/F) increased (linear, P < .01, P < .05, respectively) as dietary methionine increased. In Exp. 2, 350 crossbred pigs (9.0 +/- 2 d of age and 3.8 kg BW) were used to determine the appropriate methionine:lysine ratio for the segregated early-weaned pig in a 2 x 5 factorial arrangement. Two lysine levels (1.8 and 1.4%) and five methionine levels within each lysine level were used to obtain methionine:lysine ratios ranging from 21.5 to 33.5%. From d 0 to 21 postweaning, pigs were assigned to one of 10 dietary treatments containing 25% dried whey, 12% lactose, 7.5% SDPP, 6.0% select menhaden fish meal, and 1.75% SDBM. No methionine x lysine interactions were observed (P > .10). From d 0 to 7 postweaning, increasing dietary methionine improved (quadratic, P < .01) ADG and ADFI regardless of dietary lysine. From d 0 to 14 postweaning, increasing dietary methionine improved ADG (quadratic, P < .01), ADFI quadratic, P =.02), and G/F (quadratic, P < .10). Inflection point analysis projected maximum ADG at methionine:lysine ratios of 27 and 27.5% for pigs fed 1.4 and 1.8% lysine, respectively. Cumulative (d 0 to 21 postweaning) ADG, ADFI, and G/F were improved (quadratic, P < .05) by increasing dietary methionine. Increasing dietary lysine improved (P < .01) ADG and G/F from d 0 to 7, from d 0 to 14, and for the overall experiment. In conclusion, a diet with 1.8% total lysine that includes spray-dried blood products must contain .48 to .52% total dietary methionine (.437 to .477% apparent digestible) or 27.5% of total lysine to maximize growth performance of pigs from d 0 to 21 postweaning (3.5 to 12 kg BW).