Bioavailability Of The Dl-Methionine And The Calcium Salt Of Dl-Methionine Hydroxy Analog Compared With L-Methionine For Nitrogen Retention In Starter Pigs

Two nitrogen balance studies were conducted to evaluate the relative bioavailability values (RBV) of DL-methionine (DL-Met) and DL-methionine hydroxy analog calcium salt (MHA-Ca) to L-methionine (L-Met) as Met sources fed to pigs. In experiment 1, 42 pigs were assigned to 7 treatments feeding with basal diet (BD) formulated to be deficient in Met (0.22% standardized ileal digestible basis) but adequate in other amino acids. Diets included (1) BD, (2) BD + 0.025% DL-Met, (3) BD + 0.050% DL-Met, (4) BD + 0.075% DL-Met, (5) BD + 0.025% L-Met, (6) BD + 0.050% L-Met, and (7) BD + 0.075% L-Met. Increasing levels of L-Met and DL-Met enhanced N retained (g/d) and N retention (% of intake) linearly (P < 0.01). Using a linear slope ratio procedure, a product-to-product RBV of DL-Met compared with L-Met was 94% (95% confidence limits: 65% to 123%) based on N retained expressed as g/d and 99% (95% confidence limits: 70% to 128%) for N retention expressed as % of intake. In experiment 2, 42 pigs were allotted to 7 treatments in another N-balance trial. Diets included (1) BD, (2) BD + 0.025% L-Met, (3) BD + 0.050% L-Met, (4) BD + 0.075% L-Met, (5) BD + 0.030% MHA-Ca, (6) BD + 0.060% MHA-Ca, and (7) BD + 0.089% MHA-Ca. An increase in dietary inclusion rates of L-Met increased (P < 0.01) N retained (g/d) linearly while increasing levels of MHA-Ca had no effects (P > 0.05) on N retained (g/d) and N retention (% of intake). Using linear slope-ratio regression, the RBV of MHA-Ca compared with L-Met was 70% (95% confidence limits: 59% to 81%) on a product-to-product basis or 83% on equimolar basis based on N retained expressed as g/d. Overall, the mean RBV of DL-Met to L-Met of 97% (95% confidence limits cover 100%) indicated that DL-Met and L-Met are equally bioavailable as Met sources in pigs. Compared with L-Met, the RBV of MHA-Ca was lower at 70% (95% confidence limits: 59% to 81%) on a product-to-product basis or 83% on equimolar basis in starter pigs.