136 Nitrogen retention was not different in pigs fed diets supplemented with 65 parts of DL-Methionine or 100 parts of MHA-Ca

An experiment was conducted to test the hypothesis that pigs fed a low crude protein diet supplemented on a product-to-product (wt-wt) basis with 65 parts of DL-methionine (DL-Met, 99%) or 100 parts of the calcium salt of the hydroxy analog of DL-Met (MHA-Ca, 84%) will not have different N retention. A mash Met-deficient basal diet [0.23% standardized ileal digestible (SID) Met and 0.55% SID Met + Cys], which was 19% below the requirement for 11 to 25 kg pigs was formulated. Four additional diets were prepared by supplementing the basal diet with 0.030 or 0.090% DL-Met, or 0.046 or 0.138% MHA-Ca. The greatest level of Met supplementation (0.64% SID Met + Cys) was close to the requirement. Thirty barrows (initial body weight: 16.37 ± 1.28 kg) were housed individually in metabolism crates and allotted to a randomized complete block design with 5 diets and 6 replicate pigs per diet. Feed was provided at 3.2 times the energy requirement for maintenance in 2 equal daily meals. Pigs had ad libitum access to water. After a 7-day adaptation period, fecal and urine samples were collected for 4 days to determine N balance. Data were analyzed using the MIXED procedure of SAS, and orthogonal-polynomial contrasts were used to determine linear effects of DL-Met and MHA-Ca levels and the effect of Met sources. Results indicated that pigs fed diets without supplementation of Met had reduced (P < 0.05) final BW, feed intake, and N intake compared with pigs fed diets supplemented with DL-Met or MHA-Ca, and no differences in final BW, feed intake, or N intake between pigs fed DL-Met or MHA-Ca were observed (Table 1). Fecal N increased (linear, P < 0.05) by supplementation of DL-Met to the diets, and urine N decreased (linear, P < 0.05) as MHA-Ca increased in the diet. Retention of N (g/day) increased (linear, P < 0.05) as DL-Met or MHA-Ca increased and N retention calculated as percent of intake increased (linear, P < 0.05) if MHA-Ca was added to the diet and tended to increase (linear, P < 0.10) if DL-Met was added to the diets. Retention of N calculated as percent of absorbed N also increased (linear, P ≤ 0.05) with increased Met in the diet regardless of source. However, retention of N measured as percent of intake was not different between DL-Met and MHA-Ca. In conclusion, pigs fed Met-deficient diets and supplemented with 65 parts of DL-Met or 100 parts of MHA-Ca on a product-to-product (wt/wt) basis did not have different N retention expressed as g per day, as percent of intake, or as percent of absorbed.