The relative bioavailability (RBV) of a dipeptide DL-methionyl-DL-methionine (DL-Met-Met) was compared with DL-methionine (DL-Met) in growing pigs (experiment 1; N-balance study) and in weaned pigs (experiment 2; performance study). In experiment 1, 42 barrows with an initial body weight (BW) of 21.0 ± 1.37 kg were assigned to 7 dietary treatments with 6 replicate/pigs per treatment in a nitrogen (N) balance study to evaluate the RBV of DL-Met-Met to DL-Met. A basal diet (BD) was formulated to be adequate for all amino acids with the exception of Met + Cys which was 68% of the requirement [4.7 g/kg standardized ileal digestible (SID) Met + Cys; 11.5 g/kg SID Lys] for 20-25 kg pigs. Three graded levels of DL-Met (0.3, 0.6 and 0.9 g/kg) and DL-Met-Met (0.306, 0.612 and 0.919 g/kg) were supplemented to the BD to create diets 2-7. In experiment 2, a total of 189 weaned pigs (initial BW of 10.2 ± 0.98 kg) were assigned to 7 dietary treatments with 9 replicates/pens of 3 pigs per treatment. The dietary treatments consisted of a Met-deficient BD (5.3 g/kg SID Met + Cys; 13.0 g/kg SID Lys) and the same 3 graded levels of DL-Met and DL-Met-Met as in Exp. 1. In experiment 1, supplementation with DL-Met or DL-Met-Met linearly decreased (P ≤ 0.01; linear) urinary N excretion and increased (P ≤ 0.02; linear) N retained (g/day), N retention (% of intake and % of absorbed). However, there was no effect of Met sources on all N balance parameters. Based on the slope-ratio regression the RBV for DL-Met-Met compared to DL-Met was estimated 111% [95% confidence interval (CI): 63-158%] for N retained (g/d), 109% (95% CI: 57-160%) for N retention (% of intake) and 98% (95% CI: 43-154%) for N retention (% of absorbed) on an equi-molar basis. In experiment 2, the overall average daily gain (ADG) and gain:feed ratio (G:F) increased linearly (P < 0.01) by supplementation with DL-Met or DL-Met-Met. The average daily feed intake increased by supplementation with DL-Met (P = 0.02) and DL-Met-Met (P = 0.09). For ADG, the RBV for DL-Met-Met was estimated 104% (95% CI: 66-141%) on an equi-molar basis by the slope-ratio. Based on G:F, the RBV for DL-Met-Met was estimated 117% (95% CI: 61-174%) on an equi-molar basis. The results of both experiments indicate that the bioavailability DL-Met-Met is not different and at least equally bioavailable as DL-Met as a Met source for pigs.
Feeding pigs with low protein diets is suggested to attenuate the negative effects of heat stress in pigs reared in hot climate areas, without changes on pigs performance. This study aimed to evaluate the nitrogen balance of pigs raised under tropical conditions and fed in conventional group-phase feeding systems (CON) or fed individually with daily tailored diets (IPF) receiving diets formulated with low (LCP) or high (HCP) crude protein. Sixty male castrated pigs (39kg±0.98) were assigned to 4 treatments in a 2×2 factorial arrangement. The experiment lasted 56 days (phase 1: d 0–28, and 2: d 29–56). CON fed pigs received within each phase a constant blend of diets A (high nutrient) and B (low nutrient density) supplying the estimated nutrient requirements of the group, whereas IPF pigs received daily a personalized blend providing the estimated amount of nutrients. Body lean was assessed by a dual-energy X-ray absorptiometry at the beginning and at the end of each phase and converted to body protein. Data were analyzed using the MIXED procedure of SAS including the fixed effects of feeding system, feed formulation, and their interactions. Pigs receiving LCP diets reduced the CP intake in 27% (P < 0.001). However, IPF pigs consumed on average 15% less CP than CON pigs (P < 0.001). Regardless of the reduced CP intake, LCP fed pigs showed a greater N retention than pigs receiving HCP diets during the first phase (P < 0.01). Moreover, pigs fed LCP diets excreted 30% less N to the environment than pigs fed HCP diets (P < 0.001). When LCP diets are complemented with the use of IPF technique, the N excreted can be reduced 18% more than in CON system (P < 0.001). Our results indicate that LCP diets and IPF are feasible to improve the nitrogen utilization of pigs raised under tropical conditions.
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