Effects of DL-Methionine or Methionine Hydroxy Analogue-Free Acid Supplementation on Growth Performance and Carcass Yield of Broilers Fed Reduced Energy Diets with Guanidinoacetic Acid Supplementation

Guanidinoacetic acid (GAA) and methionine are two biologically active compounds related to cell energy metabolism. Both are metabolically linked, as the methyl group needed to transform GAA into creatine derives from S-adenonsylmethionine out of the homocysteine cycle. A broiler feeding study was conducted to evaluate potential interactions between 600 g/t supplemental GAA and feed additives with methionine activity. The experimental design comprised two parts. Part one consisted of three dietary treatments in which DL-methionine (DL-Met) was added to meet sulfur amino acid recommendations (1), DL-Met was replaced with liquid methionine hydroxy analogue-free acid (MHA-FA) assuming an 80% methionine activity in the product (2), and DL-Met was added at 65% of the MHA-FA dose used in Treatment 2 (on a product weight basis). Treatments 1, 2, and 3 reflect the range of commercial practice with assuming bioefficacies of either 80% (Trt 2 vs. 1) or 65% (Trt 3 vs. 2) for MHA-FA relative to DL-Met. Part two followed a 2 × 4 factorial design. Either DL-Met or MHA-FA (assuming 80% methionine activity) was added to diets with gradually reduced apparent metabolizable energy (AME; standard, −25, −50, −75 kcal/kg AME). For MHA-FA, a bioefficacy of 80% relative to DL-Met was applied in order to evaluate interactions with GAA efficiency assuming inadequate dietary Met+Cys supply with MHA-FA. AME-reduced diets were supplemented with 600 g/t GAA to evaluate its energy-sparing potential. A total of 2784 male Cobb 500 broilers were equally assigned to 116 floor pens, resulting in 13 replicates (one treatment with 12) per treatment. A five-phase feeding program was introduced from 1 to 40 days of age. Body weights (BW) and feed intake (FI) were recorded in weekly intervals allowing for calculating weight gain (BWG) and feed conversion ratio (FCR). At termination of the experiment, three birds per pen were obtained for carcass analysis. The results revealed that an overestimation of the bioefficacy of MHA-FA relative to DL-Met significantly compromised broiler growth (p < 0.05), while applying a bioefficacy of 65% for MHA-FA relative to DL-Met65 resulted in similar performance. However, on day 40, BW of broilers fed DL-Met65 were higher than with MHA-FA (p < 0.05). It is concluded that an overestimation of the bioefficacy of MHA-FA relative to DL-Met bears the risk of compromised broiler performance while a bioefficacy of 65% allows at least similar, potentially even better, performance and economic advantages. There were basically no interactions between MHA-FA or DL-Met and graded ME levels with concomitant GAA supplementation regarding overall performance of broilers. This means that final BW of DL-Met-fed broilers were higher than those of MHA-FA broilers independent of dietary ME (p < 0.05). In early feeding phases, interactions indicated that broiler performance (BW day 7, 21, p < 0.05) diminished with dietary energy reduction with DL-Met supplementation while this was not the case with MHA-FA-fed broilers. However, with standard AME, DL-Met outperformed MHA-FA (p < 0.05). Basically, GAA supplementation compensated AME reduction up to 50 kcal/kg as there were no differences in BW, BWG, FCR, FI, or breast meat yield. Additionally, −75 kcal/kg AME was compensated by GAA only up to a broiler age of 21 days.