PSXII-3 Amino acid profile of warm-season perennial grass-legume mixed pasture continuously stocked by horses

Abstract Providing an ideal amino acid profile to horses improves nitrogen (N) utilization and reduces N excretion. This 2-yr study investigated protein concentration and amino acid profile of forages during 84 d of continuous stocking of mixed pastures of rhizoma peanut (RP; Arachis glabrataBenth) and bahiagrass (BG; Paspalum notatumFlüggé) receiving 30 kg N/ha (RP-BG) compared with BG pastures fertilized with 120 kg N/ha (BG-N) or with no nitrogen fertilizer (BG-U). Forage samples were collected on d 0, 14, 28, 42, 56, 70, and 84. All data were reported as percent of crude protein on a dry matter basis. Histidine and phenylalanine were affected by an interaction between pasture and day (P = 0.023 and P = 0.044, respectively). Mixed pastures resulted in greater histidine than BG-N at d 56 (P = 0.016) and 70 (P = 0.002) and greater than BG-U at d 70 (P = 0.005). Phenylalanine did not present any clear pattern and was similar across pastures throughout most of the grazing season. RP-BG provided greater lysine (P < 0.01) than monoculture pastures (6.24 vs. 6.00), and arginine was greater (P = 0.007) in RP-BG than BG-U (5.24 vs. 5.12). RP-BG, however, resulted in lesser threonine (P = 0.017) than BG-U (4.76 vs. 4.86) and lesser methionine (P = 0.016) than BG-N (1.89 vs. 1.94). Regardless of the fertilization level, monoculture bahiagrass had greater (P = 0.015) leucine than RP-BG (9.48 vs. 9.29). There was a day effect on arginine (P < 0.001), isoleucine (P < 0.001), leucine (P < 0.001), lysine (P = 0.009), methionine (P = 0.005) and threonine (P < 0.001). Concentrations of all amino acids varied throughout the grazing season, with most peaking at d 14 and returning to initial values late in the grazing season. Threonine, however, increased (P = 0.001) by 5.4% from d 28 to d 84 (4.67 vs. 4.92). Results of this study indicate that intercropping rhizoma peanut into bahiagrass pastures may reduce environmental impacts by reducing nitrogen fertilization needs and improves lysine concentration. Greater lysine in forages is beneficial as lysine is the first limiting amino acid in horse diets.