RESUMEN
Off-sex, male Ross 308 chickens were offered maize-soy diets without and with 3.5 g/kg lysine monohydrochloride (HCl), which contained 10.0 or 12.8 g/kg digestible lysine, from 7 to 28 D post-hatch. Birds were permitted access to diets at intervals of 12, 16, and 20 h/day. Lysine HCl improved weight gain (1,465 vs. 1,417 g/bird; P < 0.025) and feed conversion ratios (1.351 vs. 1.382; P < 0.005). Extending feed access intervals increased weight gain (1,542 vs. 1,303 g/bird; P < 0.001) and feed intake (2,142 vs. 1,748 g/bird; P < 0.001) but compromised feed conversion ratios (1.390 vs. 1.342; P < 0.001). Extending feed access intervals increased (P < 0.001) both relative crop and gizzard weights and amounts of digesta retained in these organs. Effective lysine HCl utilization in poultry irrespective of feeding frequency, as opposed to pigs, may stem from anticipatory feeding behavior, crop and gizzard functionality, and increased episodes of reverse peristalsis. Collectively, these properties appear to modulate the relative intestinal uptakes of unbound lysine and protein-bound amino acids including lysine. Instructively, extending daily feed access intervals from 12 to 20 h increased average ileal digestibility coefficients of 16 amino acids by 12.8% (0.830 vs. 0.736; P < 0.001), which was linearly related (r = -0.834; P < 0.001) to hourly feed intake rates. Birds given 12 h feed access consumed relatively more feed on an hourly basis and this may have contributed to lesser amino acid digestibilities. As treatment interactions (P > 0.35) between lysine HCl and feed access intervals for parameters of growth performance were not observed, it was concluded that feed access intervals do not influence lysine utilization. The implications of these findings are discussed.