Abstract
Effect of photoperiod and food duration on body weight gain, energy intake, energy expenditure, and sexual development were investigated in two strains of Japanese quail ( Coturnix c. japonica), bred for meat (broilers) or egg production (layers), from 7 to 71 days of age. In a first experiment chicks were subjected to 18L:6D, 15L:9D, 12L:12D, 9L:15D, or 6L:18D, with ad lib food during the light period. In a second experiment birds were exposed to a long photoperiod (18L:6D or 15L:9D) with ad lib food during part of the light period (first 6 or 9 h, respectively). Longer photoperiods were associated with larger weight gains. In 18L:6D broilers total body weight gain was 262 g compared to 213 g in 6L:18D broilers. In layers, corresponding values were 182 and 131 g. This effect of photoperiod on weight gain was primarily due to the effect of photoperiod on food availability. The photoperiod below which detrimental effects on weight gain occurred was 9L:15D for both strains. Chicks subjected to 9L:15D or 6L:18D exploited crop filling to enhance energy intake. They also decreased nocturnal metabolic rates to a greater extent compared to levels during the light phase than chicks subjected to light periods of 12 h or more. Sexual maturation was stimulated by photoperiod. At the age of 71 days, eight out of nine females subjected to 18L:6D were producing eggs, but none of the 6L:18D females. It is concluded that changes in feeding behavior and energy expenditure shown under short photoperiods are part of a strategy that allow chicks to gain weight continuously.
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