Ahemeral light cycles and protein levels for older laying hens.

Variations in light:dark ratios and timing schedules of 26- and 28-hr ahemeral cycles were examined for their effects on shell quality and egg weight. In two experiments utilizing 2578 White Leghorn Laying hens, 16-week long ahemeral treatments were instituted abruptly late in the pullet laying season and again following a forced-molt production cycle. Ahemeral light-dark cycles of 28-hr length resulted in significantly heavier shell and egg weights as compared to 26-hr ahemeral cycles or the control 24-hr cycle. Ahemeral 26-hr cycles did not significantly increase egg weight compared to the 24-hr controls but did increase shell weight. Varying total light in 28-hr cycles from 20 to 10 hr with the light given in either one continuous period or interrupted by two intermediate dark periods and as either 18 or 16 hr of continuous light in the 26-hr cycles did not result in significant differences in shell or egg weight compared to the other treatments of the same cycle length. Rate of lay was lower for the hens given only 10 hr of interrupted light in a 28-hr cycle but was not otherwise affected by light treatment. Dietary protein levels of 15% (as compared to 17%) and 14% (as compared to 16 and 18%) consistently reduced egg weights (P less than .10 or less than .05) and tended to improve shell quality. These experiments further demonstrated the effectiveness of 26- and 28-hr ahemeral light-dark cycles in increasing shell weight as a method of extending the economic laying period of either older pullets or force-molted hens without a sacrifice in the number of eggs produced.