The time factor in egg formation for hens exposed to ahemeral light-dark cycles

Three hundred and two White Leghorn pullets were killed at intervals 5 min to 7 h following oviposition. The reproductive tract was then examined and, from the position of the yolk, estimates were made of the mean time spent by the ovum in different parts of the oviduct. Half the birds examined had been kept under 24‐h cycles (14 h light : 10 h dark) and half under 27‐h cycles (14 h light : 13 h dark). Mean intervals from oviposition to ovulation were 24 min and 36 min for birds under 24‐h and 27‐h cycles respectively. The difference between these values can be associated with the different rates of lay of birds under the two treatments. Mean times spent in the upper oviduct and the shell gland were estimated as 5·15 h and 19·76 h for the 24‐h cycles and 5·41 h and 20–70 h for the 27‐h cycles. The increase in albumen weight which has been reported to follow from the use of 27‐h cycles can thus be associated with extra time spent in the magnum. The reported increase in shell weight of 10% is more than would be expected from a 5% increase in time spent in the shell gland.