Photoperiodic time measurement is maintained in undernourished lambs with delayed puberty

Abstract

Beginning at 42 weeks of age undernourished females that had been maintained outdoors were exposed to long days (15L:9D) or short days (9L:15D). After 6 weeks, both groups were placed on short days, and ad-libitum feeding was begun. Rapid 'catch-up' growth occurred similarly in both groups. However, the response to oestradiol negative feedback regulation of LH secretion differed greatly. Short-day lambs remained hyperresponsive to oestradiol inhibition, and circulating LH remained low, a condition that typifies immaturity of the system governing LH secretion. In the females exposed to the long-day-short-day sequence, circulating LH began to increase 10 weeks after the end of long days; this change is characteristic of the neuroendocrine alteration that occurs during puberty. These findings indicte that the growth-retarded lamb can differentiate long days from short days, and can therefore continue to accumulate photoperiod information during prolonged periods of undernutrition.