Effects of a shortened daily photoperiod or melatonin treatment on pubertal red deer hinds (Cervus elaphus)

Abstract

The effects of a shortened daily photoperiod or daily, afternoon injection of melatonin on the the onset of the breeding season and other seasonal changes associated with the transition from summer to winter were examined in pubertal red deer hinds. Eleven pubertal hinds and four non lactating adult hinds were randomly allocated to three treatment groups. Control hinds (Group 1) were maintained under natural photoperiodic conditions. From 8 January until 31 March one group of hinds (Group 2) was subjected to a daily photoperiodic regime of eight hours light to sixteen hours dark (8L:16D) by keeping them in a darkened room from 1600h until 0800h the following day and another group of hinds (Group 3) was given an intramuscular injection of 3 mg melatonin in safflower oil daily at 1600h. Silent ovulations seemed to occur in many of the hinds, but this study did not establish whether the treatments utilised here had any effects on these silent ovulations. Earlier calving may give rise to calves with a body weight advantage over those born later, at least until their first winter. Mating and calving data from the adult hinds was too limited to indicate whether the advancement of these events achieved in the yearlings could readily translated to older animals.