Duration of Melatonin Treatment Affects the Timing of Puberty in Young Red Deer Hinds

Abstract

The timing of puberty in farmed red deer (Cerus elaphus) hinds can be altered by the strategic administration of melatonin, and the present study was undertaken to investigate the importance of the duration of treatment. Six groups, each of five hinds aged about 12 months were used. The control group was untreated throughout while the remaining five groups received approximately 30, 60, or 90 days of melatonin from subcutaneous implants. Treatment began in three groups in spring (Non 30 November for 30, 60, ot 90 days), and in two groups in summer (on 30 December for 60 days and on 30 January for 30 days) so that each duration of treatment either started (30 November) or finished (approximately 1 March) at the same time. Treatment begun in spring lasting 60 or 90 days resulted in all hinds displaying ovarian activity about 20 March, representing about a 4-week advancement in the onset of puberty. Melatonin administered for 30 days in spring and 30 or 60 days in summer resulted in only a proportion (two or three of five) of hinds responding with early ovarian activity. In addition, melatonin treatment significantly advanced the seasonal patterns in live-weight gain and coat growth in some of the earlier treated groups, and reduced prolactin secretion in all treated groups. These results indicate that approximately 60 days of exogenous melatonin treatment is required to induce an alteration in the timing of puberty in red deer hinds, providing that it is given at an appropriate time of the year.