Field evaluation of melatonin implants to advance the breeding season in l-year-old farmed red deer hinds

Abstract

The efficacy of controlled-release melatonin implants to advance the onset of the breeding season was assessed in l-year-old red deer hinds on five commercial deer farms in various localities in the North Island of New Zealand. Between 44 and 60 hinds in each of six herds were equally divided among treatment and control groups at each site. Melatonin treatment commenced between 27 November and 16 December and was achieved by the subcutaneous administration of two 18 mg melatonin implants. Three doses were given at about 30 day intervals. Two adult stags for each hind group were treated with three 18 mg melatonin implants concurrently on either two or three occasions. On each property, treated and control hinds were joined as one herd to treated stags commencing 30 January–10 February and concluding 15 May–2 June. The hinds in the four experimental herds underwent rectal ultrasound examination May–June to estimate conception rate and foetal age. Calving dates, hind and calf mortalities, weaning weights, and the antler growth cycle and harvesting data were recorded.

Overall, treatment with melatonin resulted in an average advance of the median calving date of 22 days (range 12–36 days) when compared with untreated controls in the same herds. Pregnancy rates were 91.3–100% in treated hinds and 63.6–100% in untreated hinds. There were no differences in calf mortality or calf sex ratio between treated and untreated groups. No hind deaths could be attributed to melatonin treatment. The weaning weights of calves were 5.68 kg and 4.43 kg heavier for the male and female offspring of treated hinds respectively, compared with those of control hinds. Treated stags commenced rutting behaviour earlier than normal and the antler casting and growth cycle was advanced. Treatment resulted in advancement of the seasonal pattern of coat changes in hinds and stags, but no untoward side effects of the melatonin treatments were observed. (New Zealand Veterinary Journal 39, 23–8, 1991)