TIMING OF MELATONIN TREATMENT - DIFFERENTIAL-EFFECTS ON ESTRUS AND COAT GROWTH IN GOATS

To avoid winter scarcity of fresh goat milk, simple methods of advanci ng the season of kidding would be commercially valuable. A combination of long-day light treatment followed by melatonin is successful but o ther aspects of seasonality including coat growth are also reset. To i nvestigate whether effects on breeding season and coat growth can be d issociated, British Saanen dairy goats (no. = 30) were randomly alloca ted to one of six groups. Control gents were untreated. Goats in the o ther five groups received 2 months of treatment with 20 h light : 4 h darkness (20L : 4D) and were then given 3 mg melatonin orally at 16.00 h for 2 months. The treatments started on 11 January (group 1), 29 Ma rch (group 2) 14 June (group 3), 30 August (group 4) and 8 November (g roup 5). Weekly blood samples were taken for the measurement of proges terone to monitor ovarian activity and prolactin. Side patches (10 cm x10 cm) were clipped monthly from alternate sides and weighed to measu re coat growth. The onset of ovarian activity was advanced from a medi an date of 15 November in controls to 24 May in group 1 (P < 0.01), 16 August in group 2 (P < 0.05) and 18 October in group 3 (P < 0.05). Gr oups 4 and 5 showed no significant change in the onset of oestrus (med ian onset dates 8 November and 1 November, respectively). Group 1 goat s came into season again with controls in November. In all except grou p 5, treatment interacted with time to affect significantly the growth of the coat. The pattern of coat growth was most altered IP < 0.001) in groups I and 2. This teas associated with effects on plasma prolact in concentrations of light stimulation and melatonin suppression. Grou p I gents resynchronized with control goats to show a coat of normal w eight in the winter following treatment. Division of milking goat herd s into spring and autumn kidding groups is, therefore, a practical pos sibility, but effects on overall milk yield require study.