EFFECT OF MELATONIN IMPLANTS, FLUSHING AND TEASING ON THE REPRODUCTIVE-PERFORMANCE OF SPRING-MATED DOHNE MERINO EWES

The effect of melatonin implants, flushing and teaser rams on the repr oductive performance of spring-mated Dohne Merino ewes was investigate d. The ewes (n = 534) were randomly allotted to four treatments, namel y (1) no treatment (control), (2) melatonim implants (melatonin), (3) flushing and teaser rams (flushing and teasers), and (4) melatonin imp lants, flushing and teaser rams (combined treatment). Ewes in groups 2 and 4 were implanted with melatonin 32 days before commencement of th e mating season (16 November 1990). In groups 3 and 4, ewes were suppl emented with 400 g of chocolate maize/head/day from three weeks before to the end of the mating period and vasectomized rams were introduced 10 days prior to mating. Conception rate, lambing percentage and fecu ndity were significantly higher (P < 0.05) in the melatonin treatment group (group 2) (93.5%, 105.4% and 1.13, respectively) than in control ewes (86.6%, 91.0% and 1.05, respectively). A higher (P < 0.05) lambi ng percentage was recorded in group 3 than in the control group (99.3% vs. 91.0%). When compared with the control treatment (5 December, SE +/- 4.5 days), the mean dates of the first recorded oestrus ('first oe strus') during mating were 21 November (SE +/- 1.6 days). 28 November, (SE +/- 3.98 days) and 30 November (SE +/- 5.14 days) for groups 2 (P < 0.01), 3 (P < 0.05) and 4 (P < 0.05), respectively. When compared w ith the control treatment (33 days), the spread of first oestrus was 1 8, 28 and 27 days for groups 2 (P < 0.01), 3 (P < 0.05), and 4 (P < 0. 05), respectively. However, no synergistic effect on reproduction and date of first oestrus above group 2 was found when melatonin-implanted ewes received the supplementation and stimulation with teasers (group 4). In animals treated with melatonin only (group 2) the onset of oes trus was earlier and the reproduction performance was higher than in o ther treatments (P < 0.05). At current prices melatonin treatment is m ore cost-effective than flushing and teasing.