Effect of melatonin implants, flushing and teasing on the reproductive performance of spring-mated Dohne Merino ewes

摘要

The effect of melatonin implants, flushing and teaser rams on the reproductive performance of spring-mated Dohne Merino ewes was investigated. The ewes (n = 534) were randomly allotted to four treatments, namely (1) no treatment (control), (2) melatonin implants (melatonin), (3) flushing and teaser rams (flushing and teasers), and (4) melatonin implants, flushing and teaser rams (combined treatment). Ewes in groups 2 and 4 were implanted with melatonin 32 days before commencement of the mating season (16 November 1990). In groups 3 and 4, ewes were supplemented 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 fecundity 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) lambing 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 oestrus`) 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 with the control treatment (33 days), the spread of first oestrus was 18, 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 oestrus was earlier and the reproduction performance was higher than in other treatments (P < 0.05). At current prices melatonin treatment is more cost-effective than flushing and teasing.