title: Positive effects of melatonin treatment on the reproductive performance of young border leicester rams mated to merino ewes in spring: preliminary observations.
abstract: Poor reproductive performance of Merino ewe flocks when mated to Border Leicester rams during spring may be due to seasonality of the Border Leicester breed. Two approaches were taken to test this assumption. Six young (12 months old) or six mixed-age (12, 24 and ≥36 months old) Border Leicester rams were either treated or not treated with melatonin implants (2 × 2 design) 6 weeks before the four groups of rams were each put with approximately 300 Merino ewes for an 8-week mating period. Implants were inserted in early September (experiment 1). The second approach was to yard or not yard ewes and mixed-age rams on several occasions during the first 3 weeks of the mating period (experiment 2). Pregnancy rate and twinning percentage were assessed by ultrasonography. In experiment 1, melatonin treatment in young rams increased (p < 0.001) pregnancy rate from 5.0% to 92.6%, but mixed-age rams did not respond (90.7% vs 89.5% for melatonin and non-melatonin treatments, respectively). Twinning rate was similar (p > 0.05) for ewes mated to either melatonin or non-melatonin-treated young rams (36.8% vs 40.0%, respectively), whereas melatonin significantly improved (p < 0.05) twinning rate in those ewes mated to mixed-age rams (49.1% vs 36.1%). After 6 weeks of melatonin treatment, scrotal circumference was greater (p < 0.05) in both young and mixed-aged rams than in untreated counterparts. In experiment 2, yarding of ewes and rams overnight on several occasions early in the mating period reduced (p < 0.001) pregnancy rate compared with non-yarded counterparts (89.5% vs 65.5%). Twinning rate was not affected (37.7% vs 36.1%, respectively). In summary, melatonin treatment of Border Leicester rams significantly improved flock reproductive performance in spring due to improved pregnancy rates with young rams and improved litter size with mixed-age rams.
authors.affiliation: Turretfield Research Centre, South Australian Research and Development Institute, Rosedale, SA, Australia.
authors.forename: D O
authors.initials: DO
authors.lastname: Kleemann
authors.forename: J M
authors.initials: JM
authors.lastname: Kelly
authors.forename: L J
authors.initials: LJ
authors.lastname: Arney
authors.forename: I L
authors.initials: IL
authors.lastname: Farley
authors.forename: A J
authors.initials: AJ
authors.lastname: Tilbrook
authors.forename: S K
authors.initials: SK
authors.lastname: Walker
mesh_terms: D000818:Animals; D004343:Drug Implants; D005260:Female; D005303:Fertility Agents, Male / Q000494:pharmacology*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple / Q000187:drug effects; D012621:Seasons; D012756:Sheep / Q000502:physiology*
chemical_list: D004343:Drug Implants; D005303:Fertility Agents, Male; D008550:Melatonin