title: Melatonin rhythms in Pony mares and foals.
abstract: Melatonin concentrations in intact (N = 3) and sham-operated (N = 3) mares during March were greater (P less than 0 . 05) during the night than during the day, but this pattern was not seen in 3 mares from which the superior cervical ganglia had been removed bilaterally. When 4 Pony mares were exposed to a photoperiod of 10L:14D for 3 weeks and then to continuous darkness (0L:24D) for another 3 weeks, melatonin levels were greater (P less than 0 . 05) at the end of the 0L:24D period than during the earlier period and still displayed rhythmic fluctuations but were no longer co-ordinated with equivalent day/night rhythms or among mares. When melatonin rhythms were monitored in 3 mares and their foals housed in open pens exposed to natural lighting, significant time trends in melatonin concentrations were observed in mares when the foals were aged 1-3, 4-6 and 7-11 weeks, but foals did not display significant times trends in melatonin until they were 7-11 weeks old.
mesh_terms: D000375:Aging; D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D005260:Female; D005728:Ganglia, Sympathetic / Q000502:physiology; D006736:Horses / Q000502:physiology*; D008027:Light; D008550:Melatonin / Q000097:blood*; D010507:Periodicity; D012741:Sexual Maturation
chemical_list: D008550:Melatonin