title: Onset of puberty and duration of seasonal cyclicity in Lipizzan fillies.
abstract: BACKGROUND
  The onset of puberty and duration of seasonal cyclicity in Lipizzan fillies and young mares have been determined mostly by empirical data, but very little is known about the hormonal changes at puberty and during the seasonal cyclicity in this breed.
  
  
  OBJECTIVE
  To determine the onset of puberty and the course of the cyclicity in young Lipizzan mares from age 1-4 years.
  
  
  METHODS
  Blood samples were collected twice a month for 2 years from 46 Lipizzan fillies age 1-4 years. Progesterone concentrations, indicating ovarian activity, were measured using an EIA kit. Values above 6.4 nmol/l were taken to indicate luteal phase and those below 3.4 nmol/l, oestrus.
  
  
  RESULTS
  Fifty percent of Lipizzan fillies entered puberty during the first spring after their birth at mean +/- s.e. age 15.25 +/- 0.31 months and 50% during the second spring, at age 25.2 +/- 0.57 months. For several fillies of all ages, manifesting anoestrus during the winter months, the oestrus started in March and reached a peak in June to September. The duration of the oestrus activity was age-dependent, at 2.37 +/- 0.62 months in yearlings and 8.56 +/- 0.46 months in fillies age 4 years. In December, >50% of fillies age 2-4 years still exhibited oestrus activity and some entered anoestrus in January the following year. A small proportion of fillies age 3-4 years remained cyclic during the whole year, indicating that factors other than photoperiod can be involved in regulating seasonal cyclicity.
  
  
  CONCLUSIONS
  Our results demonstrate the influence of seasonal factors on the onset of puberty and on the course of oestrus activity in the majority of Lipizzan fillies. However, certain exceptions were also demonstrated but reasons for the prolonged periods of oestrus activity in some Lipizzan fillies were not identified, and the role of the hormone leptin should be studied in future investigations.
authors.affiliation: Institute of Physiology, Pharmacology and Toxicology, Veterinary Faculty, University of Ljubljana, Slovenia.
authors.forename: N
authors.initials: N
authors.lastname: Cebulj-Kadunc
authors.forename: V
authors.initials: V
authors.lastname: Cestnik
authors.forename: M
authors.initials: M
authors.lastname: Kosec
mesh_terms: D000367:Age Factors; D017668:Age of Onset; D000375:Aging / Q000097:blood / Q000502:physiology; D000818:Animals; D004971:Estrus / Q000097:blood / Q000502:physiology*; D005260:Female; D006736:Horses / Q000097:blood / Q000502:physiology*; D017440:Photoperiod; D011374:Progesterone / Q000097:blood; D012621:Seasons; D012741:Sexual Maturation / Q000502:physiology*
chemical_list: D011374:Progesterone