title: Relationship between stages of the estrous cycle and bone cell activity in Thoroughbreds.
abstract: OBJECTIVE
  To investigate the relationship between stage of estrous cycle and bone cell activity in Thoroughbreds.
  
  
  METHODS
  Blood samples collected from forty-seven 2-year-old Thoroughbred mares in training for racing.
  
  
  METHODS
  Blood samples were collected monthly (in April through September) from the mares. Stage of estrus was determined by assessing serum progesterone concentration. Bone cell activity was determined by measuring concentrations of 2 markers of bone formation (osteocalcin and the carboxy-terminal propeptide of type I collagen [PICP]) and a marker of bone resorption (the cross-linked carboxy-terminal telopeptide of type I collagen [ICTP]) in sera.
  
  
  RESULTS
  When the relationship between stage of the estrous cycle and markers of bone cell activity was examined, serum concentrations of both osteocalcin and ICTP were significantly higher in mares that were in the luteal phase, compared with mares that were at other stages of the estrous cycle. Stage of estrus did not affect serum PICP concentration.
  
  
  CONCLUSIONS
  Results indicate that bone cell activity in Thoroughbred mares fluctuates during the estrous cycle; serum concentrations of markers of bone formation and bone resorption are increased during the luteal phase. Further studies are required to determine whether these changes are of clinical importance and increase the risk of injury for mares in training during the breeding season. As in humans, stage of estrus must be considered as a source of uncontrollable variability in serum bone marker concentrations in horses.
authors.affiliation: Department of Veterinary Clinical Sciences, The Royal Veterinary College, London, NW1 OTU, England.
authors.forename: Brendan F
authors.initials: BF
authors.lastname: Jackson
authors.forename: Philip K
authors.initials: PK
authors.lastname: Dyson
authors.forename: Rachael D
authors.initials: RD
authors.lastname: Hattersley
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Kelly
authors.forename: Dirk U
authors.initials: DU
authors.lastname: Pfeiffer
authors.forename: Joanna S
authors.initials: JS
authors.lastname: Price
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology*; D024042:Collagen Type I; D030762:Estrous Cycle / Q000502:physiology*; D005260:Female; D006736:Horses / Q000097:blood / Q000502:physiology*; D015675:Osteocalcin / Q000097:blood; D010446:Peptide Fragments / Q000097:blood; D010455:Peptides; D010805:Physical Conditioning, Animal / Q000502:physiology; D011347:Procollagen / Q000097:blood; D011374:Progesterone / Q000097:blood; D012621:Seasons
chemical_list: D024042:Collagen Type I; D010446:Peptide Fragments; D010455:Peptides; D011347:Procollagen; C052929:collagen type I trimeric cross-linked peptide; C042813:procollagen type I carboxy terminal peptide; D015675:Osteocalcin; D011374:Progesterone