title: Comparison of the blood supply to the articular-epiphyseal growth complex in horse vs. pony foals.
abstract: BACKGROUND
  To increase understanding of why the prevalence of clinical/radiographic osteochondrosis (OC) dissecans is high in horses and low in ponies.
  
  
  OBJECTIVE
  To investigate whether the clinical difference in OC occurrence between horses and ponies could partly be explained by a difference in: 1) number of patent vessels in the epiphyseal growth cartilage; 2) duration of the presence of patent cartilage canals; or 3) growth cartilage thickness at predilection sites for OC. The hypothesis was that pony foals would have fewer cartilage canals, shorter duration of blood supply and thinner growth cartilage than horse foals.
  
  
  METHODS
  Observational, cross-sectional study.
  
  
  METHODS
  Nine Standardbred foals (horse group) 1-49 days old and 11 Norwegian Fjord foals (pony group) 1-62 days old were included. A total of 15 anatomical locations in the tarsocrural and metatarsophalangeal joints were examined by one or more of the following techniques: arterial perfusion; photography of cleared specimens; microcomputed tomography; radiography; and histology. The number of cartilage canals was counted. Cartilage thickness was measured. Duration of blood supply was assessed in histological sections.
  
  
  RESULTS
  Of the 3 common predilection sites for OC investigated, there were significantly fewer vessels (P = 0.003) and thinner cartilage (P = 0.002) at the distal lateral trochlear ridge of the talus in the pony group. There was no difference in the duration of presence of cartilage canals between the groups.
  
  
  CONCLUSIONS
  The hypothesis that pony foals would have fewer cartilage canals and thinner growth cartilage than horse foals was confirmed for the lateral trochlear ridge of the talus. The current results may contribute towards an explanation for the low prevalence of OC at the distal lateral trochlear ridge of the talus in pony foals.
authors.affiliation: Department of Companion Animal Clinical Sciences, Norwegian School of Veterinary Science, Oslo, Norway.
authors.forename: E H S
authors.initials: EH
authors.lastname: Hendrickson
authors.forename: K
authors.initials: K
authors.lastname: Olstad
authors.forename: A
authors.initials: A
authors.lastname: Nødtvedt
authors.forename: E
authors.initials: E
authors.lastname: Pauwels
authors.forename: L
authors.initials: L
authors.lastname: van Hoorebeke
authors.forename: N I
authors.initials: NI
authors.lastname: Dolvik
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D049628:Body Size / Q000502:physiology*; D003430:Cross-Sectional Studies; D006132:Growth Plate / Q000098:blood supply*; D006736:Horses / Q000254:growth & development* / Q000502:physiology*; D013643:Tarsus, Animal / Q000098:blood supply*
keywords: cartilage canals; foal; horse; metatarsophalangeal joint; osteochondrosis; tarsocrural joint