HERITABILITY ESTIMATIONS OF OSTEOCHONDROSIS IN THE TIBIOTARSAL JOINT AND OF BONY FRAGMENTS IN THE PALMAR PLANTAR PORTION OF THE METACARPOPHALANGEAL AND METATARSOPHALANGEAL JOINTS OF HORSES

Radiography of the tibiotarsal and meta- carpo- and metatarsophalangea l joints was performed on 753 Standardbred trotters (6 to 21 months ol d) born in 1988. The surveyed population was drawn at random from all parts of Norway and represented about 60% of Standardbred trotters bor n the same year. Osteochondrosis in the tibiotarsal joint was diagnose d in 108 (14.3%) horses, and the prevalence of disease in progeny grou ps > 10 ranged from 0 to 69%. Bony fragments in the palmar/plantar por tion of the metacarpo- and metatarsophalangeal joints were diagnosed i n 89 (11.8%) horses, and the prevalence of disease in progeny groups > 10 ranged from 0 to 41%. Heritability analysis was restricted to 644 horses, comprising groups of 5 or more progeny, from 39 stallions. The heritabilities of osteochondrosis in the tibiotarsal joint and of bon y fragments in the palmar/plantar portion of the metacarpo- and metata rsophalangeal joints were estimated to be 0.52 and 0.21, respectively, using a nonlinear model.