WITHIN HERD ESTIMATES OF HERITABILITIES FOR 6 HOOF CHARACTERISTICS AND IMPACT OF DISPERSION OF DISCRETE SEVERITY SCORES ON ESTIMATES

Heritabilities and repeatabilities of six hoof traits were estimated f rom 10 years of routine hoof trimming data of a research dairy herd. H eritabilities were estimated by DFREML with an animal model on origina l scores and Snell transformed scores. A sire threshold model was also tested, but was numerically unstable due to the small number of obser vations per sire. Estimated heritabilities based on 3821 records of th e transformed scores were 0.05, 0.12, 0.06, 0.14, 0.02 and 0.08 for co rkscrew claw, heel erosion, interdigital dermatitis, laminitis, sole u lcers and white line separation, respectively; and repeatabilities wer e 0.17, 0.19, 0.15, 0.19, 0.14 and 0.14, respectively. Highly consiste nt results were estimated from original scores. Low heritabilities wit h a relatively large proportion of permanent environmental variance to additive genetic variance implied that response to selection for a si ngle score of corkscrew claw, interdigital dermatitis and sole ulcers would be small. Large proportions of environmental variances were cons istent with two hypotheses: (1) corkscrew claw may be influenced by ot her diseases or inappropriate hoof care and (2) interdigital dermatiti s or sole ulcers affect some cows repeatedly. Heritabilities of heel e rosion and laminitis were more than 10% and improvement by traditional quantitative methods should be possible.