Udder conformation and mastitis resistance in Danish first-lactation cows:Heritabilities, genetic and environmental correlations

Heritabilities, genetic and environmental correlations for nine conformatio n traits and six different measures of mastitis were estimated based on dat a from three populations: Danish Red (DR), Danish Holstein (DH) and Danish Jersey (DJ). The nine conformation traits were: fore udder attachment, rear udder width, udder cleft, udder depth, teat length, teat thickness, front teat distance, milking speed and dairy form. Conformation data were from th e official scoring of first-lactation cows for breeding value estimation of AI bulls in Denmark. Data from 11 306 DR cows, 60 438 DH cows and 10 639 D J cows were included. Mastitis treatments were measured in three periods: 6 0, 190 and 360 days of first lactation. In each period two measures were us ed: (1) no mastitis treatments or at least one mastitis treatment (binary); and (2) the number of treatments in the period (cumulative). Mastitis data were from the national Danish cattle database and included 84 593 first-la ctation DR cows, 374 191 first-lactation DH cows and 82 222 first-lactation DJ cows, parameter estimates were obtained using a sire model. Estimated h eritabilities for conformation and mastitis were in agreement with earlier Danish investigations. High genetic correlations between fore udder attachm ent, udder depth and dairy form and mastitis treatments were found for all three populations. For DR, DH and DJ correlations between fore udder and ma stitis in first lactation (360 days) were -0.42, -0.32 and -0.35, respectiv ely, The correlations between udder depth and mastitis in first lactation ( 360 days) were -0.53, -0.54 and -0.46, and between dairy form and mastitis in first lactation (360 days) were 0.35, 0.39 and 0.50. In a situation with mastitis registrations on 50 daughters and somatic cell count registration s on 100 daughters the accuracy (r(IA)(2)) of the mastitis resistance index is 46%. Including registrations of fore udder attachment, udder depth and dairy form from 40 daughters will increase the accuracy to 58%. In a situat ion with somatic cell count registrations on 100 daughters the accuracy (r( IA)(2)) of the mastitis resistance index is 27%. Including registrations of fore udder attachment, udder depth and dairy form from 40 daughters will i ncrease the accuracy to 48%.