The aim of the study was to estimate breed and geneticeffects on the incidence of clinical mastitis (CM) in New Zealand dairy cattle. Records of CM collected during seasons 2005-06 to 2008-09 from 53,419 cows of different breeds including Holstein-Friesian (H-F), Jersey (J) and Crossbed (HF x J), were analysed. Clinical mastitis was coded “1” for cows that presented at least one event of CM at any day at risk during the season and “0” for cows without CM. Genetic parameters and breed effects for the incidence of CM were estimated with a repeatability animal model across breeds using restricted maximum likelihood methodology. The cumulative lactation incidence of CM was 11% in92,961 lactations. Heritability and repeatability for incidence of CM were 0.015 ± 0.003 and 0.070 ± 0.005, respectively. Jersey cowshad 2.9% less incidence of CM than H-F cows. Heterosis effect of H-F x J was minus 11.7% of the average of the parental breeds. Results from this study confirm previous estimates ofgenetic parameters for CM. Sire variation and breed and heterosis effects were significant and can be exploited in a breeding program to improve resistance to CM in New Zealand dairy cattle.

K, Jury, N Lopez-Villalobos, RJ Spelman, J Arias, and C Heuer

Proceedings of the New Zealand Society of Animal Production, Volume 70, Palmerston North, 246-249, 2010
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