Short communication: Genetic and nongenetic factors influencing Ostertagia ostertagi antibodies in UK Holstein-Friesian cattle

The purpose of this study was to estimate and discuss the genetic variation, heritability, and effects of nongenetic factors on the ability of Holstein-Friesian cows to produce an immune response by producing IgG antibodies to Ostertagia ostertagi. Total IgG (IgG1 and IgG2) antibody levels were determined using an ELISA and measured using optical density ratio (ODR = ODsample - ODnegative control/ODpositive control - ODnegative control) from milk samples collected from 1,276 Holstein-Friesian cattle in 229 commercial dairy farms from 2002 to 2004 during their first (82%) and other (2 to 12) lactations. A sire (n = 461) model was fitted to the ODR data using ASREML software, and variance components were estimated. The ability to produce O. ostertagi antibodies as measured by ODR had a heritability of 0.13 ± 0.12, and both season of sample and herd had a significant effect on total IgG levels. To conclude, this study has ascertained that genetic variation is present in the ability of dairy cows to mount an immune response to the parasite O. ostertagi. Inasmuch as evidence exists that IgG is linked to protective immunity against the parasite via a reduction in its reproductive ability, this trait may be of potential interest to genetic selection programs as an aid to reduce the effect of O. ostertagi in dairy herds.