We investigated the relationship between serological evidence of exposure to Campylobacter fetus (CF) and various indices of productivity in a cross-sectional study of 178 dairy cows from three California Dairy Herd Improvement Association (DHIA) herds. Blood samples were collected from the lactating cows during December, 1986. Enzyme-linked immunosorbent assay (ELISA) was used to determine antibody titers against CF, Haemophilus sommus (HS) and Leptospira hardjo (LH). The data on demographic and productivity parameters were obtained from DHIA individual-cow records of December, 1986. The data obtained pertained only to the current lactation of the cows. The variables CFETUS, HSOMNUS and LEPTO represent the serological status of a cow either as negative or positive against CF, HS and LH antigens, respectively. CFETUS represent the serological evidence of natural exposure to corresponding bacterial agents. However, LEPTO was assumed to be the level of vaccinal titer against LH since all the cows studied had been vaccinated routinely against this infectious agent during September, 1986. Five indices of productivity (recent calving interval, calving to conception interval, number of services per conception, test-day's milk production and percent mature equivalent milk production) were used. HSOMNUS, LEPTO and other covariates suggested by previous studies were included in modeling the relationships of interest. Stepwise multiple linear regression analyses were carried out to study the adjusted relationship of CFETUS with each measure of productivity. Multivariate analyses revealed that the adjusted relationships of CFETUS with recent calving interval, calving to conception interval, number of services per conception and test-day's milk production were non-significant. However, after adjusting for possible covariates, CFETUS-positive cows had an average of 7.43% less mature-equivalent milk production than CFETUS-negative cows. Among the covariates, LEPTO had a strong and independent relationship with recent calving interval and with percent mature-equivalent milk production (having unstandardized partial regression coefficients of -0.77 and 4.53, respectively). We conclude that the presence of antibodies against CF was not associated with reproductive efficiency of cows. The association of CF seropositivity with one index of milk production is the first indication that latent CF infection may be associated with subclinical mastitis (perhaps through a hypersensitivity reaction). However, this aspect needs further investigation.
ASJC Scopus subject areas
- Animal Science and Zoology