CONGENITAL NEOSPORA-CANINUM INFECTION IN DAIRY-CATTLE AND ASSOCIATED CALFHOOD MORTALITY

A prospective cohort study was undertaken on two central California da iries, A and B, to estimate prevalence of congenital infection with Ne ospora caninum, to characterize temporal variation in prevalence, to d etermine if occurrence of congenital infection was associated with spe cific dam and calf attributes, and to estimate the effect of congenita l infection on calfhood mortality. Of the 405 calves enrolled over a p eriod of 2 1/2 y on dairy A and dairy B, 30.6% (85/278) and 53.5% (68/ 127), respectively, were seropositive precolostrally to N. caninum, as determined by an ELISA test. Adult cow seroprevalence at calving was 36.0% (82/228) for dairy A, and 57.9% (33/57) for dairy B. No evidence was found for a significant increasing or decreasing trend in adult a nd precolostral seroprevalence through the study period (P greater tha n or equal to 0.26). For both herds combined, 81% of seropositive cows (93/115) and 5% of seronegative cows (8/170) had congenitally infecte d calves. Seroprevalence did not increase with cow age on either dairy (P greater than or equal to 0.47). The probability of a calf being co ngenitally infected was not associated with dam age, dam lactation num ber, dam history of abortion, calf gender, or length of gestation (P g reater than or equal to 0.11). High dam ELISA values at calving were s ignificantly associated (P < 0.001) with an increased probability of c ongenital infection in her calf. Results of survival analyses of femal e calves available for follow-up indicated a consistently greater surv ivorship to 90 d in congenitally infected calves than in noninfected c alves on both dairies, which was significant for dairy A (P = 0.07, n = 186) but not for dairy B (P = 0.69, n = 72), thus indicating that co ngenital infection does not necessarily have a detrimental effect on c alf health. The findings of a similar magnitude in congenital infectio n rate and adult cow prevalence, the lack of increasing seroprevalence with cow age, the lack of an effect of dam age on precolostral seropo sitivity, and the constant seroprevalences during the study period, su ggest that, in the two dairies studied, congenital transmission consti tuted a substantial amount of infection and was likely the major mode of transmission of N. caninum.