The clinical and pathological findings after a natural intra-uterine infection with BVD-virus in a Friesian dairy herd are described. The virological and serological aspects will be discussed in a separate paper (30). In a period of 4 years, 11 calves were born with the following nervous symptoms: more or less serious incoordination, tremor, oscillating nystagmus, and a negative blinking reflex. The pupillary and sucking reflexes were normal. No ocular defects, such as lenticular opacity or retinal atrophy were observed. The first calf was born in 1979. Within 6 months the symptoms disappeared. After a normal conception and pregnancy this animal gave birth to 2 clinically normal calves in 1981 and 1982. The second calf died at the age of 2 months, due to an ulcerating enteritis. In 1980, again 8 calves with the same nervous symptoms were born within a period of 3 months. Two calves died at the age of 3 days and 5 weeks respectively; 2 calves were sold when 10 days and 3 weeks old; one calf did not improve and was necropsied at the age of 17 days. The remaining 3 calves showed only a slight hypermetria when examined after 6 months. At that time nystagmus was only visible with ophthalmoscopy. Two calves were slaughtered when 10 months old. The last one, a bull, proved to be sterile and was necropsied at the age of 1 1/2 year. A calf, born in 1981, recovered within a week and was necropsied at the age of 15 days. The last calf, born in 1982, did not improve at all and was necropsied at the age of 14 days. During these 4 years none of the other animals in the herd showed any symptoms due to an acute or chronic BVD-virus infection. At post mortem examination of 6 animals no macroscopically visible malformations were found. Hypomyelination and abnormal glial cells were evident in 5 cases, especially in the two youngest calves which did not show any improvement. One of them had had an obvious thymic hypoplasia. The calf which recovered within a week showed only very slight changes. In one of the calves slaughtered at 10 months, inflammatory lesions were found in the brain. The diagnosis was confirmed by virological investigations. Clinically as well as pathologically there was a close resemblance to Border disease in lambs and congenital tremor in piglets after prenatal exposure to Hog cholera virus.

SUMMARY The results are described of virological and serological research carried out in a Dutch dairy herd during a number of years. The motive was the birth of a number of calves with neurological disorders pointing at an intra-uterine infection with BVD-virus in 1980. Also in the previous and in both the following years a calf was born with similar symptoms. The clinical signs and the course of the affection in these eight calves were described in a previous paper (2). The diagnosis was confirmed through virus isolation from pre-colostral blood of one calf and from autopsy material from four aberrant calves. During the investigation three clinically normal animals with a persistent virus infection were found. The clinically recovered animal of 1979 also proved to be a virus carrier. In addition, in two animals a transient viremia in the presence of specific antibodies was found. The four virus carriers conceived normally. The second pregnancy of the oldest animal also passed normally. Their five calves proved to be BVD-virus carriers as well. One calf, born in 1982, showed nervous disturbances to a serious extent. Of the four other clinically normal animals, one calf was euthanasized because of a serious necrotizing enteritis. The remaining calves stayed healthy and grew up normally. One of the two animals with a transient viremia wasfive months pregnant at that moment. At birth in 1981 her calf showed nervous disorders, but both the virological and the serological examinations of the pre-colostral blood were negative.