Transmission of bovine herpesvirus 1 (BHV1) within and between herds was studied on the island of Ameland, The Netherlands. There were 50 herds with 3300 head of cattle on the island. Herds were divided into three groups : (1) only containing seronegative cattle, (2) containing seronegative cattle and vaccinated seropositive cattle, and (3) containing only vaccinated cattle. All 23 herds in groups 1 and 2 were monitored. Three major outbreaks of BHV1 infections were observed due to the introduction of infectious cattle. Another major outbreak was most likely induced by reactivation of latent BHV1 in seropositive cattle. The basic reproduction ratio within these herds was estimated at least 4. Only one of these outbreaks led to three secondary outbreaks in susceptible herds in which all cattle were seronegative. These outbreaks were most likely due to respectively, direct animal contact, human transmission, and aerogenic transmission. The basic reproduction ratio between herds in this study was estimated to be 0 . 6.

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A vaccine containing inactivated cultures of Bordetella bronchiseptica, toxigenic Pasteurella multocida type D and dermonecrotic P multocida type D toxoid in an oil-in-water adjuvant was given to seven sows, with seven others acting as controls. Half the piglets in each litter were exposed intranasally when four days old to B bronchiseptica and when eight days old to toxigenic P multocida type D. There was considerably less sneezing in the litters of the vaccinated sows and when the piglets were 10 weeks old, only 18 per cent had deformed snouts compared with 74 per cent in the litters of the control sows. The average liveweight gain of the piglets born to vaccinated sows was significantly better (P less than 0.05) between two and 10 weeks of age than that of the piglets born to unvaccinated sows, although there were no significant lower respiratory tract lesions in either group. The conchal atrophy scores were significantly lower (P less than 0.001) in the piglets from the vaccinated sows and were negatively correlated (r = -0.37) with increasing liveweight gain. In the liters of the vaccinated sows, P multocida was not isolated from the nasal passages of the in-contact piglets and from only 7 per cent of those deliberately exposed compared with 65 per cent and 79 per cent, respectively, in the litters of the control sows. P multocida was isolated post mortem from the tonsils of 23 per cent of the piglets of vaccinated sows and from 87 per cent of those from unvaccinated sows.

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Summary A sero‐epidemiological survey of Bovine Respiratory Syncytial Virus infections in calves was carried out on 123 dairy farms in the Netherlands. During the last weeks of November 1983 5 first season grazing calves per farm were blood sampled. The presence of antibodies against the Bovine Respiratory Syncytial Virus (BRSV) was determined by the Enzyme Linked Immuno Sorbent Assay. The mean extinction values per farm were related to farm‐herd‐ and management characteristics. It was found that 1) On 95% of the farms the calves were infected with BRSV before mid‐November. 2) On 20% of the farms calves showed serious clinical signs of BRSV. 3) On farms with clinical BRSV disease history calves have more risk of acquiring a clinical BRSV infection. 4) Vaccination against BRSV disease did not influence the occurrence of BRSV infections. 5) There was a negative relation between contact of calves with older cattle and the onset of a clinical BRSV infection. Zusammenfassung Sero‐epidemiologische Untersuchungen mit dem bovinen Respiratory Syncytial‐Virus bei Rindern nach dem ersten Weidegang Eine epidemiologische Untersuchung mit Seren auf Infektionen mit dem bovinen Respiratory Syncytial‐Virus wurde in 123 Milchbetrieben in den Niederlanden durchgeführt. Während der letzten zwei Novemberwochen 1985 wurden Blutproben von 5 Kälbern pro Farm nach dem ersten Weidegang entnommen. Das Vorhandensein von Antikörpern gegen bovines Respiratory Syncytial‐Virus (BRSV) wurde mit dem Enzym‐Immunosorbent‐Test (ELISA) überprüft. Die ermittelten mittleren Extinktionswerte in einzelnen Betrieben wurden in Relation gesetzt zu den Betriebs‐, Herden‐ und Management‐Charakteristika. Es wurde festgestellt, daß: 1. In 95% der Betriebe die Kälber vor Mitte November mit BRSV infiziert wurden. 2. In 20% der Betriebe die Kälber deutliche klinische Erscheinungen einer BRSV‐Infektion zeigten. 3. In Betrieben mit früheren BRSV‐Krankheitsfällen die Kälber einem höheren Risiko einer klinisch manifesten BRSV‐Infektion ausgesetzt sind. 4. Die Impfung gegen die BRSV‐Erkrankung keinen Einfluß auf das Auftreten von BRSV‐Infektionen hatte. 5. Eine negative Beziehung zwischen dem Kontakt von Kälbern mit älteren Rindern und dem Auftreten einer klinisch manifesten BRSV‐Infektion besteht.