Unusual observations on a serologically negative bluetongue virus infected bull

A Holstein bull named "Regency" born in New York in July 1968, maintained in an artificial insemination (AI) stud for 9 years, unremarkable from the point of view of health history or semen production, was discovered "by accident" to have bluetongue (BT) virus (BTV) in his semen. A microscopic study in 1975 and 1977 revealed unusual cytoplasmic vacuoles in the sperm of "Regency" prompting us to send semen to A. J. Luedke, USDA-ARS, Denver, Colorado, USA, to attempt virus isolation. Serotype 13 BTV was isolated from the semen. Serum sent with the semen was negative for antibody by the agar gel immunodiffusion (AGID) and complement fixation (CF) tests. Annual AGID serologic tests begun in 1975 and continuing to the present have been negative for antibody to BTV for all bulls in this AI stud. "Regency" was moved to Auburn, Alabama, USA in 1978 and further studies were performed. The bull was maintained with the Veterinary School herd. The BT serologic status of the cattle did not change during the year the bull was in the herd nor were the cows he bred or their calves serologically positive for BT. Studies on insemination of cattle with experimentally contaminated semen indicated that 5X10(4) infectious doses of BTV were required for infection. These results suggest that since "Regency's" semen did not infect cows, the semen probably contained less than this amount of virus. The rete testis was cannulated, rete fluid collected, a testis removed and virus isolation attempted.(ABSTRACT TRUNCATED AT 250 WORDS)