Summary
In response to complaints of the potential side-effects of the bivalent live-modified vaccine used to control the spread of bluetongue (BT) virus (BTV) serotypes 2 and 9 in Italy, a study was conducted to determine the effects of immunisation on milk production. Thirty-four Comisana cross-bred sheep were vaccinated with the bivalent BTV-2/BTV-9 modified-live vaccine produced by Onderstepoort Biological Products in South Africa; six animals served as unvaccinated controls. All animals were bled twice a week for two months and the presence and titres of BTV in the blood determined. The somatic cell count, pH, fat, protein and lactose content of the milk, as well as the quantity of the milk produced, were also measured. Vaccine virus was isolated from vaccinated animals between day 3 and day 20 post vaccination (pv) with peak titres observed on days 3 and 6 pv for BTV-2 and BTV-9, respectively. Milk production declined in the vaccinated group between days 8 and 14 pv, with the greatest decrease on day 9 pv. No differences were observed in the somatic cell count and pH, or in the milk fat, protein and lactose content.

Keywords
Bluetongue, Italy, Lactose, Milk fat, Milk pH, Milk production, Milk protein, Sheep, Somatic cell count, Vaccine, Virus, Viraemiae.