Transmission of Brucella ovis from rams to red deer stags

To determine whether B. ovis will transmit from infected rams to non-infected red deer stags (Cervus elaphus) grazing together in the same paddock.

Six rams artificially infected with B. ovis were grazed with six non-infected 14-month-old red deer stags for a four and a half month period from March 4 to July 20, 1999. Stags were blood sampled at one- to six-weekly intervals to test for B. ovis antibodies using a complement fixation test. Stags that seroconverted were semen sampled to test for B. ovis infection by bacteriological culture.

Between day 92 and day 124 of grazing together (June 4 and July 6), sera from five of the six stags became positive in the B. ovis complement fixation test. B. ovis was cultured from semen samples from four of the seropositive stags.

Brucella ovis can be transmitted from infected rams to non-infected stags grazing in the same paddock, suggesting that B. ovis infection in farmed deer in New Zealand initially came from infected rams. Whether transmission occurs from direct contact between rams or stags, or indirectly by environmental contamination needs to be established.