Influence of age and stage of gestation on serological response to subcutaneous or conjunctival Brucella melitensis strain Rev.1 vaccination in ewes

Abstract

Effects of age and stage of gestation on ovine serological response after administration of a low dose of vaccine were determined in sheep of the Churra breed. The animals were distributed into three groups by age: under 12 months, from 12 to 36 months, and over 36 months. Each of these groups was subdivided into three subgroups: the first group was vaccinated with 2.3 × 10 6 colony-forming units subcutaneously; the second group received the same dose by conjunctival route; the last group was kept as a control. The adult ewes (over 12 months) were separated into two groups by stage of gestation: pregnant and nonpregnant. These groups were subdivided as above. Blood samples were taken from every animal at the time of vaccination and at 4, 8,12, 24 and 36 weeks after vaccination. The serological tests used were Rose Bengal, complement fixation, and enzyme-linked immunosorbent assay. Serological response after vaccination was stronger and more persistent in animals vaccinated subcutaneously than in those receiving vaccine by a conjunctival route. This response was significantly different between the two groups. There were no significant differences in percentage of reactors between young and adult animals vaccinated subcutaneously. In the adult animals, a difference ( P < 0.05) in the level of antibodies of subcutaneously vaccinated sheep was noted between those aged over 36 months and those 12–36 months old only in Weeks 4 and 8 after vaccination. Animals under 12 months vaccinated conjunctivally had a weaker ( P < 0.05) serological response than those over that age. No differences were found between animals over 12 months vaccinated by the conjunctival route. There was no difference in serological response after vaccination between pregnant and non-pregnant ewes. Nevertheless, this response was always slightly greater in nonpregnant ewes. In conclusion, age is a factor which had an effect on the post-vaccinal response, but stage of gestation had no effect.