The effect of immaturity of the calf on immunological responses to strain 19 and killed 45/20 adjuvant vaccines.

Thirty brucellosis free calves with zero titres to the serum agglutination test (SAT), complement fixation test (CFT) and antiglobulin test (ABGT) were vaccinated with strain 19 at ages from seven hours to 198 days. Calves 75 days of age and older responded with normal serological patterns, developing high titres to all three tests. At 45 days and younger most calves responded with much reduced titres, some were negative to the SAT and CFT but all develped titres to the ABGT. Two of the younger group were subjected to an anamnestic test at about a year old and gave a positive response, indicating that the calf may be effectively primed with S19 as early as the first day of life. Three of the group were colostrumdeprived yet the patterns of their responses were similar to those of the colostrum-fed calves. Seventy-four zero titres calves were vaccinated with killed 45/20 adjuvant vaccine at ages from 60 to 320 days. Up to 200 days of age only seven of 33 calves gave positive response. From 200 to 280 days 18 of 29 responded and from 280 days of age all calves a positive response. The late development of competence to respond to this adjuvant vaccine is somewhat unusual and is discussed. It is suggested that the rough strain 45/20 may be a very weak antigen in cattle.