Maturity of the Lamb Immune System

Abstract

Vaccines targeting specific threats to lamb health could be immensely instrumental in curbing high levels of lamb mortality in the U.S. lamb industry. However, the age at which vaccine administration would be most beneficial is currently unspecified due to limited knowledge of when lambs become immunocompetent. This study?s main objective was to determine the effect of age on the immunological competency of sheep in order to determine the optimal schedule for vaccinating lambs. An experiment was designed to examine the ability of lambs of varying ages to mount an antigen-specific immune response against Keyhole Limpet Hemocyanin (KLH) after vaccination with KLH in 10% aluminum hydroxide as the adjuvant. Groups of five lambs were vaccinated subcutaneously with one of three treatments (vaccine, control, adjuvant only) three times at two week intervals over a total of six weeks. The age at administration of the treatment was also variable (n=5); the lambs were either 0, 5, or 40 weeks of age at the start of their respective six week vaccine trial. Three blood samples were taken immediately prior to the second and third treatment and two weeks after the third. Lymphocyte proliferation, and production of total immunoglobulin (Ig), and KLH-specific Ig were measured. An increase in lymphocyte production in vaccinated animals in response to vaccines was seen as early as 4 weeks of age, after two vaccines. The production of anti-KLH Ab in vaccinated lambs began after the first vaccination and had a fold response four times as high as control and adjuvant-only animals when sampled two weeks after the first vaccination.