Abstract
In oder to elucidate age-related changes in the humoral immunity of beef cattle, IgG1, IgG2, IgA, and IgM levels in the serum and colostrum, and the yield of colostrum were determined in heifers and cows of Japanese Black and Japanese Shorthorn at various ages from 6 months to 14 years of age. Serum Ig levels increased remarkably up to 28±5mg/ml for Japanese Black and 33±6mg/ml for Japanese Shorthorn over 12 years of age, and those increases were markdly high during the first 4 years of age. The shapes of the changes in serum Igs with age were different for each Ig classes and breeds. There was a marked increase in IgG2 concentration in serum compared with small increase in IgG1 and IgA during the normal life span, but there was no apprent effect of age on IgM concentration. Three Ig classes in colostrum except for IgG2 were higher than those in serum, but those levels decreased rapidly to the levels in normal milk within 3 days after parturition. Significant differences between breeds and age were found in Igs concentration and in yield of colostrum. Japanese Shorthorn had higher colostrum yield but had lower Igs level in colostrum. On the other hand, Igs level in colostrum and yield of colostrum were significantly higher in older cows than that in younger cows. These results indicate that the humoral immunity in beef heifer developes with age and come to immunological maturity until about 4 years of age. The data also suggest that the neonatal calves from older cows may acquire more passive immunity than those from younger cows as a result of age-related development of the dam's humoral immunity.
