RESUMEN
A competitive enzyme-linked immunosorbent assay [ELISA] kit was used for the evaluation of antibodies against Escherichia coliK99, rotavirus and coronavirus in colostrum samples of 240 non-immunized Holstein dairy cows in southern Tehran, Iran. Antibody levels against E. coli K99, coronavirus and rotavirus were higher than a 20% inhibition threshold in 76%, 99% and 100% of samples, respectively. From a total of 240 samples 14 cases [5.83%], 222 cases [92.5%] and 240 cases [100%] showed the strongest positive results [4[+]] for antibodies against E. coli, coronavirus and rotavirus, respectively. These colostrum samples were considered as high titre colostrum. The results showed that only a small number [5.83%] of colostrum samples had enough antibodies to protect the calves against diarrhea due to E. coli K99 after passive transfer. In the cases of rotavirus and coronavirus it was concluded that the colostrum samples obtained from non-immunized, naturally infected cows contained enough antibodies to develop passive immunity against rotavirus and coronavirus in suckling calves