Serological profile of colostral antibodies to Neospora caninum in infection free calves

Abstract

Neospora caninum is considered the main cause of bovine abortion worldwide. The correct laboratorial diagnose is very important to identify the infected animals and to apply control measure. The objetive of this study was to show the persistence period of colostral antibodies in calves. Eight newborn Holstein Friesan calves, males, were selected from N. caninum soronegative dams. Pre-colostral blood samples were collected of these calves and all of them were seronegative to N. caninum. They were fed with two liters of pooled colostrum from seropositive cows within two hours after birth. Blood samples were collected and tested weekly until the animals turned negative. Serum samples were tested for antibodies to N. caninum using indirect fluorescence antibody test at 1:50; 1: 100 and 1:200 dilutions. Antibodies were not detected from three out of eight calves and they were excluded from the study. The remaining 5 calves seroconverted in all dilutions at the fifth day after colostrums ingestion. At 1:50 dilution, one calf remained positive for 21 weeks, two for 20 weeks and one for 13 weeks. At 1:100, one calf was positive for 15 weeks and the remaining 4 calves for 13 weeks. At 1:200, each calf was positive for 1, 7, 12, 12 and 13 weeks, respectively. These results demonstrate that the colostral antibody to N. caninum may persist until 21 weeks after birth in calves and it's very important to exclud the calves at the first month of age in the seroprevalence studies to avoid the false-positive results.