Techniques for monitoring dairy calves against the tick fever agents: a comparative analysis.

Data regarding parasitemia (blood smears), rectal temperature (RT), packed cell volume (PCV) and vaginal mucosa coloration (VMC) of Gyr x Holstein female calves between 3-7mo were accessed to evaluate different techniques for monitoring the bovine tick fever agents (TFA). The 1st experiment determined the correlation between the TFA parasitemia with RT and PCV. The 2nd, evaluated the associated risk of A. marginale parasitemia with RT and PCV in relation to the Gyr/Holstein genetic proportion (5/8,3/4,7/8 and 15/16) using Receiver Operating Characteristic Curve (ROC). The 3rd, two groups were performed: cattle monitored by RT (T01) and by PCV (T02), during their 80-210 days of age, data regarding TFA parasitemia, RT, PCV, VMC and weight were registered. In 1st experiment, RT showed weak correlation with TFA parasitemia, while PCV showed a strong correlation with A. marginale and B. bigemina, but not with B. bovis parasitemia. In experiment 2, the ROC curve analysis showed that when the genetic proportion of B. t. taurus increased, least reliable RT was to monitor calves infected with A. marginale. The PCV for monitoring A. marginale was the best technique, showing sensitivity of 74.2% and specificity of 97.0% than other techniques that used RT and VCM as a monitoring tool. In general, calves monitored by PCV (T02) showed higher PCV values, lower A. marginale parasitemia, less pneumonia as co-infection and less salvation treatment were performed than in animals monitored by RT (T01). Furthermore, animals from T02 gained 23.5 kg more than those from T01. The low frequency of B. bovis and B. bigemina found in this study made impossible to compare the monitoring techniques for these pathogenic agents.