Sensitivity and specificity of the FAMACHA system in tropical hair sheep.

The aim of this research was to evaluate the sensitivity and specificity of the FAMACHA (F) system in Morada Nova ewes. The conjunctivae of 562 ewes were evaluated using the F system. Packed cell volume (PCV) served as the gold standard for clinical F evaluation. To calculate the sensitivity and specificity of the F system, different criteria were adopted: animals classified as (I) F 4 and 5 or (II) 3, 4, and 5 were considered to be anemic and animals classified as (I) F 1, 2, and 3, or (II) 1 and 2 were considered to be non-anemic. Three standard values of PCV, namely, ≤ 19%, ≤ 18%, or ≤ 15%, were used to confirm anemia. The percentage of correct treatments was always high when the F values 4 and 5 were used as criteria for positive tests. For all the PCV cut-off values, more animals were classified as false positives when evaluated using F 3, 4, and 5 as criteria for a positive test and more true negative animals when evaluated using only F 4 and 5 as criteria for a positive test. For both sets of criteria for the positive tests, few animals were classified as false negatives and true positives. Eliminating the classification of F 3 as anemic decreased the sensitivity and increased the specificity for all the PCV cut-off values for the ewes. The F system can be used as a reliable alternative to reduce selection pressure for anthelmintics in relation to routine non-selective blanket treatment for worm control in the Morada Nova ewes.