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.