Low Sensitivity of FAMACHA© in Growing Lambs

Brazilian researchers conducted a study to determine the sensitivity and specificity of the FAMACHA© system in growing lambs. Between 2015 and 2016, lambs aged 60–210 days on two sheep farms were evaluated at 15-day intervals using the FAMACHA© system. In total, 1591 assessments were analyzed. The highest percentage of larvae in the fecal cultures was for Haemonchus spp., (Ht) with an average of 78.5%.

The sensitivity and specificity of the system were calculated according to two criteria: criterion 1, lambs classified as F4 or F5 were considered anemic (positive test) and those classified as F1, F2, or F3 were considered not anemic (negative test); and criterion 2, lambs classified as F3, F4, or F5 were considered anemic (positive test) and those classified as F1 and F2 were considered not anemic (negative test). Three gold standard Ht cutoff values were used to diagnose anemia, i.e., ≤22%, ≤18%, and ≤15%.

The sensitivity values found when F3 lambs were considered anemic were 13.9%, 30.8%, and 66.7%, respectively, for Ht cutoff values of ≤22%, ≤18%, and ≤15%. When F3 lambs were excluded, the maximum sensitivity was 14.9% and the specificity was 100% for all degrees of anemia using criterion 1. The FAMACHA© system had low sensitivity in growing lambs and should not be used alone for control of haemonchosis in young animals.

Source: Veterinary Parasitology February 2018.