Culture of strategically pooled bovine fecal samples as a method to screen herds for paratuberculosis

Fecal samples from 733 cows in 11 dairy herds with a low prevalence of paratuberculosis were cultured for the presence of Mycobacterium avium subsp. paratuberculosis both individually and after combining (pooling) in groups of 5. The culture procedure was the modified Jorgensen method, which uses NaOH and oxalic acid for decontamination and modified Lowenstein-Jensen agar slants for cultivation. Pooling was performed by mixing fecal samples from 5 animals ordered by age, herein referred to as strategic pooling. Culture of individual fecal samples detected M. a. paratuberculosis infections in 43 of the 733 cows and 7 of 11 infected herds (herd sensitivity = 64%). Culture of pooled fecal samples detected M. a. paratuberculosis in 28 of 151 pooled samples representing 8 of the infected 11 herds (herd sensitivity = 73%). Feces of the 43 culture-positive cows was included in 32 pools: of these 32 pools, 26 were culture positive and 6 were culture negative. In addition to the 26 positive pools containing feces from cows that were found culture positive on individual fecal samples, another 2 pools were culture positive, although comprised of feces from cows with negative results after culture of individual fecal samples. From the total of 45 infected cows that were found (43 by individual fecal culture and an additional 2 by pooled fecal culture), individual fecal culture detected 43 of these 45 (96%), while pooled fecal culture detected 39 (87%). Culture of strategically pooled fecal samples using the modified Jorgensen method was equivalent in herd sensitivity to the culture of individual fecal samples and is significantly less expensive.