Introduction. The distribution of MAP in tissues of cattle culled from known infected herds has not been well characterized especially relating the MAP tissue burden to previous fecal cultures over time. The objective of this project was to better correlate fecal shedding to MAP tissue bio-burden and to determine what proportion of fecal culture negative cows would have culture positive fecals and tissues at slaughter.

Materials and methods. Tissues and fecal samples were harvested from cows culled from 3 dairy herds. Samples were collected from a total of 174 animals. Five samples were collected from each animal; 2 intestinal lymph nodes, ileum, IC valve and a fecal sample. Fecal samples were process using the 3 day incubation method with HPC/BHI and tissues were processed using 2 day method in HPC. All samples were plated on solid media - Herrold's egg yolk with mycobactin J.

Discussion. Of the 174 cattle with harvested tissues, 17 (9.8%) were previously fecal culture positive for MAP. Fourteen of 17 animals were positive at slaughter (82%) and 3/17 (18%) cattle had all 5 samples culture negative. Each of these three cows with negative tissues was previously fecal culture positive with only one cfu of MAP on one of four tubes of HEYM. These three positive fecal samples may have represented transient "pass-through" MAP from other cattle in the herd.

Of the 20 fecal culture positive cattle at the time of slaughter, 9 were characterized as heavy shedders in the fecal samples with over 100 cfu MAP/tube and the same 9 cows massively infected in each of the four tissues examined with more than 300 cfu MAP/tube. No other fecal culture positive or negative cows had such massive tissue infection with MAP. Interestingly 5/20 (25%) fecal culture positive cows at slaughter had negative cultures on all four tissues. Three positive fecal culture cows (very low shedders) had only one colony on the four tissues cultured, suggesting infections as adults. The other 3 cows had modest levels of MAP in several tissues.

Of the 156 cattle with all negative fecal cultures prior to culling, 58/156 (37%) had at least one positive sample at slaughter. Of these 58 cattle, 25 were culture positive only on one sample, 11 on two samples, 12 on three samples, 6 and 4 samples and 4 cows positive on all five samples. An intestinal lnn was positive most frequently, followed closely by ileum and IC valve. 26/58 (45%) cattle had less than 10 total cfu of MAP on 20 tubes of HEYM for the five samples suggests a more recent infection. While 18/58 (31%) cattle had the next higher tissue level of MAP ranged between 10 and 100 total cfu MAP for the 20 tubes, suggesting a heavier and or repeated doses over time as adults.

Conclusions. Cattle shedding more than a few colonies of MAP or had multiple positive fecal cultures had multiple tissues positive at high MAP concentrations. An estimated 35% of always culture negative cattle will have positive tissues at slaughter with a wide spectrum of MAP concentrations suggesting a moderate level of adult infections.

Acknowledgement: Financial support for this work was provided by a cooperative USDA Agricultural Research Service (58-1265-3-115) grant.