Mulberry heart disease (MHD) in swine usually manifests as sudden death in young, fast-growing, apparently healthy pigs. The hallmark lesions are acute hemorrhagic myocarditis and myocardial necrosis resulting in heart failure. To clarify ongoing and recently increased questions concerning the etiology of MHD, we investigated the relationship between MHD and vitamin E, selenium, and 13 other mineral levels in heart and liver tissues. Additionally, several PCR assays were conducted on heart tissues to explore a possible relationship between viral pathogens and MHD. Samples were collected from a total 114 pigs representing a total of 45 farms with a known history of increased numbers of mulberry heart disease (MHD) in nursery pigs with 1-10% of the pigs affected by sudden death and gross lesions of MHD (enlarged heart with intramural hemorrhages, ascites, enlarged liver). The samples were collected from clinically affected and unaffected pigs ranging from 7 to 120 days of age. Depending on the type of samples collected, tissues went for either chemical analysis, pathogen analysis or both. On the basis of histological examination samples were separated into MHD and unaffected classifications. Of the 114 pigs, 75 liver and heart tissues were used for the chemical analysis and 66 heart tissues were used for the pathogen analysis. Among MHD and unaffected pigs, significant differences (P < 0.05) were observed in levels for sodium and copper in heart tissues and sodium and magnesium, in liver tissues. There was a significant (P < 0.05) difference in levels of selenium (0.73±0.05 for MHD; 1.15±0.11 for unaffected pigs) in liver tissue only; however, levels were still within the normal range. In heart tissues the mean ± SE selenium level was almost identical (0.48±0.03 MHD; 0.48±0.02 unaffected pigs). Due to supplementation of vitamin E in feed rations, 22 pigs with levels of vitamin E above 3.5 IU/kg were removed from the heart tissue analysis and 13 pigs were removed from the liver analysis. There was no significant difference found in levels of vitamin E in MHD and unaffected pigs in heart or liver tissues. Analysis of feed samples for selenium revealed that of the 22 samples tested all were above the 0.3 ppm legal supplementation limit for swine feeds. Vitamin E levels while not regulated were all above 20 IU/Kg with one sample reaching 340 IU/Kg.A total of 19 pigs were positive for PCV2 (9 unaffected; 10 MHD), four were positive for the North American PRRSV strain (3 unaffected; 1 MHD), 13 were positive for pan-herpesvirus (6 unaffected; 7 MHD), 8 were positive for porcine enterovirus (2 unaffected; 6 MHD), 1 pig was positive for PPV (1 unaffected), there were no positive pigs for any of the other pathogens tested.
There was an association of MHD with selenium levels; however, due to supplementation animals are no longer deficient in selenium, no other mineral or vitamin E associations can be made from this study. While many of the pathogens were isolated from several pigs among the groups, they did not appear to be associated with the MHD status in the pigs.