Mulberry heart disease makes a comeback
Wednesday, October 6, 2010
Once virtually pushed aside as a major disease in pigs, MHD is now resurgent and indications are that distillers dried grains with solubles may be the culprit
by S. ERNEST SANFORD
Over the last 18 to 24 months I've been hearing of a growing number of outbreaks of mulberry heart disease (MHD). Reports are mainly from locations in the United States, but more recently also from Canadian sources.
MHD was very common in herds throughout the major pig-rearing areas worldwide in the 1960s and '70s. By the 1980s, researchers had nailed down the cause of MHD as being due to vitamin E and selenium deficiency, and these two micronutrients were widely incorporated into pigs' rations.
The results were so dramatic that, by the end of the 1980s, MHD had virtually been pushed aside as a major disease in pigs and was on the verge of being categorized as a "disease of antiquity." We thought we had this one licked and moved on to solving other riddles, like PRRS.
As many of our younger folk might not know of or have ever seen MHD, here is a quick review. It typically occurs soon after weaning, causing sudden death of the biggest, fastest growing, most robust-looking pigs. On postmortem examination, the heart is seen sitting in the pericardial sac, which is filled with bloody fluid and fibrin. Large paintbrush hemorrhages are seen on the surface of the heart and penetrating through the entire width of the heart wall. The abdominal cavity is also filled with fluid.
Vitamin E and selenium deficiency was identified several decades ago as the main factor precipitating MHD. Vitamin E and selenium are antioxidants that work to protect cell membranes from damage by toxic radicals that build up through metabolic processes.
Fast-growing pigs with increased metabolic rates outstrip the protective properties of these antioxidants, resulting in the catastrophic destruction seen soon after weaning.
Once the deficiency of vitamin E and selenium was identified as the cause of MHD, nutritionists very quickly incorporated supplementary amounts into sow and piglet rations. This done, most of the MHD problems we saw in the 1960s, '70s and early '80s virtually disappeared by the mid-to-late 1980s.
Fast forward to the last two or three years. Why are we now seeing a resurgence of MHD? What has changed?
Initial reports indicated that iron toxicity from injectable iron might be contributing to these new MHD cases. There was some movement to reduce the amount of iron injected into baby pigs from 200 to 100 milligrams, with some success in a few herds. But this success was restricted to only a few herds, probably related to certain specific genetic lines of pigs.
New corn harvested in the fall was the next item to come under suspicion. This connection between new corn in the fall and outbreaks of MHD was reported in a few Midwest U.S. herds. Reports indicated the outbreaks ceased when old corn was substituted for the new or when old corn was mixed with the new.
The one causative factor coming to the fore, however, has been the link between incorporation of high levels of DDGS (distillers dried grains with solubles) into sow rations and the precipitation of MHD in pigs that had suckled sows fed the high levels of DDGS. Levels being reported associated with MHD run as high as 40-50 per cent incorporated into gestating and lactating sow diets.
Observational field tests have succeeded in demonstrating that, when DDGS are taken out of the sows' rations, the MHD problem disappears. Put them back in at the 40-50 per cent level and – bingo! – MHD is back.
More controlled studies will have to be done to corroborate these field observations, but I think we might be on to something new here. The exact mechanism is, of course, unknown at this time, but that will come once researchers start unravelling this new problem.
At the recently completed 21st IPVS Congress in Vancouver, a Dutch researcher pointed out that, many years ago, they identified high levels of certain proteins in pigs' diets as contributing to MHD. Exact mechanisms were not specified.
I discussed with him our current observations of a link between DDGS fed to sows and MHD cases seen in their piglets. No definitive proof, of course, but he agreed that it was tempting to speculate that the high levels of protein in DDGS might be triggering the increase in MHD cases being seen currently. BP
S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com