Incidence of Mulberry Heart Disease (MHD), a condition of the heart muscle that often leads to sudden death, has become a growing concern in the pig population. Linked to oxidative imbalance, many in the pig industry point to changes in pig rations – particularly the increased use of DDGS (Distiller's Dried Grains with Solubles) and the threat of more concentrated levels of mycotoxins – as adding fuel to this culprit's fire.
By Lori Weaver
But with the economic benefits of using distillers grains for pig rations difficult to pass up, the days of feeding traditional corn and soy diets are unlikely to return to the extent seen in the past. Nonetheless, there are some
things today's pork producers can do to reduce the impact of this devastating disease on their herds without losing out on the economic benefits of feeding distillers grains.
In pigs, the genetic selection for fast growth and lean, muscular animals has been linked to an increased prevalence of metabolic diseases, including MHD. The condition is associated with cardiovascular inadequacy and also to oxidative stress.
Because weaned pigs rely heavily on fat-soluble vitamin E for healthy nervous, muscular, immune and circulatory systems during their period of fast growth, they are also the category most often at risk for displaying conditions associated with MHD. And while pigs receive nutrients from the sow while nursing, there is some evidence that vitamin E and selenium levels in sow's milk across the pig population has been slowly declining with the increased feeding of DDGS, contributing to oxidative imbalance.
Weaned pigs especially require a properly balanced diet to provide all necessary nutrients. While sufficient vitamin E was once a natural in the pig ration via staple ingredients like soybean oil, today's diets often fall short and some believe this contributes to stress and contributes to metabolic disorders such as MHD.
Once it gets a stronghold, the disease often attacks the heart muscle. A heart muscle that is stressed and not pumping correctly can result in heart failure. Fluid can collect around the heart, making it impossible for it to pump adequately and supply the pig's body with oxygen and other nutrients. Affected pigs often die suddenly or appear paralysed. MHD is often only diagnosed after a necropsy has been performed.
Causes of deficiency
With their fast growth rate, pigs are often more acutely affected by an improper balance of nutrients in the ration – such as inadequate levels of vitamin E – than other livestock.
The resulting metabolic diseases are indicators of oxidative imbalance. Oxidative imbalance arises when production of harmful free radical compounds exceeds the body's natural ability to detoxify them. This can occur in a number of ways. Increased free radical exposure by the pig may occur:
• As a result of the immune response,
• By increased absorption of free radicals from the diet,
• By an increase in metabolic rate such as that seen with increased growth rate, or
• As a result of the body needing to detoxify certain compounds, such as mycotoxins.
Likewise, oxidative imbalance can occur as a result of decreased intake or absorption of certain nutrients that aid in free radical detoxification. Traditional dietary management of free radicals has primarily been accomplished with the addition of vitamin E and selenium. These two nutrients work together to form a sort of 'free radical first line of defense'.
The two nutrients are closely related, with vitamin E status of the animal dependent on a supply of selenium for normal vitamin E recycling. Therefore, addition of vitamin E without necessary selenium may not be as effective at improving the long-term oxidative balance of the animal. Similarly, addition of selenium without vitamin E will not necessarily solve the problem.
A deficiency of vitamin E and selenium has been associated with MHD symptoms in suckling and weaned pigs in the past. Organic selenium has been used by the North American pork industry to improve the selenium status of offspring through increased selenium secretion in milk and subsequent increased selenium intake in the suckling pig, providing for the building up of selenium stores in tissues for the post-weaning period. Management of vitamin E levels, other than diet, can be further supplemented with vitamin E in the water during the post-weaning period. However, pigs that take more time to adapt to feed and water changes, often fall victim to post-weaning oxidative imbalance.
But new research out of Iowa raises additional questions as to the relationships among vitamin E, selenium and MHD. Dr Steve Ensley, DVM, clinical toxicologist, Veterinary Diagnostic Laboratory, Iowa State University, says he believes there has been an increase in MHD cases over the past two years, but clearly identifying why that has occurred is not so straightforward. He's been involved in a study designed to analyse pigs that have been diagnosed with MHD at the farm. Approximately 100 weaned pigs from ten sites were used in the study.
“We took tissues for microscopic exam, analysed liver and heart for vitamin E and calcium, phosphorus, potassium, magnesium, sodium, cadmium, cobalt, chromium, copper, iron, manganese, molybdenum, selenium and zinc, and looked for several infectious agents,” Ensley says.
The data are still being compiled and analysed, but Ensley hopes it will provide additional information on the relationship between MHD and vitamin E-selenium deficiency and insight into how best to meet the nutritional needs of pigs at risk.
Impact of DDGS
Feeding DDGS in pig rations has come about primarily due to ingredient costs. DDGS inclusion levels of 40% in gestation diets, 20% in lactation diets, and 30% or greater in growing-finishing diets are not uncommon.
However, as the implementation of increased levels of DDGS increases, reports of production challenges apparently associated with the change in ingredients used appear to be on the rise. Animal health and nutrition company Novus International reports that among the greatest concerns producers have raised over feeding an increased amount of DDGS is an increase in the incidence of MHD in offspring from sows fed high DDGS diets.
Why might this be the case? Evidence can be found in examination of one such production system feeding DDGS. The system was experiencing a number of serious problems with their weaned pigs when they fed DDGS to their breeding herd. In fact, the problems had become so severe that management was going to discontinue feeding DDGS despite a savings of approximately US$0.50 per weaned pig at the time. When DDGS was removed from the ration, the problems diminished. When it was returned to the diet, the problems reappeared. DDGS levels were approximately 20% in gestation and 10% in lactation.
To work toward a solution to the problem, milk samples were taken during late lactation from a group of sows that had received DDGS during both gestation and lactation. Then DDGS were removed from all diets for a period of about six weeks during gestation and these sows received a lactation diet without DDGS. A group of sows that had not received DDGS during late gestation or lactation were then milked. Sows were chosen for milk collection so as to match in parity as closely as possible the sows receiving DDGS from whom milk samples had been originally taken. Milk samples were frozen and analysed by Dr Don Mahan, Ohio State University, for milk selenium and tocopherol analysis.
Mahan's findings support the theory that inclusion of DDGS can lead to greater oxidative stress and thus, an increased incidence of MHD. Fifteen out of the 20 sows fed corn soy had milk selenium levels higher than the highest levels of milk selenium observed in the group of sows that were fed DDGS. The research results represent an effect of DDGS on selenium transfer through milk, most likely a result of decreased selenium absorption by the sow. It is thought that the sulfur content of the diet was likely a contributing factor in reduced levels of selenium.
In addition, milk tocopherol levels, an indication of vitamin E status, were lower in sows fed DDGS. Piglets consuming milk from mothers with lower milk tocopherol might be expected to be more susceptible to oxidative imbalance and thus susceptible to decreased performance both pre- and post-weaning.Oxidative imbalance with increased use of DDGS can also be affected by mycotoxins. While some products may be useful in restoring feed intake when mycotoxins such as aflatoxins are present, enough mycotoxins can still be absorbed to potentially upset oxidative balance which can then lead to negative health consequences for the animal. This suggests that the best mycotoxin management plan includes a product that minimises mycotoxin absorption in the first place, preferably in conjunction with a synthetic antioxidant blend that can improve vitamin E status.
Recurring problems with Mulberry Heart Disease can take their toll by way of lost pigs and lost gains as much as 7 kg per pig. While traditional diets can lead to problems with the disease, pig nutritionists are seeing increased incidence of the condition with greater percentage of dried distillers grains (DDGS) in pig rations.
While it's difficult to eliminate the possibility of MHD entirely, there is the opportunity to have greater control over higher incidences of the disease. Oxidation balance management is a good place to start. When feeding DDGS in the pig diet, total fat levels and poly unsaturated fatty acids are increased, specifically pro-inflammatory n-6 fatty acids. This causes an increase in the amount of unsaturated fat deposited and also the pig's susceptibility to cell membrane lipid peroxidation.
A related concern with the increased use of DDGS is that during ethanol fermentation, a portion of the corn oil may be converted to secondary oxidation products that can have an adverse effect on diet acceptance, as well as increase the oxidative load when consumed by the pig. Addressing the oxidative balance needs of your pigs may help you more successfully utilise DDGS as a valuable nutrient source, paving the way for lower feed costs.
Managing oxidative balance
Tackling a Mulberry Heart Disease issue in the pig herd begins with good oxidation balance management. Following these steps should help you continue to make use of DDGS in the pig diet while still keeping the incidence of this disease at bay:
• Support the pig's natural antioxidant system. • Reduce exposure of the pig to food-borne sources of oxidation products.• Preserve nutritional value of ingredients.
• Minimise immune system activation.
Source: Pig Progress Volume 26. No.1