Edema, or oedema, disease is a complicated yet quite frequent gastrointestinal disorder affecting millions of piglets each year.
Major symptoms include disorders of the nervous system, puffy eyelids, sometimes diarrheas, lameness, loss of appetite, depressed performance, poor overall condition, and of course, elevated mortality.
The best advice that could be offered is veterinary intervention and a high level of health status throughout all farm operations. Nevertheless, even under the best veterinary and management care, edema still emerges in certain farms. In these persistent cases, a number of nutritional intervention strategies are available to at least alleviate the symptoms of this disease, if not completely prevent or cure it.
It must be emphasized here that not all such nutritional strategies work in every farm, so their employment should be considered as part of a greater overall program against edema.
As edema diseased is thought to be triggered by certain serotypes of Escherichia coli bacteria, any dietary measure effective against normal colibacteria (causing piglet diarrhea) are usually effective against serotypes causing edema disease.
Edema disease is more prevalent in areas of the world where antibiotics and other antimicrobial agents are restricted in their use.
For example, piglets imported from southern Denmark to be finished in northern Germany (literally a cross-border transfer) are almost invariably without any symptoms. But, they quickly break down with edema disease once in Germany, something not mirrored in Denmark when similar pigs are transferred to finishing facilities there.
This has been attributed by many field experts to the lack of zinc oxide in German piglet diets, due to a ban of this ingredient. Thus, where allowed, zinc oxide is considered a good supplement to be used against edema disease. Usually, 3,000 parts per million of Zn are considered adequate to treat Escherichia coli infections.
In a recent study in Denmark, 27 isolates of E coli O139, which triggered edema, were evaluated against their resistance to well-known antibiotics. All 27 isolates were sensitive to colistin, gentamicin, apramycin and amoxicillin/clavulanic acid. Resistance to sulphonamide was found in 80% of the isolates.
Clearly, in many areas of the world where antibiotics are still allowed, their use greatly helps against the occasional flare up of edema. The correct antibiotic to be used should be left at the discretion of the attending veterinarian.
Most pathogenic bacteria, including E coli, feed on protein and, it makes sense to offer them less of a substrate to proliferate. To this end, the dietary protein level in diets for piglets suffering from edema disease should be lowered by 2-4 percentage points, while rebalancing the amino acid profile. To the same effect, increasing dietary protein digestibility also helps reduce undigested protein reaching the hind gut. The use of crystalline amino acids and highly digestible protein sources greatly help in this direction.
Alternatively, a lower-density diet may be offered, but this might also result in depressed performance due to lack of nutrients for growth and development. In this case, the least worst case scenario should be weighed against financial losses.
Apart from zinc oxide, copper sulfate, if and where still allowed, up to 250 ppm of Cu in the complete feed is also beneficial against bacterial infections, especially during the later stages of the nursery period.
It has also been shown that reducing the amount of calcium in the diet (for example a maximum of 0.8% Ca in the first post-weaning diet is recommended) improves stomach pH conditions, creating a less favorable environment for bacterial growth. Finally, it is important to keep in mind that E coli thrive on an iron-rich substrate, and it might be beneficial to limit this nutrient to minimal levels required for growth.
It is quite widely accepted that reducing or removing soybean meal from piglet diets greatly reduces the incidence of gastrointestinal disorders, including edema disease.
Although replacing soybean meal with other more digestible protein sources markedly increases feed cost, this is strongly recommended in the case of piglets suffering from edema disease. Organic acids, and perhaps some plant extracts, are also quite helpful against bacteria as they tend to create an environment unsuitable for bacterial growth throughout the gastrointestinal tract, and especially in the stomach. Blends of organic acids with or without plant extracts are usually better than straight acids.
Dutch researchers recently examined affected and healthy pigs from the same herd and concluded that although edema disease is closely associated with the presence of E coli, dietary factors usually contribute or aggravate this disorder.
Affected pigs in this study exhibited symptoms of metabolic acidosis, evidenced by higher blood and intestinal acidity. It was speculated that toxins produced by E coli in the gastrointestinal tract had a greater chance to cross the intestinal barrier in pigs suffering from metabolic acidosis, because increased intestinal acidity is associated with increased permeability. Therefore, nutritional intervention strategies in the face of an edema disease outbreak may be beneficial. The optimal dietary electrolyte balance (Na+K-Cl) for diseased piglets may be different than that for healthy piglets, because a higher dietary electrolyte balance may prevent metabolic acidosis.
Beyond the obvious suggestion of enhancing biosecurity, sanitation, and overall animal housing conditions, there are a couple of less known strategies for fighting edema disease.
First, limiting feed intake during the first four-five days post-weaning is strongly advocated in cases of high infective stress as this strategy reduces the amount of undigested feed reaching the hind gut. Also, the use of coarsely ground cereals instead of fine ones, and only uncooked, has been shown to further increase the overall health of the digestive tract in cases of severe bacterial infections. In addition, feed in meal form is preferable to pelleted feed when pigs are known to suffer from enteric diseases. Although these intervention strategies are quite effective in controlling gastrointestinal disorders, they also have the potential of limiting animal performance, and as such they should be employed with care.
Fiber Based on empirical evidence, increasing dietary crude fiber by 2-3 percentage points has been shown to help against many types of bacterial infections. To increase dietary fiber, barley and oats, often just coarsely ground, are quite effective while being more nutritive than other sources of fiber. Similarly, beet pulp has been effective in many cases, but not always, for unknown reasons. Other sources of purified fibers have shown mixed results so far, but research is ongoing in this area.
This is the latest method of addressing edema disease and it is, in fact, the only direct intervention method. Immunoglobulins are obtained from eggs that have been produced by hens hyper-immunized against strains of piglet-specific strains of E coli known to trigger edema disease.
These immunoglobulins are then added directly in the piglet feed and once ingested reach the gastrointestinal tract. There, they bind to the specific strains of colibacteria for which they have been produced, rendering them ineffective.
A recent trial evaluated the use of egg immunoglobulins on a farm with strong problems of edema disease. Results (Figure 1) suggested that pigs fed with egg immunoglobulins specific against edema disease were about 2.5 kg heavier at 68 days post-weaning, while mortality was just above 5% compared to 10% in piglets fed diets without this supplement. Furthermore, treatment cost for medicines was significantly reduced.