Diarrhea is the most common cause of morbidity and mortality in recently weaned piglets. The origins of diarrhea can be pathogenic, nutritional and even compounded through secondary complications. Pathogenic diarrheas require veterinary intervention to cure symptoms and eliminate the offending microorganisms. Nutritional diarrheas usually follow or proceed pathogenic ones, and thus, a combination of nutritional and medical interventions is often required. Obviously, a properly designed nutritional program by a qualified nutritionist should be able to prevent common nutritional diarrheas.
Nutritional diarrhea originates from three main faults in the design of a feeding program:
- First, diets that fail to initiate vigorous feed intake immediately post-weaning cause hunger, followed by over-eating when pigs associate dry feed with nourishment. Even short-term starvation is capable of diminishing the digestive and immune capabilities of the gastrointestinal system. Thus, when pigs over-eat after a period of malnutrition or starvation, digestion is incomplete, resulting in excess amounts of substrate (energy and protein) available for proliferation of opportunistic pathogenic microorganisms (e.g., Escherichia coli or Salmonella).
- Second, diets of relatively low quality, which are often used to reduce feed cost, not only discourage the development of an early appetite, but also their intrinsic low digestibility results in even more undigested material becoming available for bacterial proliferation in the lower gastrointestinal tract.
- Third, certain ingredients (e.g., soybean meal) contain anti-nutritional factors (e.g., storage proteins glycin and beta-conglycin) that may cause gastrointestinal inflammation when combined with a low-feed intake and impair the development of the gastrointestinal epithelium.
It is also suggested that diets with a high concentration of simple sugars and minerals may disturb the osmotic balance across the enteric epithelium, causing excessive water secretion in the lumen and loose stools. For instance, by changing the amount of sugars (sucrose and corn syrup solids), dietary osmolality was manipulated between 250 and 700 mOsm/kg. In that study, absorption of water and carbohydrates from the small intestine in piglets increased, and thus chances for diarrhea were minimized, as osmolality increased at similar dietary electrolyte balance. Osmotic diarrhea may not be detrimental to animal performance and health as pigs are able to compensate by drinking more water. Nevertheless, it is a disturbing sight for human operators, and it should be prevented, because it is rather difficult and expensive to differentiate from other forms of diarrhea.
Escherichia coli survey
Post-weaning Escherichia coli diarrhea has been long associated with low-digestibility diets, because undigested nutrients in the gut favor proliferation of pathogenic strains of Escherichia coli that cause over-secretion of intestinal fluids and electrolytes in the lumen of the gut. This invariably leads to diarrhea, malnutrition, poor growth and occasionally death. Results from a comprehensive survey in Canada including 34 commercial farms, of which 17 were reporting Escherichia coli problems, indicated that the majority of diarrhea incidents occurred between three and 10 days post-weaning. However, cases as late as 23 days post-weaning were not uncommon.
Moderate levels of functional fiber enhance movement of digesta through the gastrointestinal system, increase digesta water retention and facilitate defecation.
In farms where Escherichia coli diarrhea was prevalent in nursery pigs, diets were found to contain higher levels of vegetable protein sources (+12 percent), namely soybean meal and canola meal. Also, pigs that suffered from diarrhea were fed diets higher in calcium (+25 percent) and magnesium (+6 percent), both of which increase alkalinity in the gut (Escherichia coli thrives in alkaline conditions). Moreover, zinc oxide use was 21 percent less in diets for pigs that were reported suffering from diarrhea. Finally, electrolyte balance was relatively reduced in diets for scouring pigs (-8 percent). Although this study does not establish a clear cause-effect relationship between dietary composition and Escherichia coli diarrhea, it provides at least an indication that improper diet formulation can predispose pigs to diarrhea, intensify symptoms, or delay recovery.
Nutritional links to edema disease
Edema disease, a complicated enteric disorder caused by enterotoxemic Escherichia coli strains, continues to puzzle veterinarians and nutritionists regarding prevention and treatment of affected animals. A Dutch research group examined affected and healthy pigs from the same herd and concluded that although edema disease is closely associated with the presence of Escherichia coli (O139K82 strain in this case), dietary factors may also contribute or aggravate this intestinal disorder. Affected pigs exhibited symptoms of metabolic acidosis, evidenced by higher blood and intestinal acidity. The researchers speculated that toxins produced by Escherichia coli in the gastrointestinal tract may have a greater chance to cross the intestinal barrier in pigs suffering from metabolic acidosis because increased intestinal acidity is associated with enhanced permeability. Therefore, nutritional intervention strategies to reduce acidocis in the face of an edema disease outbreak may be beneficial. In addition, dietary immunoglobulins designed against edema-causing bacteria may be an additional strategy deserving to be taken into account when designing a special diet for such problems.
It should be emphasized that nutritional interventions after the onset of diarrhea should be made in consultation with the attending veterinarian and nutritionist. Because scientific experiments with infected pigs raised alongside healthy pigs in the same room are practically invalid, practical experience rather than scientific evidence is usually the basis for deriving most recommendations Farms experiencing high incidents of post-weaning diarrhea can follow one or more of the following measures:
- Prevention. For bacterial diarrheas, measures prescribed for antibiotic-free diets are equally applicable. For viral diarrheas, however, vaccination is most helpful, although antibacterial measures are strongly recommended to prevent secondary bacterial complications.
- Restricted feeding. This practice was particularly popular in Europe. Weaned pigs were offered a limited amount of feed during the first week post-weaning, with increasing allowances of feed until pigs attained ad libitum levels during the second week. The development of modern diets and later weaning age, along with the use of creep feeds and/or milk replacers have all but virtually made such practice impractical. In addition, a field study from Denmark where restricted feeding used to be the norm, revealed that restricted feeding may not always be as effective against diarrhea as previously thought.
- Reduced anti-nutritional factors. Soybeans and most legumes contain anti-nutritional compounds that have the potential of triggering the immature digestive immune system of the weaned piglet, with inflammation and diarrhea usually following ingestion of high doses of such anti-nutritional factors. Thermal processing of offending ingredients usually prevents intestinal inflammation, but in pigs suffering with severe diarrhea elimination of such ingredients is strongly recommended. Selecting the right source of soybean proteins remains crucial in modern piglet feed design.
Increased dietary bulkiness. Moderate levels of functional fiber enhance movement of digesta through the gastrointestinal system, increase digesta water retention and facilitate defecation. Addition of fiber in nursery diets is believed to increase excretion of pathogenic microorganisms, prevent attachment of bacteria to the enteric epithelium and establish a healthy gut. Rolled oats, sugar beet pulp, alfalfa meal, wood fiber and wheat bran are some of the most common sources of fiber being used today.
Feed quality issues. Ensuring that feedborne pathogens do not reach young pigs is a sound way of preventing unnecessary cases of diarrhea. To this end, ingredient selection is of paramount importance, as is a rigid quality assurance program. Finished complete feeds are often heat-treated to reduce bacterial load. For example, in Denmark, there is a requirement for all piglet pelleted feeds to be heated to at least 83 C. Recent evidence also suggests that a coarse feed texture and meal form is more protective against proliferation of Escherichia coli and Salmonella compared with finely ground or pelleted diets, although this is highly contestable among nutritionists and veterinarians.
Learn more: Fighting edema in piglets with nutrition