Neonatal diarrhea – a challenging condition affecting new-born piglets that every farrowing manager is familiar with. It is one of the most common symptoms of disease in the baby pig and the cause for this diarrhea is usually considered to be of infectious nature. However, it can also be associated with the pig itself and its environment.

Diarrhea in piglets is characterised by loose, watery faeces (with moisture levels higher than 80%), which have a higher frequency than normal. Diarrhea is also associated with abnormal intestinal secretion, higher intestinal permeability, motility disorders, resulting in impaired nutrient absorption. Diarrhea will therefore result in a quick loss of water, electrolytes, and nutrients affecting the vitality of the piglet and eventually leading to death.

Piglets, and especially those of low birth weight, are born with an immature intestine which has the potential to continue developing in the first days of life. Research has shown that already after 24 hours of life, the weight of the small intestine has a potential to increase by more than 50% while the large intestine can grow from 30-40%. The surface area of a piglet’s small intestine can double by the time they reach ten days old, and the number of enterocyte cells (absorptive cells that line the villi of the small intestine) can double in the first three days. This growth requires substantial amounts of the right nutrition and energy, especially from colostrum, that are not always available from the sow in modern production systems. Another important function of colostrum is to provide the piglet with passive immunity through molecules such as immunoglobulins. This is essential, because the piglet is born immunologically immature, since during gestation, the placenta does not allow the passage of maternal antibodies. Furthermore, even if the immunity cells and the gastrointestinal associated lymphoid tissue (GALT) are present at birth, it will take one to two months before the intestinal immunity is fully functional.

Because the immunoglobulins from colostrum need to reach the small intestine intact, the production of hydrochloric acid in the stomach is reduced in early age. Also, the colostrum has a buffering effect which ensures that the immunoglobulins are not damaged by the acidity. The activity of protein-degrading enzymes is also reduced (chymosin, the main protease after birth, is less active than pepsin which will become dominant later) and colostrum contains trypsin-inhibitors which favour the absorption of immunoglobulins. The downside of this protection of the immunoglobulins at the intestinal level is that such conditions will also stimulate the growth of pathogenic bacteria and possibly inhibit the degradation of toxic substances such as clostridial toxins.

Additionally, the low birth weight of new-born piglets, their limited capacity for thermoregulation leading to hypothermia, their low energy reserves, the lack of brown adipose tissue, and adverse environmental conditions are other factors that will promote the onset of neonatal diarrhea.

Although the term ‘neonatal’ is sometimes used to describe the entire period from birth to weaning, here we will consider as “neonatal diarrhea” the diarrhea observed during the first week of life. As described by various publications, diarrhea in new-born pigs is often triggered by a single pathogen. Neonatal diarrhea caused by a combination of pathogens are less common.

Pathogens causing neonatal diarrhea have different modes of action. Some have a negative impact on ion transports and barrier functions, some promote inflammation and loss of absorptive surface. Some bacteria such as enterotoxigenic E. coli (ETEC) cause severe diarrhea because the enterotoxins that they secrete will cause a hyper-secretory state in the intestine. Another pathogen involved in neonatal diarrhoea is Clostridium perfringens type C which causes damage to the intestinal mucosa, negatively affecting the absorption of nutrients, and resulting in loss of fluid and blood which are moving into the intestine. Damage of the intestinal epithelium, and therefore poor absorption of nutrients, are caused by rotavirus, or Cystoisospora suis.

In the next articles, we will discuss the main pathogens causing neonatal diarrhea, starting with Enterotoxigenic Escherichia coli and Clostridium perfringens type C. If you would like to read the rest of the series, please find part two here, part three here and part four here.