From birth, the piglet’s digestive system is geared towards processing milk-based fat, protein and carbohydrate. These are relatively simple molecules that the primitive gut can cope with. As the piglet grows, colonisation of the gut occurs with a wide range of microbes, most of which will originate from the sow. In the healthy piglet, there is a stable balance between helpful and harmful organisms in an environment that is influenced by the fact that the piglet eats a liquid diet of simple composition (milk) little and often.
When weaned, under conventional “crash” weaning systems, massive changes occur to the gut of the pig. The diet changes from liquid “on tap” to solid based, containing fat, protein and carbohydrate that will be vegetable based. Cooking of cereals and other processing will assist the digestibility and the inclusion of whey proteins and other milk products will offset the changes that the pig meets. The patterns of feeding may also change in that engorgement is more likely to occur “over-loading” the gut.
The stomach is acidic normally and acts not only to kill off potential harmful microbes entering with the food but to control the pH of the intestine, thus limiting microbial over-growth. There is a tendency for this effect to be lost or reduced post weaning, potentially allowing a gut environment more favourable to microbial growth.
Furthermore, the lining of the intestine consists of villi – microscopic finger like projections which vastly increase the surface area, allowing improved digestion and absorption of nutrients. In response to the stress of weaning and as a result of meeting foreign proteins, these villi shrink, reducing surface area and, hence, digestive and absorptive capacity. This will allow undigested food to pass further down the gut where microbial proliferation will occur causing scour.