Absorption is the movement of nutrients across the lining of the alimentary tract. Most absorption of the nutrients in foods takes place in the small intestine. When food is eaten it usually needs to undergo a serious of chemical changes to break it down into it's constituent nutrients (proteins, fats, carbohydrates, vitamins, minerals and water) so that they can enter the body. These processes are called digestion and involve enzyme activity. Some food constituents , such as dietary fibre are not digested by the enzymes produced by simple stomached animals such as cats, dogs and humans, and so they are not able to be absorbed. However, in ruminants these fibres are broken down by bacterial fermentation in the rumen and then they can be absorbed.

Once broken down into smaller chemicals ( egs amino acids, fatty acids, peptides) nutrients are absorbed across the lining of the intestinal wall. This process can be passive (as with simple diffusion) or may involve active absorptive processes.

Any disorder that interferes with the absorption of nutrients from the gut lumen contributes to a failure of normal absorption - and this is called malabsorption.

Common causes of malabsorption include :

Small Intestine disease

• Inflammatory bowel disease (the most common cause)
• Chronic mucosal disease
• Drug toxicity - neomycin, kanamycin
• Causes of villus atrophy - histiocytic, eosinophilic, neutrophilic enteritis or lymphosarcoma
• Enzyme deficiency

Brush border enzyme deficiency - e.g. lactase deficiency in some animals

Breed Occurrence
German Shepherd Dogs are predisposed to develop eosinophilic enteritis and small intestine bacterial overgrowth - both of which cause malabsorption.

Irish Setters have been recorded to develop Gluten-sensitive enteropathy which results in malabsorption. 

Signs

Typical signs of the malabsorption of food include :

• Weight loss
• Diarrhoea 
• Steatorrhoea 
• Increased appetite - called polyphagia 
• Colitis 

Dietary Management
In malabsorption brush border enzymes disaccharidase concentrations are often significantly reduced (e.g. the enzymes maltase and lactase) so excess carbohydrate intake should be avoided. As these animals may have milk intolerance- milk and other lactose-containing products, such as yoghurt, should not be given

Treatment
Specific treatment depends upon the underlying cause (follow links above under causes)

Long term problems

Long term problems depend upon the underlying cause (follow links above under causes). The result of chronic malabsorption is poor nutrition, and undernourished animals are more susceptible to infections and are less well able to recover from disease.

Updated October 2013