Veterinary FAQs

What are the factors that upset the microflora and induce changes in the gut flora?

The use of antibiotics can adversely affect the gut flora.  When antibiotics are used, as a treatment for clinical disease, a proportion of the beneficial microorganisms becomes disrupted and can lead to an increased susceptibility of the gut to colonisation of pathogenic bacteria. The consequent reduction in disease resistance is manifested by an increased vulnerability to salmonella and other pathogens colonisation of the gut which may lead to diarrhoea.

One factor that should be considered when dealing with animals is stress. There is also strong evidence that stress can affect the composition of the gut microflora. Stress can be described as a factor that stimulates homeostatic, physiological and behavioural responses in excess of the norm. The only accepted measure of the presence or absence of a stressor is the blood level of adrenal corticosteroids which becomes raised during stress which effects the peristaltic movement of the gut and the production of mucus within the gut.  Stress also affects the intestinal microflora by reducing the concentration of lactobacilli and other Lactic Acid Bacteria (LAB) and increasing the concentrations of coliforms such as E. coli.

All stressful situations to which an animal is exposed contribute towards an increased intestine pH (more alkaline), and thus the gastrointestinal tract is likely to favour the development of pathogenic species such as E. coli at the expense of beneficial species.

Vaccination, antibiotic therapy, weaning, travel, rehoming or illness are a few of the factors that are considered as stresses that may result in a change of balance of gut flora in favour of pathogenic species.

Stress is also known to alter the protease content of saliva. As a result fibronectin and the autochthonous (commensal) bacterial population are lost from the oropharyngeal surface in stressed individuals. This autochthonous population is then rapidly replaced by a biofilm composed largely of Pseudomonas aeruginosa.

Stress can depress the immune response of animals and some antibiotics have been shown to depress the immune response significantly leading to a reduction in weights of the spleen and thymus. Withdrawal of the antibiotics in these cases can lead to the restoration of gut flora and a return to immune function. Antibiotics can also often reduce the lactobacilli population. Hence animals enduring stress exhibit alterations and breakdown of the regulatory mechanism in the gastrointestinal tract ecosystem allowing easier establishment of pathogens within the tract.