When looking at a bird’s digestion, this obviously starts at the beak where salivary glands begin the digestion process. Feed then descends into the crop via the esophagus, with the crop acting as an expandable storage component. Feed then passes into the proventriculus where digestive enzymes are released and then into the gizzard which is effectively a muscular stomach for mechanical breakdown.
The small intestine consists of the duodenum, jejunum and ileum where nutrients are absorbed. The lower intestine absorbs water and uses bacteria to help digestion, with the caeca helping with fermentation of undigested feed.
Any remaining products pass through the cloaca and are excreted.
The microbiome of the gut
The digestion and absorption process involves a whole network of different mechanisms and components that require specific conditions in the gut to work effectively. In addition, the bird uses microorganisms to help with digestion.
For scale, it’s predicted that over 50% of cells in the chicken at any one time are bacteria. Multiply that by 100 and that will be the number of viruses present.
This population of bacteria, viruses and other microorganisms is referred to as the microbiome of the gut.
The microorganisms that make up the microbiome of the gut are initially transferred from the hen and subsequently the environment in the first few days of life. In the hatchery the birds will receive probiotics – good live bacteria – to help with colonisation in the gut.
The difference to a good or bad crop
The beneficial gut microbiome, consisting of a complex mixture of good bacteria including lactobacilli and peptidococcus species, will promote digestion and growth rates and develop the immune system.
An increase in bad bacteria like salmonellas, E. coli and some clostridium species, will decrease growth rates, cause disease, and impede bird welfare.
In summary, a good microbiome can be the difference between a very poor and a very good crop. When the microbiome on site shift in the poor direction, either due to a potential pathogenic cause or environmental issue, it can be difficult to reverse, often resulting in a number of consecutive poor crops.
The important role of acidity in the gut
Acidity plays an important role in the gut. A pH of 7 is neutral, 1 very acidic and 14 very alkaline however that scale isn’t proportional. For example, a pH of 4 will be 10 times as acidic as a pH of 5.
The top part of the gut in the proventriculus and the gizzard is naturally acidic. The lower part is naturally neutral, if not slightly alkaline. Most bacteria can be found in the lower part of the gut in the alkaline conditions. And this is where organic acids have an impact.
A normal acid will not reach the lower part of the gut as it will lose its acidic properties in the face of a weak alkaline environment. By using a buffered acid, the acidic properties remain unaffected and will reach the bacteria in the lower part of the gut.
The bad bacteria will actively try to remove this acidity, until it runs out of energy. When this happens, the bad bacteria will die or at least have reduced viability. Conversely, the good bacteria prefer the acidic environment and will thrive.