There are many diseases in poultry production that cause substantial economic losses to the industry each year due to increased mortality or impaired growth. Colibacillosis caused by strains of E. coli organisms and avian salmonellosis, which includes a large group of acute or chronic diseases caused by Salmonella, are, in addition to many others, some of the most common causes for increased economic losses.

Given that bacterial diseases in poultry also affect humans, and that epidemiologists suggest that poultry meat is a primary factor in human food poisoning, authorities and poultry producers are increasing their focus on the control methods. Controlling these bacteria involves, among other things, improving monitoring systems, controlling the use of antibiotics, feed pelleting or improvements in management, and also maintaining high hygiene standards.

The most important physical parameters when it comes to the growth of microorganisms are pH, temperature and the presence or absence of moisture.

Growth of microorganisms is more likely to happen in a nutritious environment. A nutritious environment is found in animal feeds, especially in feeds for young animals, which are rich in nutrients to meet the requirements for high protein deposition in the early stages of growth.

The nutrients required by various bacteria differ. Bacteria require energy, nitrogen deriving from amino acids, urea ammonia, creatinine, methylamines, as well as vitamins and minerals, including phosphorus, iron, magnesium, sulfur, manganese, calcium and potassium. In general, it can be said that the more complex the diet, the better for microorganism growth, and the diets of young animals are usually more complex than those of older animals.

Additionally, the acidity or alkalinity of feed affects the growth of pathogenic bacteria and most bacteria prefer a neutral pH around 7 and will not grow at a pH below 4.5.

The ideal temperature for the bacterial growth is 30-45C. The body temperature of a newly hatched chicken is about 39.7C and they are usually kept at air temperatures of 30C and litter temperatures of 28-30C. Therefore, not only does the gastrointestinal tract of the young broiler provide an ideal temperature for the growth of bacteria, the environment does too.

Another factor needed for bacterial growth is moisture. Most feedstuffs contain sufficient moisture to provide the water bacteria need. Water activity measured in aw indicates how tightly water is bound in feedstuff. At an aw of 0.61 for example the growth of some bacteria is possible. At aw 0.90 most bacteria feel comfortable and the growth of bacteria such as Salmonella, E. coli or Listeria is most likely to occur. Furthermore, bird droppings may increase the moisture levels of the litter.

Management, hygiene – key to performance  

Bacteria are present everywhere in the environment. In an animal’s gastrointestinal tract, the bacterial flora will comprise pathogenic and beneficial bacteria.

The presence of pathogenic bacteria is not always a problem. However, in times of immune suppression or stress or when bacterial numbers increase, pathogenic bacteria can become problematic. Therefore, it is highly important to strengthen a bird’s defense mechanism and to keep pathogenic bacteria levels low in the environment and in the gastrointestinal tract. This can be achieved through management strategies, such as improving welfare and hygiene.

Good management includes not only making sure that welfare requirements are met, but also that nutritional needs are met. Welfare and nutrition are, in fact, in symbiotic.


Even when the nutritional requirements are met optimum growth will not be achieved, if welfare requirements are ignored. If all these factors are addressed, birds will be less susceptible to pathogenic bacteria and morbidity and mortality will be lower. However, as mentioned, hygiene plays an important role in maintaining a bird’s health and, therefore, optimum growth performance. As pathogenic bacteria are constantly present, only becoming a problem when their levels increase, a clean environment in which it is difficult for them to replicate needs to be maintained, to keep bacterial challenge for the birds as low as possible.

Organic acids  

The use of organic acids can help in water and feed hygiene. When organic acids dissociate, reduction of pH occurs due to the liberation of H+ ions. This reduction in pH leads to the creation of unfavorable conditions for pathogenic bacteria such as E. coli and Salmonella.

As shown in Figure 1, pH in drinking water was reduced from 7.31 to a pH of 4.38. The optimum pH for pathogenic bacteria is around 7, which means that water itself offers an ideal environment in which to grow. After adding a mixture of formic, propionic and lactic acid to the water, pH fell below 4.5, a level which impairs growth. This can be seen in Figure 2 in which the colony forming units per milliliter of water, with and without acid supplementation, is shown. By adding the mixture of formic, propionic and lactic acid to the drinking water, total microbes in CFU/ml drinking water were reduced from 6.5x105 to 1.4x105. Also in feed, a pH reduction from 5.4 to 4.5, 4.4, respectively, was found when adding a mixture of formic and propionic acid at an inclusion level of 3 and 5kg/t to feed, again creating unfavourable conditions for bacterial growth.

Why fight the challenge?  

Maintaining hygiene and reducing the bacterial load within feed is likely to result in improved growth performance. The lower the pathogen load in feed and water, the lower the intake by the bird in general.

However, a full elimination of pathogens is impossible, particularly during times in which birds are more susceptible to challenge, for example at a young age or during stress. In general, the host is competing with the bacteria for nutrients and a certain amount of energy, and other nutrients, such as amino acids, are lost to the microflora in the gastrointestinal tract. Furthermore, bacteria may secrete toxic compounds, decrease nutrient digestibility, and stimulate rapid turnover of absorptive epithelial cells. The presence of bacteria may also require an increased rate of mucus secretion by intestinal goblet cells and stimulate the immune system development and inflammatory responses. This all may result in impaired growth performance.

Fight pathogens effectively  

While organic acids may provide the opportunity to reduce the bacterial load in feed and water, and hence reduce the intake of pathogens by the animal, fighting pathogens is still a challenge. Even organic acids have a direct antimicrobial effect, as they penetrate the bacteria in their undissociated form and exert adverse effects within the bacterial cell, yet combating pathogenic bacteria is still difficult.

This is especially the case when it comes to Gram-negative bacteria as they have an additional outer membrane, providing them with an inherent protection against antimicrobial substances. However, this outer membrane can be damaged by so called permeabilizing substances. When permeabilizing substances weaken the outer membrane of Gram-negative bacteria, the activity of antimicrobials is increased. This leads to synergistic effects when a permeabilizing substance is added to a mixture of organic acids. Feeding such a mixture to broiler chicken has been shown to improve growth performance, as birds have to compete less with bacteria for nutrients and energy.