Practical dietary manipulation of the immune system for optimal field performance and body composition of poultry, and the use of probiotics in commercial poultry production, were among the topics of interest at this year’s World Nutrition Forum. The event, which took place in Salzburg, Austria, was no less spectacular than those of previous years, and not only offered an broad learning opportunity, but a great opportunity to meet experts and producers from around the world.
Alfonso Mirelles Jr, of Foster Farms, Delhi, US, reminded delegates that it is sometimes forgotten that nutrients are needed for both accretion and maintenance, and that the requirements for maintenance are much higher than those for growth.
Because nutrient requirements for growth are relatively minimal compared to maintenance, nutritionists need to concentrate on meeting and minimizing maintenance requirements, he suggested.
When formulating in the field, all nutritionists have minimum nutrient requirements for each stage of production. Furthermore, most have safety margins for all the nutrients in poultry diets, so in practice, the probability of not meeting all nutrient requirements for commercial flocks should be practically zero. Yet it is not unusual to find significant differences in performance among commercial flocks.
Stress as an immune response
Stress is dynamic, complex and metabolically it is the sum of the innate and adaptive mechanisms of an immune response. Immunity may be affected by nutrition and so, stress, in the form of an immune response, may at least be partially regulated internally.
From a nutritional point of view, activation of all immunity is relatively inconsequential. Although the immune system requires proper care and feeding, nutrient requirements for mounting an immune response, such as the production of immune proteins, activation, differentiation, and proliferation of immune cells does not require supplementation with additional nutrients.
The consequences of triggering an innate response, however, have huge implications in animal nutrition. More specifically, activating the acute phase response, which is the cornerstone of nonspecific immunity, releases a cascade of catabolic reactions, including degradation of skeletal muscle, a negative nitrogen balance, and repartitioning of minerals, vitamins and energy sources. This economically undesirable inflammatory reaction, however, is essential to mount an effective immune defense. The nutritional objective, therefore, should not be to eliminate it but to minimize it.
At its simplest, the acute phase response involves a triggering stress, such as a disease challenge, changes in environmental temperatures, handling, vaccination, and high stocking density. An acute phase response often triggers a secondary acute phase response, particularly in the digestive system. It is this secondary systemic response that is often targeted for intervention through the use of feed additives.
Once the inflammatory response has been triggered, there is activation of immune cells. Immune cells produce messenger proteins collectively called cytokines. Thus, normal cytokine profiles change and lead to secondary systemic responses. There is also an almost immediate adaption of organs such as the liver and spleen.
From a nutritionist point of view, it is these secondary systemic responses that are the most damaging economically, and an acute phase response needs to be minimized to maintain body weight, body composition, and ideal feed conversion. Physiocatabolic reactions need be down regulated to minimize losses of nutrients that have already been digested, absorbed and deposited.
Increasing immune resilience
In commercial poultry production, increasing resilience has been achieved through breed selection, use of additives and nutrient composition that helps birds to ignore and recover from stress. In poultry management, stress factors such as handling, sudden environmental changes and vaccine and disease challenges are minimized. Any treatment that prevents or minimizes stress translates into growth promotion.
When feed additives are tested with the concept of resilience in mind, it becomes clear that there are significant metabolic changes occurring that go beyond weight gain and feed conversion. There are physiological processes impacted with the use of dietary growth promoters that go beyond the effect of growth promoters in the digestive tract.
Stress, in the form of immune response, is an example of how allocation of limited resources can be shifted. Current research suggests nutrients play a much greater role in regulating an immune response than previously thought. Nutritionists, therefore, need to supplement their training beyond classical education so that they are able to modulate metabolic processes through the diet. Nutritional immunoregulation will play a critical role in the poultry industry in the future.
David J Caldwell, associate professor at Texas A&M University, looked at the use of probiotics in commercial poultry for efficient performance and enteric health.
Probiotics are naturally occurring bacteria, or a combination of different types of bacteria, that possess the potential to improve intestinal or gut health.
The ability of bacteria to colonise the gastrointestinal tract is dependent on:
- Bacterial factors that permit the organism to survive in the gastrointestinal environment;
- Host resistance factors which mitigate against maintenance of colonization by enteropathogens; and
- Interactions of the colonizing enteropathogens with indigenous normal microflora that compete with, or in some manner, inhibit the ability of a given enteropathogen to survive within the gastrointestinal tract.
Colonising organisms must be able to exploit a specific niche within the host, and therefore it may be possible to devise new control methods through understanding pathogen bacterial factors involved in colonization, he suggested.
An emerging area of interest related to broiler enteric health involves feeding probiotics to stimulate mucosal immunity and improve intestinal health. In commericial poultry, maintaining a healthy gut mucosa represents an essential first-step in protection against invading pathogens and dietary antigens.
Some enteric disease conditions, including coccidiosis, have major implication on performance and enteric health, and several investigations have demonstrated protection against Eimeria acervulina infections in chickens when given a preventative treatment of probiotic bacteria.
Probiotic bacteria have often been suggested as a natural control method for coccidiosis. Using them in this way can be seen as attractive, as modulating host responses would be considered more acceptable by consumers in comparison to prophylactic drug use.
Gut mucosal surfaces play a key role in the exclusion and elimination of potentially harmful dietary antigens and enteric microorganisms, and feeding probiotics to poultry has been shown to maintain beneficial intestinal microflora and may modulate the mucosal immune system. The colonization of mucosal surfaces by commensal bacteria can stimulate mucosal immunity during times of enteric pathogen invasion, thereby increasing the host’s resistance to the invading pathogen.
Intestinal pathogens can be detected and destroyed by the host immune system more effectively because a balanced and healthy microbial population could allow for the intestinal immunological defense mechanisms to achieve optimum performance, resulting in a more functional and timely immune system.
If a balanced microbial population is achieved, intestinal immunological defense mechanisms are allowed to achieve optimum performance resulting in a better control of intestinal pathogens.
Broilers are only reared to an age ranging from six to nine weeks. As such, there is often insufficient time to develop an extremely efficient immune response to many types of pathogen.
Through early immunostimulation, feeding probiotics to broilers could be an alternative method of enhancing the host resistance to enteric pathogens by creating a more responsive and developed immune system.
As traditional chemotherapy and dietary drug inclusion continues to become less commonplace in commercially reared poultry, probiotics and other natural additives are likely to be integrally involved in production programs. Probiotic supplementation represents a potential natural program for disease control and maintenance of a healthy digestive tract.
Alfonso Mirelles Jr reminded delegates that nutrients are needed for both accretion and maintenance, and that maintenance requirements are much higher than those for growth.