Health through nutrition
As disease control options become more limited, proper consideration of nutrition is gaining in importance.
Maintaining poultry health is a challenge that is increasingly being addressed through nutrition. Knowledge of nutrition's role in health has expanded with new strategy development boosted by in-feed antibiotic bans.
Delegates at Alltech and Biomin-organised conferences held late last year were party to developments in the role that nutrition can play in protecting flock health.
Steve R Collett, of the Poultry Diagnostic and Research Center, University of Georgia, explained that raising broilers in close confinement without antibiotic growth promoters favours gastrointestinal inhabitants that can rapidly multiply.
The goal of any poultry operation is to economically convert feed into food, so it is critical to manage the risk and the consequences of disease challenges.
Disease in a flock becomes significant when the functional derangement of normal metabolic and homeostatic processes causes a large decline in productivity to affect economic efficiency. This occurs either because of disease-induced anorexia or through specific effects on the physiological processes of nutrient metabolism, respiration and excretion.
In contrast to respiratory disease, where early signs are outwardly apparent and easy to detect, low-grade gastrointestinal disease is more insidious. Birds eat and drink as "normal" even when the disease is quite advanced.
Dr Collett said current health monitoring systems focus on coccidiosis lesion scoring and are not sensitive enough to detect early changes in intestinal integrity. Yet microscopic changes in the intestinal lining can significantly hurt feed-conversion efficiency.
The composition of the intestinal microbiota today is likely a reflection of centuries of group selection. This is accelerated by breeding and selection programmes and in-feed antimicrobial use at broiler level, making changes difficult.
Progress in selection for favourable microbial communities is, however, possible over time since group-selection pressures on microbial communities are high when they are transferred to a new habitat. Provided pathogens are minimised in the microbiota, they are purged at flock depletion, house clean-out and placement. The gut microbiota can be improved, with each intervention providing incremental gain.
The downstream effects of compromised digestion and absorption can also be countered by improving nutrient availability and/or reducing the nutrient density of the diet. Exogenous enzyme addition to diets with corresponding reduction in nutrient density helps to avert the negative impact of malassimilation on microbiota diversity.
To cope without traditional chemoprophylaxis, alternatives need to be explored, Dr Collett recommended. Many gastrointestinal diseases are multifactorial and involve subtle shifts in intestinal microbial populations making eradication impractical or impossible.
Brooke D Humphry of the Department of Animal and Avian Sciences, University of Maryland College Park, explained that activation of the immune system results in behavioural and physiological changes associated with pathogen removal.
Many of these changes limit a bird's ability to achieve its genetic potential. While a bird needs to resist disease, fall in performance is the trade-off associated with immune activation. Minimising this is one way of improving efficiency and welfare.
Nutrition helps to achieve this. The immune system requires nutrients at appropriate times and in appropriate amounts to ensure proper development, maintenance and function.
When formulating optimal diets for the immune system, the type of nutrition offered must be considered, i.e. supply, and to which specific aspect of the immune system they are intended, i.e. demand — considering supply only can result in no impact on immune function or even decreased overall health. Nutritional approaches to enhance immune function should focus on supplying nutrients that complement the "pull" associated with increased nutrient partitioning for immune function.
Feeding probiotics and prebiotics results in improved gut health and increased enteric and systemic immune responses to specific pathogens. Although the exact mechanisms of how they alter immunity is unclear, their use can improve humoral, cellular and innate immunity.
Sensing friend or foe is a continuous challenge for the intestinal tract, pointed out Richard Ducatelle, of Ghent University. However, several bacterial strains present in the gut have beneficial effects on intestinal health and improve balance. These are generally called probiotics.
Numerous feed additives have been designed to improve digestibility and compensate for "anti-nutritional factors" in feed. It is becoming clearer that poor digestibility and anti-nutritional factors act, in part, by inducing a subclinical inflammatory response in the intestinal mucosa.
Feeding certain probiotics has yielded promising results in the treatment of inflammation diseases in the gut and other organ systems.
The future for improving gut health through feed additives lies in quorum sensing like molecules that are perceived by beneficial microbiota as positive signals and by harmful bacteria as a stop signal.
Coated butyric acid could be considered as a pioneer compound, since in concentration below the minimum inhibitory concentration value, it can suppress salmonella's major virulence mechanisms. Butyric acid can help protect chicken enterocytes from Campylobacter invasion and decrease the severity of necrotic enteritis caused by Clostridium perfringens in an experimental set-up.
Stimulation of the butyric acid producing microbiota using feed composition alterations or feed additives would increase gut wall integrity and stimulate epithelial cell growth, and thus improve performance while at the same time controlling pathogens.
Ilias Giannenas, of the Laboratory of Animal Nutrition and Husbandry, University of Thessaly, explained that among alternatives to in feed antibiotics, aromatic plants, herbal extracts and essential oils have a predominant place. Only in the last 20-30 years have scientists seriously begun to determine whether plant derived traditional remedies are effective.
Aromatic plants and their extracts have been found to exhibit antimicrobial and antiparasitic activity, and to possess antiviral and antioxidative affects. Herbs and their metabolites also stimulate the immune system.
The effects of aromatic plants and their extracts on chickens life and growth performance are highly variable, however, possibly due to their effects not only on the gut microflora and intestinal protozoa but also on metabolism. Their variable composition is also thought to be a factor.
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