ReviewAn update on alternatives to antimicrobial growth promoters for broilers
Introduction
Antibiotics have been widely used in animal production for decades. Although some are used therapeutically to improve the health and well-being of animals, most were given for prophylactic purposes and to improve growth rate and feed conversion efficiency (as antimicrobial growth performance promoters, or AGPs). However, due to the emergence of microbes resistant to antibiotics which are used to treat human and animal infections, the European Commission (EC) decided to phase out, and ultimately ban (January 1st 2006), the marketing and use of antibiotics as growth promoters in feed (EC Regulation No. 1831/20031). This political decision was taken by invoking the precautionary principle: ‘Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation’ (Principle 15 of the Rio Declaration, 19922).
In other countries, such as the USA, consumer pressure is pushing the poultry industry to rear animals without AGPs (Dibner and Richards, 2005, Castanon, 2007). AGP removal has led to animal performance problems, feed conversion increases, and a rise in the incidence of certain animal diseases, such as (subclinical) necrotic enteritis (Wierup, 2001, Dibner and Richards, 2005). One disease syndrome that is clearly emerging in the EU broiler industry simultaneously with the ban of growth promoting antibiotics is often referred to as ‘dysbacteriosis’. This is a poorly described condition of the gut and may be synonymous with conditions such as ‘wet litter’, ‘small intestinal bacterial overgrowth’, ‘malabsorption’, and ‘feed passage syndrome’. The common clinical denominator is thinning and ballooning of the small intestine, increased water content of faeces and reduced digestibility of feed with indigested residues visible in the faeces.
The impact of phasing out animal growth promoters could be minimised provided that adequate attention is given to the implementation of alternative disease-prevention strategies and management factors, such as alternative husbandry practices in food animal production. Indeed, overall disease and performance problems have been rather limited, partly because ionophore anticoccidials are still available, therapeutic antibiotic use (e.g. macrolides and penicillins) has increased, and alternatives for AGPs have been empirically used such that those with the best effects on performance are currently used as feed additives.
Section snippets
Characteristics of good AGP alternatives
Ideally, alternatives to growth promoters should have the same beneficial effect as AGPs. It is however not totally clear how AGPs exert their beneficial action. The most well-known mechanism to be proposed is that AGPs have an antibacterial action that favours performance in different ways: (1) by reducing the incidence and severity of subclinical infections (George et al., 1982, Brennan et al., 2003); (2) by reducing the microbial use of nutrients (Snyder and Wostmann, 1987); (3) by improving
Exogenous enzymes
Non-starch polysaccharides (NSPs) in animal feedstuffs are a complex group of components differing widely in chemical composition, physical properties and physiological activity, many of which have negative effects on growth and performance. NSPs include (hemi)celluloses, pectins and oligosaccharides as well as arabinoxylans and β-glucans (consisting of either a more soluble or a non-soluble fraction).
Different cereal types contain variable NSP levels with concomitant differences in chemical
Regulations concerning feed additives for animal use
A zootechnical additive is any additive other than feed material and pre-mixtures used to affect favourably the performance of animals in good health or used to affect favourably the environment. The category ‘zootechnical additive’ can be further divided into four functional groups: (1) digestibility enhancers; these are substances which, when fed to animals, increase the digestibility of the diet, through action on target feed materials; (2) gut flora stabilisers; these are micro-organisms or
Economical considerations
The general health status determining the performance of broilers is multifactorial. Good management relies on continuous monitoring of the flock for health status and performance. Monitoring of the health status requires regular necropsies with determinations of lesion scores, and identification of pathogens including the make-up of an antibiogram. Monitoring of performance requires information such as feed intake and weight gain, flock uniformity, litter score, climatic and other conditions.
Conclusions
Alternatives for AGPs are only of practical significance when they improve animal performance at levels comparable to AGPs. Microbiota modulating and immunomodulatory compounds have potential and are used as feedstuff of feed additives. Enzymes, acids, pre- and probiotics and herbs or etheric oils are some examples of product classes which are used as alternatives for AGPs. Within each product class, numerous products are on the market, and while some products clearly have potential, for others
Conflict of interest statement
None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper.
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