The use of natural growth promoters (NGPs) in feed and water for poultry is increasingly common. The objective is to prevent gut diseases, to enhance performance and also to decrease medication costs.

NGPs are promoted as potential substitutes to antibiotics, which are used for treatment or as growth promoters. They are usually tested against each other, and few strategies suggest their combination during a production cycle.

Since the 1940s, antibiotics have been used in poultry feed as growth promoters (AGPs) or as a treatment against diseases through feed and water. An AGP is included in feed to improve performance and to control sub-clinical gut infections, whereas an antibiotic treatment addresses an identified disease.

Antibiotics are chemotherapeutic agents which kill or inhibit gram positive and/or gram negative bacteria. These substances can have a particular target or be broad-spectrum.

The use of antibiotics, their residues in food and have become topics of tremendous interest. While antibiotics were a great discovery for animal production in the 1940s and 1950s, in the late 1990s, in Europe, pressure to remove AGPs was gradually increasing. AGPs have even been banned in feed by the European Union since 2006 and also by an important fast-food chain in US. In animal production, and particularly in poultry production, the misuse and the overuse of antibiotics has been associated with the emergence of bacterial resistance.

The restrictions on AGPs, when implemented, resulted in a negative impact on live broiler performance. Litter conditions and the control of enteric disease became more difficult to manage.

Feed quality and farm management improved in an attempt to keep birds in good health and to maintain high performance, and NGPs became a realistic option to substitute, at least partially, the ban, or the decrease, of antibiotic use.

Many solutions are available as NGPs, including probiotics, essential oils, plant extracts, organic acids, prebiotics and enzymes. Both antibiotics and NGPs have the capacity to balance the gut bacterial flora, to reduce the nutrients available for pathogens, to improve growth performance and feed efficiency, to improve food safety, and finally to enhance animal welfare by decreasing various stresses. Nevertheless, their mode of action can be very different.

Probiotics and antibiotics

Probiotics are products containing single or mixed strains of bacteria that can establish a balanced gut flora in terms of quantity and quality, but also, in some cases, diversity.

Probiotics are able to exclude the colonization of pathogens in the gut of poultry, and establish a beneficial flora, producing antimicrobial substances and stimulating the immune system. Administration is recommended during the first days of life and around digestive stresses, such as feed changes, vaccination or antibiotic treatment. Performance can be improved considering these modes of action. By applying a multi-strain probiotic in drinking water at 3 periods in the production cycle of broilers (1-3 days of age, 10-12 days, 18-20 days), for example, has shown an improvement of 94g of weight gain at 40 days and an improvement of 0.04 for the feed conversion (FCR).

In this case, the probiotic would be applied during the first days of life through water application. By definition, an antibiotic treatment should not be applied at the same time via water.

The presence of an AGP in feed at the same time, is not necessarily contradictory. In fact it can be possible that the level of antibiotic in the feed is low and that the quantity of probiotic (cfu/g product) provided is sufficiently high.

As a complementary combination, the right and most effective probiotics can also be used through water to fight Clostridium perfringens and necrotic enteritis in the gut. Another option is to apply probiotics after an antibiotic treatment. Indeed, a probiotic will re-establish a beneficial gut microflora after the bactericidal action of the antibiotic.

Essential oils and antibiotics

Essential oils (EOs) originate from extracts of herbs and spices. They can be natural or synthetic and contain one or several active molecules. Carvacrol, thymol, eugenol, cinnamaldehyde are some examples and they are known to have antimicrobial, antioxidative and flavouring properties. Moreover, it has been speculated that EOs stimulate digestive enzyme secretions.

Applegate et al. (2009) have shown that a blend of different oils and a prebiotic has enhanced the performance and health status of birds infected with coccidian (subclinical condistions). Mac Reynold et al., (2008) also showed that the same mixture was able to decrease the severity of a necrotic enteritis challenge. Sub-clinical coccidiosis and necrotic enteritis are two common problems on many poultry farms and both problems are also very linked. The use of this blend in complement to antibiotics (AGP or treatment) against necrotic enteritis can provide a complementary effect.

A supplementary effect that EOs give to antibiotics is their activity on the digestive enzyme secretion and their ability to improve the absorption surface of the gut and the feed digestibility.

Organic acids and antibiotics

Organic acids are a relevant tool to manage feed and water hygiene. In addition to these two main functions, organic acids can reduce the pH of the digestive tract, can lower the bacterial count in the gut and act against gram negative bacteria. It has been concluded that organic acids added to water could at least reduce the transmission of campylobacter in a flock. To limit the proliferation of bacteria in the water, lowering its pH is also essential to control.

Through their ability to improve hygiene, organic acids are a good solution to support the bactericidal effect of AGPs in the gut. Moreover, their strong action on gram negative bacteria acts as a complementary solution to antibiotics such as bacitracin and tylosin, which have a primarily gram positive spectrum. While treating a specific disease, it is also logical that water and feed hygiene should still be strictly controlled. Nevertheless, the water applicable antibiotics have an optimum pH for a good efficiency, therefore the organic acid application should be driven considering this.

Despite the fact that NGPs are mainly positioned as substitutes to antibiotics, it is worth considering the potential combination of NGPs and antibiotics, as growth promoters, and for prevention or treatment.
By applying a well though-out strategy, the complementary and supplementary effects of NGPs can be added to the effect of antibiotics. Antibiotic overuse could be avoided and some treatments could be saved by applying this strategy.