Objective: Growth Promotion

Antibiotics are one of the crucial medical discoveries of the 20th century and still have significance for treating humans and animals in the 21st century. Risks of antibiotic resistance and antibiotic residues in products of animal origin and in the environment have raised health concerns among the public and scientific community about the risk of so-called ‘superbugs’. The banning of AGPs has had a negative impact on animal performance in some countries. The next generation of growth promoters includes novel, natural strategies tailored to mimic growth promotional effects of AGPs and even have additional benefits, such as the promotion of beneficial gut bacteria, meat and egg quality improvement or reduced environmental emissions.

Aiming for performance

Plant-derived substances have been used for centuries for the purposes of flavoring as well for their beneficial effect on the organism (biological effect). Digestarom®, a selected and standardized blend of herbs, spices, essential oils and extracts, has shown to be able to achieve comparable results in animal production as with applying selected AGPs.

Scientific findings demonstrate that a phytogenic feed additive (PFA) such as Digestarom® can improve broiler performance, delivering similar or better results compared to AGPs. In one study, broilers receiving a Digestarom® supplemented diet recorded higher body weight gain and improved feed conversion compared to both the control and AGP groups (Figure 1).

Figure 1. Phytogenic feed additive delivers best broiler performance in trial up to 39 days of age.

Three keys to growth promotion

The formulation of Digestarom®, a phytogenic feed additive, contains three major modules that target: (1) appetizing and digestive secretion enhancement, (2) gut microbiota modulation and (3) gut protection. For the first module, digestive secretion enhancing effects support nitrogen retention and improved digestibility that contribute to better feed efficiency. The second module shifts the intestinal microbiota balance towards more favorable bacteria. The third module decreases the inflammatory response in animals, preserving that otherwise spent energy for growth, and increases the anti-oxidant status of gastrointestinal cells. Combined, these modules deliver not just performance enhancement, but also additional benefits, such as the promotion of beneficial gut bacteria, meat and egg quality improvement or reduced environmental emissions.

The mode of action of AGPs has been discussed considerably in literature. Aside from the antimicrobial effect, several hypotheses were proposed to explain the resulting growth enhancement. Explanations included an interference with the microbial toxin production or increased nutrient absorption due to changes in the intestine. Studies have also shown that some but not all AGPs are involved in the inhibition of the inflammatory response.

Given that feed additives and antibiotic growth promoters only partly rely upon identical modes of action, it comes as no surprise that their effects can also vary. Selecting the appropriate management goal tailored to specific farm conditions can help to achieve the desired outcome. Farm management plays a crucial role in the achievement of positive results.

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Phytogenics counteract gram-positive bacteria

Phenolic compoundsPhenolic compounds (a group which includes e.g. thymol and carvacrol; major active compound in thyme and oregano) within essential oils and other essential oil derivatives have all been shown to have antimicrobial properties, though these tend to target gram-positive bacteria. Gram-negative bacteria, however, possess an outer cell membrane that limit the antimicrobial effect of phytogenic constituents. A permeabilizing substance that weakens this outer membrane can allow antimicrobial agents, including phytochemical and a blend of organic acids, to act effectively to reduce the Gram-negative bacterial load.

Figure 2 illustrates the effectiveness of the Biotronic® Top product line, which combines selected organic acids and their salts with a phytochemical and the unique Biomin® Permeabilizing Complex, in combatting gram-negative bacteria such as Salmonella enteritidis in broilers. (See also “Is Zero Salmonella Possible?” in Science & Solutions Issue 4). Besides the reduction of the pathogenic bacteria, Biotronic® products are also known to increase the number of beneficial bacteria in the intestinal tract of poultry. Overall, a healthy digestive tract will lead to a better performance of the animals.

Figure 2. S. enteritidis counts in the cecal content of broilers on day 5 and day 10 post infection.

Coccidioisis challenge

Probiotics and phytogenic feed additives, with or without the use of coccidiostats or vaccines, can help alleviate the negative effects of coccidia infection. Both, but particularly probiotics, have shown to be a novel strategy to manage coccidiosis in poultry. The host-specific multispecies synbiotic, PoultryStar®, reduces intestinal lesions, oocyst count in dropping and mortality which are positively reflected on performance (Figure 3). Hence it is able to alleviate the impact of internal parasite infection on chickens by improving gut integrity, reducing sporozoite invasion into the intestinal epithelium and modulating the bird’s immune response.

Figure 3. Weekly oocysts shedding per gram of dropping in Ross 308 broilers. On day 2 all birds received an artificial coccidiosis infection.


The reduction of sub therapeutic antibiotic use is set to continue. Numerous trials and studies indicate the effectiveness of Digestarom® in promoting growth and feed efficiency. In the case of a Gram-negative bacteria challenge and growth promoting effect, Biotronic® has demonstrated effectiveness in both scientific and field trials. PoultryStar® has demonstrated high efficacy in the competitive exclusion of pathogenic bacteria. A more granular framework that allows for the distinction between health and production efficiency— two closely related objectives — can help to guide the application of feed additives that deliver the greatest benefit to birds and producers.