Beyond AGPs : seeking new broiler growth promoters-one company’s experience

The increase in demand for cheap food and advent of modern production methods in agriculture have given rise to the use of synthetic compounds in feed, for example, sub-therapeutic antibiotic supplementation. For the past half-century, low, prophylactic doses of antibiotics have been standard practice. Although the response to antibiotic growth promoters (AGP) depends on a number of factors, including farm management, exposure to pathogens, environmental stresses and diet, their use is well recognised to improve the rate and uniformity of broiler growth whilst increasing feed efficiency.

The biggest concern regarding the continued used of antibiotics in animal feed is the development of direct antibiotic resistance of pathogens in the species receiving the feed, as well as the indirect resistance to similar antibiotics used in human medicine as the result of food chain residues. Public concern and government regulations increasingly press for restricting the use of antibiotics as AGP.

The European Union (EU) began to suspend licences for several major antibiotics in 1971. This process has come to an end and since 1st January 2006, licences for all sub-therapeutic levels for growth promotion have been withdrawn. Producers in several countries that export poultrymeat to the EU have to follow the EU guidelines. There is also a demand for alternatives to AGP in an increasingly health-conscious market. Some producers have imposed a 'commercial' ban on use of AGP in order to market meat and eggs guaranteed free of AGP. Ahead of the EU ban on AGP in 2006, In Vivo NSA, formally Evialis, as one of the leaders in the European feed market, began work on the best way to replace AGP.

Role of gut microflora?

The gastrointestinal microflora of chickens play a significant role in nutrition and growth. The competition offered by gut microflora for nutrients in poultry can be managed in part through the use of low levels of antibiotics. This option is rapidly disappearing. As a result, there is a need to understand the role played by microflora in order to manage the effects on nutrition, growth, health and disease by suitable replacements for antibiotics.

In chickens, the gut microflora play a minor role in digestion of feed ingredients but an important role in absorption of nutrients.

Gut microbes may be beneficial or harmful. Beneficial bacteria inhibit the growth of pathogenic bacteria and prevent some specific intestinal diseases such as Clostridium perfringens and E. coli. Any disruption in this balance may cause the proliferation of pathogenic or performance- hindering microflora.

What can we expect without AGP?

The ban on in-feed antibiotics has left the industry at higher from increased mortality and performance variability.

Clostridium perfringens is associated with necrotic enteritis (NE) and a general over-growth of pathogenic microflora in the intestine may lead to enteric disorders and wet litter.

Good litter quality has always be a difficult area to control for the widely used practice of rearing broilers on the floor. Wet litter is associated with the following major effects:

Loss of weight gain and performance
Increased respiratory and leg problems
Increased downgrading at processing.
Increased use of therapeutic antibiotics

The degree and severity of enteric disorders depend on chick quality and management such as brooding conditions but diet formulation is also a key factor:

Levels of minerals (potassium, chloride, sodium)
Excessive level or unbalanced protein
Fat source - different digestibility coefficients
Starch source - digested at different rates, which impacts the composition of the microflora.
Non-starch polysaccharides - these poorly digested fibre components found in wheat, barley and rye make birds susceptible to enteric disease.
Particle size - coarser particles increase gizzard function, which improves digestibility and intestinal integrity.

As these feed factors are not easily controlled, there is great interest in developing natural alternative supplements to AGP in order to maintain both animal performance and welfare.

In search of alternative natural solutions

A wide range of alternative products have been proposed to feed manufacturers to replace the AGPs following their complete ban in 2006.

Many, such as the feed enzymes, have been around for several years, and have enjoyed success on some poultry diets. Others, probiotics and plant extracts are already quite popular in human nutrition and therapy, and through dedicated research and development, are also popular candidates for poultry feed. Acidifiers, prebiotics, probiotics and herbal products are already in use in some feeding programmes. They limit number of pathogenic bacteria, enhance the absorptive capacity of the small intestine and improve performance.

The search for the best alternatives made difficult by a lack of knowledge about the mode of action of AGPs. To select suitable candidates on a scientific basis, In Vivo NSA has carried out several trials in its Research Centre of Saint-Nolff. Since 2000, different commercial products have been tested alone and in combination, and at different doses.

Each experiment included a negative control (no AGP) and 10ppm avilamycin. Avilamycin is no longer permitted in EU but it was used as a positive control to gain a better understanding of results.

The results vary widely from one experiment to the other. In half of the experiments, the performance of the positive control was no better than the negative one. Therefore, the results are presented in Table 1, in two groups: group 1 includes trials where the negative control was better than positive control; group 2 includes those where the positive control was better than the negative control.

Table 1: Overall performance of groups 1 and 2 (negative control = 100) at In Vivo NSA research station

	Growth	Feed conversion
	Avilamycin	Alternatives	Avilamycin	Alternatives
Group 1	98.72	101.48	100.30	99.70
Group 2	103.03	99.33	99.45	99.82

These results indicate that in the good conditions of an experimental research farm, the improvements in performance due to AGPs are not important overall, and that the individual results are not constant between flocks. The most important effect seems to be on growth. Similarly, the alternatives - fed alone or in combination - have inconsistent effects on performance.

Surprisingly, it seems that the average effects of the tested alternatives are opposite to avilamycin. Avilamycin is mostly active against gram-positive bacteria, so the observations could relate to differences in the digestive flora of the birds in the different experiments.

These data confirm that the selection of AGP substitutes from experimental results under good sanitary conditions need special consideration, and highlight the importance of a suitable experimental protocol in such trials.

Results in challenging situation

The imposition of various challenges - microbial infections, viscous feed, high stocking density - can be used make the conditions of an experimental station more like those of a commercial farm. There follow details of two trials to test the In Vivo NSA product, a natural synergetic mix of synthetic and natural clays, essential oils and plant extracts.

Figure 1 show results from an experiment in Brazil where the use of AGPs is still permitted. It compares with 8 pens (56 birds/pen) per treatment. There was a negative control without AGP or challenge. This was compared with three treatments that involved a challenge in the form of re-used litter): a negative control, a positive control (10ppm virginiamycin) and the Evialis product.

Figure 1: Example of experimental trial with challenge (In Vivo NSA, Brazil)

Beyond AGPs : seeking new broiler growth promoters-one company’s experience - Image 1

An experiment from the Netherlands compared a negative control without challenge to two treatments using highly viscous feed and microbial challenge: a negative control (without additives) and the In Vivo NSA product. The results are shown in table 2.

Table 2: Example of experimental trial with challenge (North European feed company)

Beyond AGPs : seeking new broiler growth promoters-one company’s experience - Image 2

Both tests show how various challenges impair the performance of broilers, and how some feed additives may allow a recovery in growth and feed conversion following an earlier set-back. Note also that such experimental trials may provide additional information such as litter scoring (table 2), an important parameter for growers. Trials that simulate field conditions can stimulate interest in the use of alternative growth promoters

Interest of organized field trial

Varying conditions of husbandry, age of birds, disease patterns and management support the need for a series of well organized long-term field studies. Not only can they take into account the variations in commercial broiler growing but they may help to establish significant differences between treatments. Table 3 shows the results of a series of trial with a Turkish broiler integrator. Despite repetition of the test at the same time of year and on the same broiler breed, the results showed considerable variation, with some tests showing improved growth and others demonstrating better feed conversion. This variability is typical of field conditions.

Table 3: Results of broiler performance in five field tests (14,000-27,000 birds/house on three broiler farms in Turkey)

	Daily gain (g/d)	FCR	Mortality %
	Evialis product	Control	Evialis product	Control	Evialis product	Control
Average of 5 tests	51.4	49.3	1.85	1.89	3.8	3.5
Test 1 - 46 days (Control = Avilamycin )	46.9	47.6	1.80	1.89	3.9	4.1
Test 2 - 45 days (Control = MOS : Mannan Oligosaccharide)	50.4	51.5	1.91	1.95	1.8	1.9
Test 3 - 44 days (Control = MOS)	55.1	50.2	1.84	1.84	3.3	2.4
Test 4 - 45 days (Control = MOS)	54.3	49.0	1.82	1.86	7.2	4.4
Test 5 - 43 days (Control = MOS)	50.7	48.0	1.88	1.93	2.9	4.5

Evialis - In Vivo NSA experience shows that potential natural growth promoters should be firstly screened at an experimental station under challenging conditions. This should be followed by a series of organized field tests in order to address the variation in situations found in the field and to review the cost-effectiveness of AGP alternatives under commercial conditions.