In the short lifespan of broiler chickens, the later that micro organisms colonise the intestinal tract, the more vulner­able is the birds’ intestinal ecosystem. Conventional solutions to protect the young birds typically involve feeding sub-therapeutic doses of pharmaceutical-type antibiotics. However, there is increasing concern of regulatory bodies and the public opinion around the world about the use of such ‘antibiotic growth promoters’ or AGPs.

Thus the global search for new solutions is intensifying, accelerated by the impending ban of all AGPs in food animal feeds for the European Union in 2006. Direct-fed microbial or probiotic products consisting of natural sources of beneficial micro organisms already are available to help maintain the balance of the intestinal micro flora in a range of food animal species. Now much of the research and development is on poultry, where the challenges can be distinct from other species. However, recent trials under farm conditions suggest that probiotics with consistent efficacy are going to provide a reliable solution for managing the balance of the gastro-intestinal flora in commercial broilers.

Probiotic challenge

In the natural environment, the intestinal tract of chickens is colonised by a broad range of micro organisms at a very early age of the birds. By far the most typical source of the intestinal flora is the unsterile surface of the egg, resulting from contact with the hen in the nest. In commercial operations, however, the colonisation of the intestinal tract is a more prolonged process due to the high hygienic standard in the hatcheries and the lack of contact with the natural environment.

It takes around 21 days for broilers to develop a balanced intestinal flora, and this period represents around 50% of a broiler’s life. Unfortunately, the later the intestinal tract is colonised, the more vulnerable the intestinal ecosystem will be to pathogenic organisms. After the first 21 days, other challenges such as stress, feed changes, antibiotic interventions, and disease can upset the gastro-intestinal tract (GIT) flora and cause considerable losses.

Feed-type probiotic products consisting of beneficial micro can help establish and maintain the balance of the intestinal micro flora in commercial broilers. However, one of the key factors in their efficacy is their stability during storage and feed processing. Heat treatment and pressure during pelleting are the toughest obstacles for beneficial micro organisms to reach the GIT.

The best natural solution to the challenge of stability in direct-fed microbial products is to use spore-forming beneficial strains of microbes. A spore is a livable cell protected by its own natural coating, not encapsulated or otherwise coated in a manufacturing process. Selecting a probiotic micro organism that has beneficial effect in broiler chickens, however, requires a steady search for the best candidate which stands the test under practical conditions. A single, superior strain of spore-forming beneficial bacteria may be preferred due to advantages in manufacturing quality assurance and in simplicity of regulatory registration.

Feeding trials with broilers

A proprietary, thermo-tolerant, probiotic strain of Bacillus subtilis has been tested in feeding trials with broilers in several countries. The results obtained have shown consistent improvement of feed conversion rate and body weight gain under a wide variety of commercial conditions. The beneficial results obtained from this probiotic strain have appeared to occur due to an effect over the GIT microbiota balance, improving the intestinal health and integrity, that has translated into a better general health and consequently enhanced performance.

Trials in Brazil and the USA have provided significant evi­dence that broiler production can be improved by using a single strain of B. subtilis throughout the production period.

The broiler pen trials reported here followed an experimental model which included a negative (unsupplemented) control, positive (antibiotic) control, and the B. subtilis probiotic (Table).

Table

Broiler chicken performance in recent 42-day pen trials comparing diets of negative control, antibiotic control, and a proprietary probiotic strain of Bacillus subtilis

These three litter pen trials in Brazil and the USA were conducted under commercial-type conditions using standard diets, commercial broiler strains, and typical industry management practices such as built-up litter top-dressed with fresh wood shavings. The objective of these trials was to demonstrate growth responses and feed conversion in broiler chickens using either the probiotic-supplemented or AGP-supplemented diets compared to negative control diets. Researchers averaged key performance parameters - body weight, feed conversion, and mortality - over the three trials (Figures 1, 2, and 3).

Figures 1.,2.,3.

Summary of broiler chicken trials in Brazil and the USA, comparing a direct-fed, single-strain Bacillus subtilis probiotic versus conventional antibiotic growth promoter and non-AGP controls

Note: In all trials, proprietary Bacillus subtilis as GalliPro 8x10⁵ from Chr Hansen

Trials in Brazil and USA

A trial was carried out at Viçosa Federal University using Ross male broiler chicks at stocking density of 9.52 birds per square metre on used litter (one previous flock). Salinomycin was added to the mash feeds as a coccidiostat. There were 10 replicate pens of 22 chicks each per treatment. The experi­ment was conducted during the winter. Birds treated with the proprietary B. subtilis strain showed no significant difference when compared to avilamycin for increasing 42-day body weight or improving feed conversion, and both treatments were significantly better (P<0.001) in body weight than the negative control.

Another trial at Virginia Diversified Research Corp, Harrisonburg, Virginia, placed 60 Cobb straight-run chicks per pen (10 replicate pens/treatment) at 16.12 birds per square metre on used litter with acovering of fresh wood shavings in a spring season trial. Monensin at 99 ppm was added to the mash feeds as a coccidiostat. The stocking density and used litter were applied to simulate what is found in commercial conditions. The broiler chickens treated with either the B. subtilis product or the AGP significantly (P<0.05) improved 42-day body weight and feed conversion ratio compared to the negative control. The diets with bacitracin-MD at 55 ppm significantly (P<0.05) lowered overall mortality compared to negative control diets.

A summer pen trial was carried out at Southern Poultry Research, Inc, in Athens, Georgia, using pelleted feeds con­taining monensin at 100 ppm as a coccidiostat. Cobb male chicks were placed 50 per pen in 36 replicate pens (9 pens per treatment) at a stocking density of 11.62 birds per square metre. Each pen had about 10 cm of built-up litter top-dressed with fresh pine shavings. Compared to the negative control results, significant improvements in 42-day body weight (P<0.056) and feed conversion ratio (P<0.001) were observed for the B. subtilis treatment, and feed conversion ratio was better for the virginiamycin-fed birds than for negative controls.

These trials in Brazil and the USA showed that inclusion of the proprietary strain of Bacillus subtilis in broiler chicken diets at a level of 8x1O⁵ colony forming units per gram of feed was effective at improving body weight and feed conversion ratio at market age compared to negative control diets. The trials showed that the probiotic product did not differ significantly from the respective antibiotics used as growth promoters for improving feed conversion ratio in all trials. The probiotic product also increased body weight of birds at the AGP level in two of three trials. This research has suggested that a new spores-forming probiotic strain may be recommended for use under commercial-type growing conditions. Thus the single-strain probiotic or direct-fed microbial approach has shown potential as an economical replacement for AGPs to improve live performance of broiler chickens.

Employed by international feed and food ingredients supplier Chr Hansen, Dr Carvalho is based in Brazil and Mr Hansen is based in Denmark. Please contact Dr Carvalho at nelson.carvalho@br.chr-hansen.com Complete references for this article are available directly from the lead author Dr Carvalho.

Feed International,Vol.26,#10,november/december 2005.,Watt Publishing Co., USA

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