Sorting through antibiotic alternatives is no easy task
As the search for antibiotic replacements continues, a host of products are being marketed to take their place with clear winners difficult to identify.
Nearly two years after the European Union Legislature removed the last antibiotic growth promoters from pig and poultry diets, the subject of finding alternatives to these additives continues to attract intense interest, both inside and outside Europe. An illustration of this occurred only a few weeks ago. Delegates to an international animal congress in Ireland packed into a special workshop held to present some results from a cross-national research project on developing natural alternatives to the use of growth-promoting antibiotics in feeds.
The workshop, called Feed for Pig Health,' took place during the 2007 congress of the European Association of Animal Production, held in Dublin. It referred to the 4 million multidisciplinary project that has involved institutes in several countries and is backed by European Union funds. The research examined plant extracts and other natural substances as possibilities to reduce the use of antimicrobial feed additives in the weaned pig.
Plant extracts were evaluated initially through an in vitro screening process. From there, a small representative group was categorized for their effect on specific established indicators of gut health. The evaluation also covered prebiotics, fermented liquid feed and organic acids, underscoring the notion that the search for alternatives still has not focused on one particular ingredient type.
During a presentation by Nutreco Group representatives to Asian clients at this year's VIV Asia show in Thailand, there was indication that health-promoting feed products could be placed in four main categories according to their mode of action. Prebiotics and immunoglobulin products, for example, are categorized as inhibiting the attachment of pathogenic microbes to the lining of the gut wall. Organic acids, medium-chain fatty acids, essential oils and herbal extracts are considered as inhibiting the proliferation of these pathogens. Then there are the competitive exclusion products exemplified by probiotics and the immune-system stimulants such as yeast glucan materials and betaine. But as numerous trials have confirmed, response can vary widely even for products within the same category.
And now it's being suggested that too much emphasis has been placed almost entirely on the mechanism of action for replacement products, rather than understanding the volume and duration of their effects.
Questions for suppliers
In 2004, our associated journal Pig International reported that a leading animal nutritionist had developed a series of questions to ask suppliers about their prospective replacement products. The recommended questions are worth repeating here as part of this issue's AGP-alternatives coverage.They had been developed for a presentation in Switzerland by UK-based nutritional consultant Dr Gordon Rosen, of Holo Analysis Services Ltd. He identified examples from the categories of enzymes, micro-organisms, organic acids, oligosaccharides and the botanicals including herbs, spices and essential oils. Other categories include aromatics and antioxidants as well as acidity regulators, preservatives, chelates and chemicals. As Dr Rosen pointed out, even this long list would be incomplete without also mentioning nutrients, such as lysine. To assist feed formulators, he proposed these seven questions to ask the supplier:
How many properly-controlled feeding tests do you have on the efficacy of your product? The results of all available controlled tests should be considered. A first appraisal could be based on a minimum of 20 such tests, but a full evaluation would need a minimum of about 50 (preferably more) test results in order to analyze key variables.
How many of these tests have no negative controls? The purpose of a negative control is to determine whether either product is effective by comparison, Dr Rosen comments. Having only a positive control seriously limits the value of the test.
Can you supply a bibliography in answering the first two questions? Publications in a refereed scientific or trade-press journal mean that the full details of tests can be accessed .
How many times out of 10 does your product improve liveweight gain and feed conversion? Response improvement frequencies in the 70 to 75 percent range indicate the product is comparable with antibiotics.
What are the coefficients of variation in the gain and conversion responses? These coefficient of variation ratings will show the difference between a product giving extremely variable responses and one that is as reliable as antibiotics (100 to 200 percent).
What dosage of your product will maximize the return on my investment? This is a key question because economically optimal dosages are not always defined.
Can you supply a model to predict responses to your product under my specific conditions? Dr Rosen remarked that the shortage of suitable prediction models for replacements was in sharp contrast to the wide array of models for the displaced antibiotics.