IAN PARTRIDGE
New Business Development,
Animal Nutrition and Health,
DSM Nutritional Products Asia Pacific Pte Ltd, Singapore
Throughout Asia regulatory bodies are increasingly considering restricting the use of prophylactic antibiotic use in animal production. Even without regulatory restrictions the use of antibiotic alternatives in Asia is increasing because of growing opportunities for export to European markets and mounting consumer pressure as awareness of environmental and “green” issues increases. The following paper provides a review of products currently available, and being used in Europe, as alternatives to antibiotic feed additives.
Introduction
Pathogenic bacteria are always present in the gut, but the balance between pathogenic and beneficial bacteria determines whether or not disease will occur (Ivanov, 2003). Maintaining a healthy balance between all microflora within the gut is known as eubiosis (Jensen, 1980) and can be influenced by bacteria endemic to the microflora.
In the intestine, bacteria considered beneficial to the gut, including lactic acid forming bacteria like Lactobacillus spp, prevent proliferation of pathogens, such as Salmonella spp., through competitive exclusion for nutrients and for receptor sites on the gut wall (Thomke and Elwinger, 1998). Beneficial bacteria can also produce an adverse environment for pathogenic bacteria to colonise and grow, for example, by the production of short-chain fatty acids which lower the pH and prevent growth of pH sensitive pathogenic bacteria (Thomke and Elwinger, 1998). The intestine is the biggest immune organ in the body, but to achieve appropriate protection from pathogens a complex gut microflora is essential.
The microflora also have functions in the development of the digestive and immune tissue in the host animal, can produce nutrients that can be used by the host as a nutrient source and also can neutralize some feed toxins and promote an environment in the gut where anti-nutritional factors and toxins are minimised ( Dawson, 2001).
In the past, manipulation of the microflora to create eubiosis has been achieved by the use of antibiotic feed additives. However, with the severe restriction of antibiotic feed additive use in the EU and increasing consumer concern in markets such as Japan, alternatives to antibiotic feed additives have been investigated and found to significantly influence this balance also.
Eubiotics defined
a) Probiotics
The generally accepted definition of probiotics comes from Fuller and states that probiotics are microorganisms that have a positive effect on the host by improving the balance of pathogenic to beneficial bacteria in the gut (Simon, Jadamus and Vahjen, 2001). The benefits of probiotics are based on two main functions, stimulating the growth of beneficial microflora and suppressing the growth of pathogenic bacteria (Wenk, 2003). The potential health benefits associated with using a probiotic include improved digestion, stimulation of gastrointestinal immunity and increased natural resistance to enteric disease (Turner, Dritz and Minton, 2001). Although it is known that probiotics do produce these benefits to health a general mechanism of action for probiotics remains unclear, possibly due to the fact that different probiotics (i.e. different types of bacteria) have different modes of action (Turner et al., 2001).
Modes of action that have been suggested include increasing the number of beneficial bacteria in the intestine and therefore improving the ratio of beneficial bacteria to pathogens (Simon et al., 2001). When a higher number of beneficial bacteria are present they are more likely to out-compete the pathogens for both nutrients and adhesion sites on the gut wall, a process known as competitive exclusion. Beneficial bacteria, such as Lactobacillus, are also known to release short chain fatty acids, bacteriocins and hydrogen peroxide, which have antagonistic effects on pathogenic bacteria (Thomke and Elwinger, 1998; Klein-Hessling, 2001).
An example of the effect of a probiotic on broiler performance is shown on Table 1. Trial A shows a positive effect of a live probiotic product containing Enterococcus faecium against a negative control, containing no antibiotic treatment. Both weight gain and feed conversion ratio were significantly improved by administration of the probiotic. Trial B indicates that when the same probiotic was tested against a diet containing antibiotics there was no significant differences in performance. These results demonstrate that probiotics can act as a viable alternative to antibiotic feed additives.
b) Direct Acting Gut Flora Modulators
Direct acting gut flora modulators are defined as compounds directly modulating the microflora via growth inhibition and include products such as organic acids and plant extracts.
Organic acids. Organic acids are now routinely used in weaning piglets during the transition from suckling milk to consuming solid feed to aid in acidifying the feed to prevent bacterial growth and improve digestion of feed ingredients (Miller, 2006). The results of a trail investigating the effect of one type of organic acid on performance in weaning piglets are summarized in Table 2. These results showed that addition of Benzoic acid increased growth rate, feed intake and feed utilization efficiency in weaning piglets.
Use of organic acids is not generally practiced in poultry as the results tend not to be as reproducible or significant as those found in swine (Alcicek, Bozkurt and Cabuk, 2004; Miller, 2006).
Plant extracts. There are many different types of plant extract products available commercially and the definitions vary accordingly. Essential oils (EO) tend to be the oils extracted from plants, but these vary depending on plant species, soil type, climatic conditions, harvesting conditions and storage (Baidoo and Ariza-Nieto, 2005). Essential oil compounds (EOC) refer to the specific active compounds from essential oils (Baidoo and Ariza-Nieto, 2005). Whereas a mixture of essential oils may vary in the active ingredients due to natural variation in the plants from which they were derived, a mixture of essential oil compounds will be consistent, reproducible and measurable.
The modes of action for EO and EOC can vary widely depending on the concentration of the active compound. The principal uses of EOC mixtures in poultry feeding are in regulating gut microflora, specifically limiting the growth of Clostridia perfringens, and stimulating digestive enzymes (Baidoo and Ariza-Nieto, 2005). By achieving this EOC mixtures can be used as an alternative to antibiotic growth promoters and result in enhanced performance.
The results of a broiler growth study comparing the effect of an EOC feed additive (CRINA Poultry) with an antibiotic feed additive (Colistin), are summarized in Table 3. There were no significant differences in performance measures between the positive control and the EOC treatment groups, suggesting that CRINA Poultry was as effective in promoting growth as the antibiotic feed additive.
c) Prebiotics
Prebiotics are defined as a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or the activity of certain bacteria in the colon resulting in an improvement in host health (Wenk, 2003). Prebiotics are oligosaccharides that are not digestible by the animal, but can be fermented in the intestine and act as a nutrient source for lactic acid-producing bacteria such as specific strains of bifidobacteria (Wenk, 2003).
Conclusions
Digestion and immunity are critically dependent on gut microflora. Whilst pathogenic bacteria are always present in the gut, the balance of non-pathogenic and pathogenic bacteria will strongly influence the disease status of the bird. Modulation of these two types of bacteria within the gut to produce a healthy balance of microflora, or eubiosis, can be achieved by a variety of products, including probiotics, direct acting gut flora modulators and prebiotics.
The search for effective alternatives to antibiotic feed additives has intensified as a result of the ban on antibiotic growth promoters in Europe. Earlier research with these products showed some to have limited efficacy. Now, however, with advancing research and development in this field, some newer products have been shown to give results that are as effective as antibiotic growth promoters in maintaining health status and enhancing monogastric growth performance.
References
Alcicek, A., Bozkurt, M. and Cabuk, M. (2004). South African Journal of Animal Science. 34(4): 217-222.
Baidoo, S. K. and Ariza-Nieto, C. (2005). 2005 Allen D. Leman Swine Conference. 213-222.
Dawson, K. A. (2001). Proceedings of the 2nd International Poultry Broiler Nutritionists’
Conference, 2001: 74-87. Ivanov, I. E. (2003). Poultry International, June: 33-37. Jensen, B. (1980). Tissue cleansing through bowel management. Bernard Jensen International, New York.
Klein-Hessling, H. (2001). 62nd Minnesota Nutrition Conference, 2001.
Miller, H. M. (2006). World Nutrition Forum – 2006. 95 – 101. Simon, O., Jadamus, A. and Vahjen, W. (2001). Journal of Animal and Feed Sciences. 10, Suppl. 1: 51-67.
Thomke, S. and Elwinger, K. (1998). Ann. Zootech. 47: 245-271. Turner, J. L., Pas, Dritz, S. S. and Minton, J. E. (2001). The Professional Animal Scientist, 7: 217-226.
Wenk, C. (2003). Pig News and Information, 24(1): 11N-16N
From Proceedings of the “19th Australian Poultry Science Symposium”, New South Wales, Australia.
