Paul Toplis

After graduating Paul joined RHM Agriculture as assistant nutritionist working on ruminant, pigs and poultry nutrition, becoming National Pig Nutritionist in 1976 and Chief Nutritionist 4 year later. Since 1983 he has traveled widely advising on pig nutrition. Paul was part of the team which led SCA Nutrition to be the first ever livestock feed company to win the Queen’s Award for Export Achievement.
       In 1996, with 3 fellow directors, Paul formed Primary Diets Ltd which has become one of the market leaders in specialist piglet diet manufacture, trading throughout the UK and Europe. He has spoken at conferences and scientific meetings in the USA, Canada, Denmark, Spain, Italy, Greece, Cyprus, South Africa, Australia and New Zealand, and at many farmers’ meetings in the UK.
       Paul is also involved in training stockpeople and advisory visits to pig units. Paul has served for over 20 years on the Agricultural Industries Federation (formerly UKASTA) Legal Affairs & Scientific Committee.

Products with Bacteriostatic Properties

Use of various organic acids in pig diets has been reviewed by Partenen and Mroz (1999). Organic acids have long been used as preservatives because of their ability to prevent spoilage by microbial growth.

What makes organic acids so good as preservatives is their ability to enter a bacterial cell. Once inside the alkaline environment of the bacterial cell’s cytoplasm, the organic acid separates (disassociates), releasing it’s acid anion (H+) component, which acidifies the cell contents. As the H+ anion accumulates within the cell, it inhibits microbial enzymes and the distressed cell attempts to return to equilibrium by pumping out the H+ anion. The energy required to eject the H+ anion is thought to weaken the already distressed cell, slowing growth and reproduction. A further benefit then accrues from the increasing amount of H+ anion pumped back out into the intestinal contents as their acidifying effect favours the acid producing bacteria (lactobacilli, bifidobacteria) and inhibits the acid hating bacteria (Salmonella, E Coli, Campylobacter sp). Dietary acidification brings other benefits; improving gastric proteolysis and protein digestibility, the acid anion can also complex with minerals and increase their digestibility.

Organic acids also serve as substrates in intermediary metabolism and therefore have an energy content (Propionic acid has 1.5 times more energy than wheat).

The dual mode of action of organic acids makes them so attractive, at low pH, they do not disassociate, which allows them to enter and disrupt the bacterial cell. At higher pH, the acid disassociates and inhibits alkaline loving bacteria and favours acid loving ones. By combining several organic acids, which disassociate at different pH levels, it is possible to exploit the effects of both modes of action over a larger proportion of the range of pH found in the pigs intestines.

Essential oils are highly concentrated extracts produced by further refinement of plant extracts (botanicals) by hydro-distillation. Essential oils are used to flavour pig diets to increase their attractiveness to pigs and stockmen. Essential oils are also claimed to have antimicrobial, antioxidant, coccidiostatic and even antiviral properties. (Wenk, C, 2003). Claims are also made for increased digestive enzyme secretion and improved immune function.

Essential oils are standardised products, often based on a blend of plant metabolites such as allylisothiocyanates, thymol, carvacrol, cinnamaldehyde, capsaicin, piperin and others.

In-vitro studies had shown essential oils to have powerful antimicrobial effects. When included in pig diets to flavour them, in accordance with their authorisation, some trials have recorded improved performance over and above the expected improvement from increased appetite alone. (Janroz, D, et al, 2003).

There are reports of synergy between organic acids and essential oils. The synergy is thought to come from the ability of the essential oils to weaken bacterial cell walls, increasing its permeability to the organic acids.

Prebiotics are short chain carbohydrates which cannot be digested or absorbed by the pig and are therefore available for intestinal microflora. Ileal digestibility of Inulin, (a prebiotic), is only 7.5%, but none can be found in faeces, indicating total fermentation in the hind gut. The end products of fermentation are Short Chain Fatty Acids.

Probiotics are live cultures of acid secreting beneficial bacteria.

Both are thought to act by manipulating the indigenous microflora in the intestine to reduce the risk of proliferation of potential pathogens. Through a variety of mechanisms, they are thought to increase resistance to infection.

Various modes of action have been proposed:-

1. Enhancement of the physical barrier (modulation of paracellular permeability, mucosal trophic action).
2. Improved functional barrier (mucosal immunity).
3. Competitive adhesion to epithelial receptors.
4. Reduction of intestinal pH.
5. Modification of bile salts.
6. Competitive exclusion (colonisation resistance).

The first line of defence is to prevent harmful bacteria from entering the intestines by the oral route. Acidic conditions in the stomach are achieved by the secretion of hydrochloric acid to form a powerful antimicrobial barrier. In newly weaned piglets, this mechanism can be inadequately developed and suspect. Lactic acid originating from the fermentation of lactose by lactic acid bacteria (naturally occurring and Probiotic additives) is helpful but limited by the relatively small amount of bacterial activity in the stomach and proximal small intestine. Anything that increases acid production post weaning (Prebiotic SCFA, Probiotic Lactic Acid) can enhance antimicrobial competence and improve the barrier to orally acquired pathogens.

If a healthy gut is defined as an environment with lower populations of E Coli, Salmonella, Staphylococci, Listeria, Shigella, Veillonella, Brachyspiro (Serpulina) and Clostridia, but higher populations of Lactobacilli, Bifidobacteria and Eubacteria, then any substance found to promote that type of intestinal microflora will be valued. Some prebiotics are selectively fermented by Lactobacilli, Bifidobacteria and Eubacteria, whilst being poorly utilised by the potentially harmful bacteria listed above.

It is generally accepted that high villi/crypt depth ratios are indicators of a healthier and more efficient intestinal mucosa. If Prebiotics have a beneficial effect on the gut integrity, it would be expected to show itself in the distal small intestine, at what is thought to be the area with the greatest levels of fermentation. In a recent experiment, ratios were enhanced in proximal and distal sections, but only achieved statistical significance in the distal area. Fermentation was enhanced along the entire small intestine. (Decuypere, J, 2003).

The main end products of bacterial carbohydrate metabolism are acids, short chain fatty acids (SCFA), mainly acetic, propionic and butyric. SCFA are weak organic acids with bacteriostatic properties in common with the organic acids used as preservatives mentioned earlier. SCFA play an important supporting role in the prevention of potentially harmful bacteria escaping the stomach and migrating forward through the small intestine, but more importantly, the reverse flux of harmful bacteria from hind gut to small intestine.

Prebiotics cause increased SCFA production along the gastro-intestinal tract by inducing a shift to a more saccharolytic (carbohydrate fermenting) flora. The presence of fermentable carbohydrates in the pigs diet will reduce protein fermentation, reducing toxic substances such as ammonia, amines, skatol and indole. It is known that increased butyrate concentrations contribute to a healthier intestine because butyric acid is a strong stimulator of the gastrointestinal cell growth, not only for the colonocytes, but also for the enterocytes of the small intestine. (D Pouillard, 2003). Immune cells form part of the intestinal epithelial lining who’s function is to monitor, react and coordinate a response to the components of the intestinal microflora. Pre and probiotics increase the chances of a favourable response to the monitoring process, minimising immune activation with its highly beneficial impact on appetite and nutrient partitioning to growth. Growth responses to Pre and Probiotics achieve statistical significance in the first 14 days after weaning which confirms they can be fast acting in their influences. (Corrent, S, 2002).

A review by Bedford and Schulze (1998) is a useful place to start for anyone wishing further information on enzymes. Addition of enzymes to a pigs diet may supplement the process of digestion which has the double benefit of increasing nutrient availability to the pig whilst reducing the availability of nutrients to the intestinal microflora.

There are immunologically active compounds which may beneficially effect the immune system of the pig. They include mainly antibodies from products such as blood derivatives (eg, plasma protein), freeze dried eggs containing pig related antibodies and possibly some whey protein products. Reduced immune activity promotes growth by increasing appetite and partitioning nutrients to growth.

There is not time to review the considerable list of other products shown to have some antimicrobial activity. Failure to mention them in this paper should not be taken as a negative inference.

This bacteriostatic approach is supported by alteration to the diet to reduce the amount of substrate available to the intestinal microflora. Diets must be modified to reduce “By-Pass Nutrients”! This is best achieved through increased digestibility of ingredients used or by the addition of enzymes to less digestible ingredients. The aim is to reduce the protein and carbohydrate fraction of the diet which can escape digestion and absorption by the pig and remain available as a food source for microbial fermentation by intestinal microflora. Bacterial fermentation of indigestible protein produces ammonia and biogenic amines which are toxic and increase the risk of diarrhoea. Piglet starter diets are highly digestible and may encourage a shift to protein fermentation in the hind gut by being ‘carbohydrate’ deficient. The addition of fermentable carbohydrates (prebiotics) to pig diets has been shown to reduce protein fermentation through increased carbohydrate fermentation in the hind gut. The reduced efficiency of bile salts can be countered by adding emulsifying agents (lecithin) directly to the diet and by improving the saturated to unsaturated fatty acid ratio in the diet to aid absorption. Alterations such as switching from DL-Methionine to Liquid MHA-FA, an organic acid, is another small change which can increase the antimicrobial status of a pig diet. The efficiency of the intestinal epithelium structure and function can be upgraded with the use of Betaine

Primary Diets set out in 1998 to produce an ‘all weather’ product through multiple studies. No “eureka” breakthrough. No high science, but thorough science. We used the University of Leeds to apply rigorous scientific methods to build up a database of growth and FCR responses using several commercially available products from each additive category thought to reduce intestinal microflora. We compared several organic acid products, several essential oils, several prebiotics and so on until we had identified what pigs showed to be the superior products when used within our diets. Then we began combining the winners of each category to test for additivity. After six years this pedestrian but methodical approach has produced a product with a high probability of success in a wide variety of circumstances.

The most successful combination product, according to JSR pigs at the University of Leeds was then compared with a positive control on four large commercial herds with varying degrees of disease challenge and one large, high health herd, against a negative control. These large scale trials can do little more than increase the confidence and comfort factor, as scientific rigour is not available at farm level (no attempt to balance litter of origin across treatment, no access to negative and positive controls against treatment). The apparent consistency of response at farm level during 2004 led us to introduce the product to JSR units at the beginning of 2005. JSR set us the target of having in place, by the end of 2004, the AGP replacer which we would utilise on commercial units in 2006. The aim was to be selecting JSR genetic stock, from pigs fed on a 2006 AGP replacer, throughout 2005. The JSR male and female lines available to UK pig producers in 2006 will have been selected throughout 2005 on test diets containing a 2006 AGP replacer.

What we now have are rather crude products which will efficiently bridge the gap between AGP’s and a new generation of products being developed with the aid of molecular biology. Until recently the microbial community of the intestine has been studied by cultivating commensal bacterial and opportunistic pathogens. Most anaerobic intestinal bacterial are very difficult to cultivate and remain unidentifiable by conventional techniques. Recently a breakthrough has been made in this area by phylogenetic analysis based on the in vitro amplification of the 16s r RNA gene and other phylogenetic markers by polymerase chain reaction (PCR) techniques. (Awati, A, 2005). These have revealed dramatically higher diversity of the intestinal microflora compared to those described by cultivation. A combination of PCR and fingerprinting techniques such as denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) offer opportunities for a great leap forward in our understanding of intestinal microbial populations and for the first time, rapid methods of assessing the effects of different additives and dietary strategies. (Awati, A, 2005). In addition, laboratory models of the GI tract are now sufficiently sophisiticated to allow them to be used to study AGP replacers.

Gene expression profiling holds tremendous promise for dissecting the regulatory mechanisms of complex biological processes, yet relatively little work is being done with livestock animals despite the fundamental importance of the intestines to production animals. Genomic analysis offers the possibility to identify mechanisms and pathways which allow for a rational design of AGP replacers. It may now be possible to achieve in months what we have achieved in years of pig feeding trials.

The challenge for pig producers is not to understand the mode of action of AGP replacers, but to find suitable, reliable and cost effective management routines and feed additives for a sustainable and successful pig production. Health and hygiene will be key to success without AGP’s. There could not be a better time to agree or review a health plan for each pig unit with the veterinary surgeon. Cleaning and disinfection routines should also be reviewed and upgraded if required. The quality of stockmanship and pig management is also fundamentally important in tackling post weaning growth performance and post weaning diarrhoea. Long before Dr Francois Madec became associated with PMWS, he was well known for his classic work on defeating post weaning diarrhoea through improved management and stockmanship. (Madec, F, 1999). Improved stockmanship is one of the more successful AGP replacers. Everyone should have read and acted on the advise set out in the BPEX/MLC booklet “Managing the Withdrawal of Antibiotic Growth Promoters from Pig Feeds”.

The removal of AGP’s in Denmark has led to a dramatic fall in resistance to Avoparcin/Vanomycin in the intestinal bacterial of Danish livestock, but no effect has yet been recorded in the human population (the main point of the exercise!). Studies by the Danish Institute for Food and Veterinary Research (DFVF) have found that imported meat products contained bacteria up to seven times more resistant to antibiotics than those found in Danish meat products. Nine out of ten Danes infected with multi-resistant bacteria have been shown to have contracted the original infection from imported meat. We may reduce the reservoir of antibiotic resistant genes in EU livestock, but that is unlikely to have any impact on the reservoir in humans, while relatively free trade on meat products exists.

The removal of AGP’s increases the cost of production by 40p per weaner and 60p - £1.80 per slaughter pig. AGP’s are thought to have altered the intestinal bacterial population in a way that yielded benefits from intestine-bacteria interactions, which resulted in improved pig performance. A failure to replace AGP’s will result in an increase in adverse intestine-bacteria interactions. Bacteria are important in the regulation of the intestinal function and immunity. Bacteria have a direct influence of the genetic programming of the intestines through direct association with the intestinal cell surfaces. Bacteria communicate with mucosal epithelial cells and modulate cytokine profiles. The expansion and function of the immune system necessitates exposure to bacterial antigens. Dietary additives, nutritional modifications and improved farm hygiene and management can prevent performance and economic loss when antibiotic growth promoters (AGP’s) are removed at the end of 2005. Antibiotic resistant gene reservoirs will diminish in EU livestock but this is not expected to have any impact on antibiotic resistant gene reservoirs in the EU human population, as a sufficient and increasing proportion consume imported meat products.

A list of references is available from gail.rowley@jsr.co.uk

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