Alternatives to antibiotics abound for preventing post-weaning diarrhea

Monday, February 3, 2014

Feed additives which can help maintain a healthy gastrointestinal tract and substitute for antibiotics are showing promise. But more research is needed to understand the effectiveness of these additives, individually or in combination

by JANICE MURPHY

The time immediately after weaning is stressful for piglets, which are highly susceptible to stomach upset during this period. This susceptibility stems from a number of factors, including an immature digestive system, transition from a liquid to solid diet, different environment, transportation, mixing with non-litter mates, and other factors.

Diarrhea is a major cause of mortality and morbidity, resulting in economic losses estimated to be as high as 50 per cent of the production of weaned pigs. While mortality is an issue in these herds, with up to two per cent losses in weaned pigs, the greatest impact comes from the inability to digest properly and reduction in performance. With the added complication of an immature immune system, the digestive system allows opportunistic enteropathogenic bacteria to move in and take advantage of the situation.

To overcome these obstacles, the swine industry has historically fed weaned pigs complex, highly digestible diets formulated with expensive ingredients and sub-therapeutic levels of antibiotics as growth promoters. In light of the current trend to eliminate the use of antibiotics from swine diets, the quest for alternative nutritional strategies for managing newly weaned pigs is ongoing.

Enter eubiotics, feed additives that are capable of maintaining a healthy balance of the microflora in the gastrointestinal tract. Eubiotics play an important role because they not only act locally, but also have an indirect positive systemic effect.

The gastrointestinal tract is a key place to start. It not only serves as the centre for digesting food and absorbing nutrients, it also performs a vital role in providing a barrier to micro-organisms, maintaining a balanced gut microbiota and optimal immune system. When piglets are raised without antibiotics, it is important to optimize these functions with the help of the feeding program.

Researchers have investigated a number of eubiotics, including spray-dried porcine plasma, acidifiers, high levels of zinc and copper, probiotics, prebiotics, nucleotides and nucleotide-rich products, essential oils, egg yolk antibodies, lysozyme, feed enzymes, and herbs and spices. Although research has shown that some of these additives can have a positive impact on the weaning period, either individually or in combinations, the response varies considerably depending on a myriad of factors. As a result, it is critical that nutritionists come to a better understanding of the optimal conditions whereby these additives can impart maximum benefit.

Zinc oxide. A significant number of research and on-farm studies have proven that pharmacological levels of zinc (up to 3,000 ppm) are effective at improving and/or preventing post-weaning diarrhea.

Although the mechanism is not fully understood, it has been suggested that zinc helps regulate the pig's defense mechanisms, gut barrier function and the intestinal microbial population. The results of these studies prove that zinc oxide fed at pharmacological levels can be a cost-effective strategy for controlling diarrhea. However, there are significant concerns about the impact that such high levels of zinc have on the environment.

Organic acids. During the post-weaning period, piglets often struggle to maintain the proper gastric pH due to the rapid change in diet and their inability to produce sufficient amounts of acid in the stomach. Piglets often have gastric pH values in the neighbourhood of 5.0, compared to a mature pig whose pH ranges between 2.0 and 3.0, causing poor nutrient digestion and proliferation of pathogens.

Probiotics. The addition of organic acids such as citric, fumaric, lactic and formic acids is used in order to maintain low gastric pH and address these issues. Organic acid products on the market are currently formulated with either a single acid or a combination of acids but, regardless of the formulation, research has reported inconsistencies in their effectiveness.

Probiotics, by definition, are "live micro-organisms which, when administered in adequate amounts, confer a health benefit on the host."

The mechanisms used by these additives focus on the gut, either by stimulating healthy microbiota, preventing pathogen colonization, improving digestive capacity or lowering  pH, improving immunity or enhancing gut tissue growth and integrity.

There are three categories of organisms commonly used as probiotics – bacillus, yeast and lactic-acid-producing bacteria such as Lactobacillus, Bifidobacterium and Enterococcus. Research studies examining the use of probiotics have reported positive effects on performance and controlling diarrhea in newly weaned piglets. However, the results have not been consistent or, in some cases, repeatable. These inconsistencies may be the result of different doses, strains of bacteria, or variable sanitation conditions and diet types between individual studies.

Prebiotics. A prebiotic is "a selectively fermented ingredient that allows specific changes, both in the composition and (or) activity of microbiota, that confer benefits upon host well-being and health."

Prebiotic supplementation is specifically targeted at stimulating the proliferation of healthy gut bacteria, such as Bifidobacteria and Lactobacilli. Examples of prebiotics include fructooligosaccharides, transoligosaccharides, inulin, sugar beet pulp and coarsely ground wheat bran. Researchers have reported that these additives are successful in altering the composition of the bacterial population and preventing intestinal colonization with pathogenic E. coli in weaned piglets.

Lysozyme. Lysozyme is a muramidase, an enzyme with antimicrobial properties. By breaking certain linkages in the peptidoglycan component of bacterial cell walls, it causes cell death. Researchers at the University of Arkansas and the U.S. Department of Agriculture in Nebraska deemed granulated lysozyme a suitable alternative to antibiotics in 10-day-old pigs consuming liquid diets. They demonstrated that the addition of lysozyme resulted in improved growth performance and small intestinal morphology, as well as decreased Campylobacter prevalence in the digestive tract.

Feed enzymes. The use of feed enzymes is not new. Enzymes have been used to increase nutrient utilization, allow inclusion of low-quality feed ingredients in non-ruminant diets, and help decrease feed costs for many years. However, it has been recently suggested that the role of feed enzymes may be expanded to include maintenance of gut health and function in young animals. This is based on the hypothesis that carbohydrase enzymes working on non-starch polysaccharides can generate hydrolysis products (e.g. oligosaccharides) within the gut, which may in turn have a prebiotic effect. Recent studies at the University of Manitoba have shown that incubating soybean meal, canola meal, wheat and flaxseed with a multi-enzyme blend was successful in generating hydrolysis products such as pectinase, cellulase, mannanase, xylanase, glucanase, galactanase. These enzymes in turn helped maintain gut barrier function in small intestinal segments of piglets challenged with enterotoxigenic E. coli in an in situ perfusion model.

Antibodies. Products with high levels of antibodies against specific pathogens can be effective at controlling incidences of disease caused by those pathogens. Several research studies have shown that supplementing nursery pig diets with products that contain antibodies against E. coli K88, the pathogen responsible for post-weaning diarrhea in piglets, maintains growth performance and minimizes incidences of diarrhea. It is important to understand that, because antibodies are specific to a pathogen, these products work best when used in situations where the target pathogen has been identified as the causative agent for piglet diarrhea.

Nucleotides and nucleotide-rich products. Nucleotides are low-molecular-weight intracellular compounds that are found naturally in all living cells. They are involved in every intracellular function – structural, metabolic, energetic and regulatory – and are present at greater levels in sow milk than in a high-quality creep feed. It has been suggested that, during periods of stress such as weaning, the need for nucleotides may exceed what is supplied endogenously. Researchers have suggested that feeding a diet with added nucleotides might help piglets to develop gastrointestinal tract and immune functions in order to help with the transition period. Although research to confirm this hypothesis is ongoing, there is enough evidence to suggest that supplementing with nucleotides may positively impact piglet growth and intestinal integrity. It is important to note that most nucleotide-rich products are extracts of yeast fermentation and, therefore, may contain other active compounds (e.g. β-glucans and peptides) that may influence the response.

Conclusions. Reduced growth performance and the associated enteric diseases, such as diarrhea, are major concerns in the period immediately after weaning that lead to considerable economic losses to the swine industry. The historical practice of using antibiotics in the nursery phase to overcome these challenges is coming under increasing scrutiny for fear of its contribution to antibiotic-resistant bacteria, which in turn compromises human health.

To minimize production and economic losses associated with the removal of antibiotics, a large number of alternative feed additives and feeding strategies have been proposed. While there is plenty of research to support the use of some of these additives in post-weaning diets, further research is clearly necessary to better understand how these additives can be used effectively, whether individually or in combination where they might act synergistically to maximize benefit. BP

Source: Nyachoti, M. 2013. Nutrition and Gut Health in Piglets. Presented at: A Global Exchange of Ideas on Eubiotics in Swine, Eubiotics Focus Group meeting, Kansas State University, Manhattan, KS. April 16–19, 2013.

Janice Murphy is a former Ontario agriculture ministry swine nutritionist who now lives and works in Prince Edward Island.