Antibiotics have been in use even before World War 2. These drugs played an important role in curing disease in both humans and animals. After the war, experiments showed that low, sub-therapeutic levels of antibiotics could increase feed efficiency and growth in food animals. Since then, the addition of various antibiotics to animal feeds is routinely done. Because prevention of disease transmission and enhancement of growth and feed efficiency are critical in modern animal husbandry, there has been widespread incorporation of antibiotics into animal feeds in many countries. But recently, in some countries, including European Union countries, the use of sub-therapeutic levels of antibiotics in animal feeds has been restricted, thus the need for alternatives.
Bacteria are ubiquitous and are very adaptable microorganism due to their very short generation interval and their ability to share genetic information. The use of antibiotic may kill most bacteria but the resistant strains may be able to re-establish themselves. They may also be able to share their resistance in their genes to their succeeding generations or to other species of bacteria. This has been observed both in human and animal patients. So there is a danger in the transfer of disease causing organisms from animals to humans who consume the animal products. The possibility of having antibiotic residues in the animal products is also potentially dangerous since the humans who will consume such products would also be receiving sub-therapeutic dose of antibiotic. Among the known antibiotic resistant strains of bacteria include Salmonella, E. coli, and Campylobacter. They have been isolated from farm animals.
The exact mechanism on how antibiotics promote growth is not completely known, although there are some hypotheses. Since feed antibiotics provide a relatively greater improvement in farms with poor hygiene, their effectiveness is partially due to suppression of some pathogenic bacteria in the animals. Antibiotics also alter the microflora of the gastrointestinal tract which may have an effect on digestive processes and thus on the utilization of nutrients in the feeds. An example is the decrease in energy loss due to microbial fermentation in the gut because of reduced gut bacteria. This extra energy will be of use to the animal. Antibiotics also inhibit the inactivation of pancreatic digestive enzymes caused by bacteria because bacterial growth is decreased.
With the recent trend in the reduction of use of antibiotics as growth promotant, the search for alternatives has been going on and has been subject of numerous researches. The possible alternatives to antibiotics as growth promotant must be able to replicate the effect of antibiotics which are: increased growth, improved feed efficiency and lower incidence of diseases. It must also be cost efficient so that it would actually be used by farmers.
Probiotics can be possible replacement. They are live cultures of microbes which are fed to animals to improve health and growth by altering intestinal microbial balance. Most commonly used are lactic acid bacteria but some other species are also used. Some also consider extracts of these cultures, for example isolated yeast cell walls, to be probiotics even though they do not contain living cells.
Some bacterial cultures are used specifically for competitive exclusion. They are fed in one or a few doses to newborn or newly hatched animals in order to quickly establish an intestinal flora that will prevent colonization by pathogenic bacteria later on in the life of the animal.
The possible mechanisms being explored in the use of probiotics are numerous. One is that they adhere to the intestinal mucosa and prevent attachment of pathogens (competitive exclusion). Another is the production of antimicrobial compounds such as bacteriocins and organic acids. They are also hypothesized to compete for nutrients with the pathogenic ones. They are also able to stimulate and enhance the immune response of the intestines.
There are many published researches on probiotics but responses are varying but most are encouraging. They are noted to decrease mortality in piglets especially on farms with prevalent digestive diseases, but they may not be able to exert their effect under all conditions so use is on a case to case basis. Here in the Philippines, the limiting factor is the price and availability. They generally cost higher than antibiotics and are not available in large volumes for application in large farms.
Exogenous enzymes are currently gaining popularity in the feed industry. These are enzymes that are added to feeds of pigs and poultry. Although a variety of gastrointestinal enzymes are naturally present to aid digestion in animals, their young may produce inadequate amounts of certain enzymes. Even adult pigs could not digest some plant materials containing complex carbohydrates and phosphorus. So these enzymes are used to supplement the animal’s own digestive enzyme activity and to make use of the materials that are just being excreted by the animal.
Phytase can release 50-75% of the phosphorus being bound by phytate. This means reduction in the use of inorganic phosphates which generally are not very digestible. Use of phytase effectively reduces environmental pollution because most of the organic phosphorus in the diet is absorbed by the animal’s body. Phytase decreases by as much as 30% the phosphate excretion. Enzymes for carbohydrates are also available such as amylase, glucanase and glucoamylase with promising results. They have been shown to improve feed conversion and decrease incidence of diarrhea in young pigs.
The efficacy of enzyme additives appears to depend on several factors such as weaning age, diet components, and enzyme source. Enzymes are also heat sensitive so heat-resistant enzymes must be used especially on heat-treated feeds such as pelleted feeds.
Immune modulators can also be used as growth promotant. They are compounds that affect the immune system which may enhance resistance of animals against diseases. These include antibodies, cytokines, spray-dried plasma, and other similar compounds. They may exert similar response as that of antibiotics. The use of these may mimic the effect of vaccine and colostrum which are helping the animals fight off infection.
A concern here is that these compounds are strain-specific, which means that each farm may have a different requirement. Something may work well on a farm but may not be able to elicit the same response on another because of innate differences in their microflora. Another concern is the observation in some researches that they obtain better results in stressful and less hygienic conditions like the results that are usually obtained in using antibiotics.
Organic acids are also gaining popularity as growth promotant in swine and poultry. Organic acids contain one to seven carbon atoms and are widely distributed in plants and animals and are usually produced during microbial fermentation. They are used to decrease the pH of the gastrointestinal tract of the animal being fed. With low pH digestion of proteins and populations of beneficial bacteria are maximized, and harmful bacteria are inhibited. Some authors speculate that their effects are not simply a result of acidification but rather on the increase of beneficial organic acid ions and the resulting reduction in the population of bad bacteria in the gut.
Researches show that among the organic acids, fumaric acid is better used in young piglets and formic acid is more effective in fattening pigs.
A concern in the use of these acidifiers, especially the organic ones is that they are expensive. A less expensive way of acidifying feeds is via fermentation which may be done using a mother culture in the farm or by using by-products which are easy to ferment such as food factory by-products.
The other noteworthy supplements that have growth promoting properties are zinc or copper, vitamin E, conjugated linoleic acid, carnitine, amino acids and herbs. Zinc and copper are minerals and are best added to piglet feeds singly and not together because their effects are not additive. Zinc also traduced incidence and severity of diarrhea in piglets. Vitamin E can reduce weanling diarrhea while conjugated linoleic acid can increase lean tissue and weight gain. Carnitine if added on the diet can improve growth, increase piglet survival (if given to sows) and weight gain. Synthetic amino acids, on the other hand, can be used in a strategy to decrease the crude protein of the feeds and in effect level out the available limiting amino acids, thus preventing overages and decreasing the cost of feeds. Herbs or mixture of herbs are also gaining popularity, although they are generally expensive and not available in large quantities for use commercially. Most have antibacterial effects but the most obvious effect is the improvement in palatability which increases pig intake.
Among the ways of reducing antibiotic use in feeds, the employment of alternative husbandry practices is the most cost effective and most sound. With this, one must go back to the basics and provide the best in everything needed in the life of the animal. Examples are efficient cleaning methods, appropriate ventilation rate, appropriate environmental temperatures, appropriate environmental temperature, optimum stocking rate and proper record keeping to immediately identify problem areas. If implemented, this would effectively decrease reliance to antibiotics.