Strategies for reducing antibiotic use in chickens

On a long-term basis, the increased costs of alternative methods to prevent disease are compensated for by the advantages gained when the use of antibiotics in the poultry industry is reduced – something which makes such alternatives economically justifiable.

Studies have shown that antibiotic treatment in chickens affected serum biochemical parameters and exhibited an abnormal appearance in the liver and minor atrophic changes in the kidney. Examination of the liver, kidney and intestines revealed the presence of notable changes in their histological structure. Self-medication in poultry farming impacts both avian and human health and veterinarians should focus their attention on combating self-medication in poultry farming, in particular, antibiotics.

Antibiotics may also affect soil function and plant composition. In soils exposed to the manure of antibiotic-treated birds, there are often negative effects on micro-organisms involved in normal soil processes, such as nitrification and organic matter decomposition. When planting crops such as corn, potatoes, lettuce and other crops intended for human consumption, there is an uptake of antibiotics by the plant tissues, reaching concentrations of about 0.1 to 1.2 ppm on a dry weight basis. Although such concentrations are not toxic, over time, this may increase the development of antibiotic resistance in humans consuming these crops.

Most importantly, the overuse of antibiotics over time can contribute to the spread of antibiotic-resistant bacteria – sometimes called ‘superbugs’ – as they move from farms into the surrounding environment and onto meat found on grocery store shelves, thus endangering public health.

Nutritional strategies

With most disease outbreaks, it may be necessary to increase the level of dietary protein or at least maintain it within the recommended ranges. Protein is a potent regulator of hormone circulation, for example insulin, glucagon, thyroxin and growth hormones, all of which affect the immune system and hence improve its disease-fighting capability.

An adequate calcium-to-phosphorus ratio in rations reduces the incidence of infectious diseases. There is also a relationship between resistance to infection and administering supplements with specific trace minerals, such as zinc, copper and iron, which promote optimal immune cell function, again, resulting in a decrease in antibiotic use.

Vitamin A and its precursor, ß-carotene, are necessary for the proper functioning of epithelial cell membranes and the immune system. Vitamin E with selenium is also important as it acts as an antioxidant defence against oxidative damage and has therapeutic value in cases of infectious diseases, by increasing the intracellular killing of ingested bacteria.

Plant extracts

Extracts of plants, such as cinnamon, Mexican pepper, thyme and aged garlic, have been recently exploited in poultry nutrition. These agents have been successfully applied to disease models of poultry at 100 μg/ml and can have antibacterial properties at costs comparable to the antibiotics themselves, with fewer risks to the birds, humans and the environment.

Further studies have shown that grape seed extracts, used in poultry diets at 125 to 250 ppm, have powerful antimicrobial properties due to their abundance of phenolic compounds. These compounds are capable of killing a wide variety of protozoa, bacteria, yeast and some viruses, as well as treating parasitic infections. In addition, dietary grape seed extract can replace synthetic antioxidants and be utilised to increase vaccination effectiveness. In terms of performance, it was found that the inclusion of grape seed extract in diets at the said concentration resulted in an increase in body weight gain of broiler chickens from 58.3 to 60.9 grammes per day from 0-48 days of age, with a similar feed intake.

Butyric acid

The inclusion of 300 ppm and 400 ppm butyric acid may have beneficial effects on poultry performance or health by decreasing the incidence of subclinical necrotic enteritis caused by C. perfringens and stimulating the growth of beneficial gut bacteria. Butyric acid also has anti-inflammatory effects and has been shown to strengthen the gut mucosal barrier by increasing the production of antimicrobial peptides in mucous and stimulating the expression of tight junction proteins. The acid also improves the feed conversion ratio in broilers and reduces fat carcasses due to stressors, through pro-inflammatory cytokines which have a positive effect on lipid metabolism.

Vegetable oils

Feed additives comprising capric, caprylic, lauric and linoleic fatty acids derived from vegetable oils, have also been used as an alternative to the use of in-feed antibiotics. These acids have a strong bactericidal effect and inhibit the growth of most pathogenic and opportunistic infections common among birds, including coliform, streptococcal, staphylococcal, salmonella and E. coli. They interact with hydrochloric acid, which activates the fatty acids and allows them to exhibit their bactericidal effect. The fatty acids are then absorbed into the blood like normal fat and are completely oxidised into energy without accumulating in the body. The birds getting this additive are completely protected from intestinal infections, which account for more than 99% of all diseases in birds.

Organic acids, such as citric or acetic acids, are also promising alternatives for growth promotion and disease prevention in poultry. They act by killing pathogenic bacteria and favouring the growth of certain acid-loving beneficial bacteria. Further studies have determined that in-feed enzymes, such as xylanases, are effective in decreasing intestinal lesions, thereby reducing the risk of necrotic enteritis in broiler chickens and the risk of certain diseases, such as colibacillosis in layers.

Ventilation, stocking density, biofilm, litter

Poultry houses and facilities should be located away from potential sources of infection and be easy to clean and disinfect. They should also be arranged to allow for batch-wise rearing (all-in/all-out) of birds. In addition, proper ventilation in a poultry house is critical to achieving good air quality which reduces susceptibility to respiratory infections.

High stocking density may restrict bird movement, interfere with airflow and increase litter moisture and microbial growth, including pathogens, which could potentially impair health, welfare and performance. When reducing antibiotics, the space per bird should be increased by 46 cm² per bird compared to the current conventional programme. This will help to keep litter moisture at a minimum thereby reducing the shedding of pathogenic bacteria over the population.

Separate materials should be used for each house, keeping a dedicated set of tools and equipment necessary for daily operations. No materials should be moved from one house to another unless they have been thoroughly disinfected.

The build-up of biofilm in waterlines may be an issue. Biofilms not only block the water flow but can also include pathogenic bacteria. These problems can be solved either by flushing the line to remove the detached biofilm, or by applying hydrogen peroxide at high concentrations, leaving it in the system for 24-48 hours to remove the biofilm from the pipelines.

Effective litter management is another step to keep birds healthy. Litter dryness and ammonia content at bird level are 2 significant key success factors in raising poultry. Litter treatment with acidifying or binding substances and adequate ventilation are the most practical measures to control ammonia and improve litter quality. Litter sanitation and treatments need closer attention when built-up litter is used.

The transition to animal farming with low use of antibiotics is a step-by-step process that must be carefully monitored. In the transition period, antibiotics should be used against bacterial diseases only and not for viruses. Using antibiotics for viral diseases is a waste of money and only contributes to the development of antibiotic resistance. Proper diagnosis of the cause of the disease by a certified veterinarian, therefore, is crucial to choosing the right treatment.