Merck Manual

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Professional Version

Probiotics for Animals

By

Zachary K. Smith

, PhD, South Dakota State University

Last full review/revision Apr 2022 | Content last modified Jun 2022

Probiotics promote the establishment and development of a desirable intestinal microbial flora balance.

Although benefits of probiotics to animal growth performance are variable, the benefits to aspects of food safety are more consistent and favorable. Many compounds have been investigated in recent years that can lower incidence of Escherichia coli and Salmonella prevalence in production animals. For example, Salmonella can infect the GI tract of animals at a variety of time points in production. Pathogenic bacteriacan proliferate in the GI tract and subsequently take residence in various lymph nodes and within the GI tract where it can then contaminate meat products on harvest. Many animals may harbor and shed these pathogenic bacteria but remain clinically normal; however, there is still the risk of decreased feed intake and growth performance in these cattle infected with these pathogenic bacteria that are sensitive to probiotic supplementation.

Currently, many antimicrobial alternatives are being investigated to determine their pre-harvest efficacy to reduce foodborne pathogens. There is a delicate balance between normal and pathogenic microorganisms that reside within the GI tract of the animal. This balance can be upset by poor husbandry conditions, disease, or stressors (eg, transport, meteorological conditions, lack of food, and improperly stored feed). Bacteria that produce lactic acid can, in general, be beneficial to the animal; certain yeasts may also be beneficial. Their ability to increase growth and promote health are claimed to be due to one or more of the following factors: preventing colonization of the gut by pathogenic coliforms such as Escherichia coli and Salmonella, altering GI absorption rate and extent of nutrients, and inhibiting pathogenic bacterial growth and influencing the balance of beneficial bacteria in the gut.

The probiotic feed additives consist of selected strains of lactobacilli and streptococci that alter the microbial species present in the GI tract to the benefit of the treated animal. Unicellular yeasts are also used in animal production. The production benefits are highly variable, and positive responses are more likely when a stressful management change occurs that may result in a change in balance of the gut microflora. Thus, they are useful in some cases to minimize gastrointestinal upsets or to help overcome stress due to weaning, transport, or adverse weather conditions. The unicellular yeast fungus may also have beneficial effects on rumen fermentation parameters, thereby improving digestion and subsequently improving feed conversion efficiency. The effect of probiotics in older animals may be decreased because of the well-established, balanced population of microflora that is less sensitive to minor detrimental husbandry challenges that animals may endure (eg, the stress of weaning or transportation).

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