Probiotics and prebiotics for calves

There is some confusion in the marketplace as to what constitutes a probiotic or prebiotic and what these terms mean. The market for probiotics and prebiotics is considerable and growing, with declining acceptance of antibiotics in animal feeds and milk replacers.

The World Health Organisation (WHO) defined probiotics as; “live microorganisms that when administered in adequate amounts confer a health benefit on the host”. The most common micro-organisms used in probiotics are Lactobacillus species and Bifidobacter bifidis bacteria, although other minor bacterial species and yeasts may be present in some probiotic formulations. Lactobacillus species and Bifidobacter bifidis are generally regarded as the main probiotic components for human and animal use.

Prebiotics are selectively fermented, dietary ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health. Unlike probiotics, prebiotics target the microbiota already present within the ecosystem, acting as a ‘food’ for the target microbes with beneficial consequences for host. Prebiotics are currently being discussed by working parties of international scientific organisations such as the Food and Agriculture Organisation of WHO and the International Life Sciences Institute, and changes to the definition and concept may follow in time.

Three criteria are required for a prebiotic effect:

  • Resistance of the prebiotic to degradation by stomach acid, mammalian enzymes or hydrolysis;
  • Fermentation (breakdown, metabolism) of the prebiotic by intestinal microbes; and
  • Selective stimulation of the growth and/or activity of beneficial microorganisms in the gut.

According to the International Scientific Association for Probiotics and Prebiotics, there are no probiotic standards in effect, making it difficult to define what is or isn’t a probiotic. However, there are guidelines in relation to the most common form of liquid probiotic, being yoghurt. The US National Yoghurt Association requires a minimum count of 100m cfu/g at manufacture and 10m cfu/g at expiry. (1m cfu/g is 1 million colony forming units per gram). Yoghurts have a relatively short shelflife; typically up to one month from date of manufacture. The majority of probiotics used in human and animal supplements are freeze-dried powders typically containing at least 10 billion cfu/g.

A search of the literature on probiotics indicates that survival of probiotic bacteria is a significant challenge in any medium. Best results are generally obtained through refrigeration, freezing, freeze drying or encapsulation techniques. Storage of probiotic bacteria in an aqueous medium at ambient temperature is likely to result in low survival. Even refrigerated yoghurts will only maintain probiotic bacteria at an acceptable level for several weeks. There do not appear to be any data supporting the use of unrefrigerated liquid mediums as a means of maintaining probiotic survival.

In March 2008, the International Probiotics Association established guidelines for probiotic labelling requiring:

  1. Clear identification of the probiotic bacteria and strain present
  2. Colony Forming Unit (CFU) count at the time of expiration (guaranteed minimum) of the product.

However these guidelines are not binding and there is no requirement for companies supplying probiotic products to comply with them.
A number of products sold in New Zealand as probiotics have ACVM registration. This is not necessarily a requirement for oral nutritional compounds, but will indicate the product satisfies New Zealand Food Safety requirements for toxicity, safety, and residues. Registration does not relate to, or endorse, claims of efficacy or stability for these types of products. Efficacy is only considered by ACVM for products that make therapeutic label claims or where there are animal welfare or trade considerations.

In summary, there are a large number of products in the market, with a multitude of claims and trials. When determining which product to use one should identify the specific active ingredients, their concentrations, modes of action and data supporting product claims.