Benefits of probiotics in ruminants
Live yeast is one of the most important probiotics used in ruminant nutrition. Over the last 30 years, our knowledge on the role of yeast in animal nutrition has been presented in the form of scientifically proven arguments. Considerable research has been published which reviews the major milestones that have helped to define the action of live yeast in ruminants.
According to Jouany in 2000, the number of published papers on probiotic yeast for ruminants increased rapidly from 1950 to 2000 resulting in around 80 papers published per year in peer-reviewed journals. From 1950 to 1980, much work was devoted to show improvements in animal performance and animal health with yeast supplementation.
Further research efforts gave a better insight on the understanding of basic mechanisms and modes of action in the 90’s.
Nowadays, in the advent of new fashionable biotechnological techniques, a more precise view on microbial activities and functionalities can be acquired. The ultimate goal however, is to define the application and production strategies that can optimise the animal’s response to probiotic yeast supplements. In this context, much effort is still needed to link research advances to what is in fact happening in field conditions.
The most obvious example is ruminal acidosis, a frequent digestive disorder in ruminants that causes health problems leading to substantial deterioration in productivity. According to an extensive literature review, the definition of acidosis is still unclear. Scientists around the world give their own description and definition of the acidosis which basically originates from an accumulation of strong acids in the rumen due to the consumption of a large proportion of readily fermentable carbohydrates by the animal. As it is chemically admitted, acidity of any given milieu is generally evaluated by the measurement of pH. Based on this fact, different thresholds (by different researchers, from different countries) have been established to first diagnose ruminal acidosis and then classify into whether it is sub-acute, sub-clinic, sub-chronic, latent or acute, clinic or chronic acidosis. Mean threshold pH values and pH drop against time have been, for a long time, the sole indicators of ruminal acidosis. As a result, these definitions are more experimentally-based than what can be perceived from the field.
Ruminal Redox potential (Eh) is more and more recognized as a suitable and complementary indicator to pH. Recent research studies showed that live yeast used as a dietary feed additive for dairy cows present an intrinsic capacity to prevent a drop of ruminal pH and reduce the Eh level. This ability enables probiotic live yeast to be another potent modulator of ruminal Eh. Live yeast supplementation via the modulation of ruminal Eh can be a good means to stimulate adequate microflora for better digestive efficiency of the diet. However, its effect on ruminal reducing conditions appeared strongly influenced by the level of the original reducing status induced by diet. Future research works may be directed to produce and select appropriate yeast strains with respect to their reducing capacity for use as feed additives in ruminant diets.
Lactic acid consuming bacteria such as Megasphera elsdeneii have been used to prevent acidosis in ruminants, but their use is at the moment limited. Propionibacterium should also be considered as interesting to maximize the proportion of propionic acid produced within the rumen.
Most of the other bacteria (lactic acid bacteria, bacilli) are used in a “classical way” to prevent development of pathogens by competitive exclusion and modulation of immunity, especially in young animals (calf, lambs, kids).
With increased concerns regarding antibiotic resistance in the human population, sustainable use of antibiotics will be examined and probiotic alternatives with proven effects are expected to be more and more frequently used for ruminants.