Feeding yeast to improve rumen efficiency and health

With the aim of developing firm ideas on when best to feed yeast and in what quantities, scientists are working hard to better understand the health and production benefits of feeding yeast.

Speaking at a conference last week organised by Lesaffre Feed Additives (LFA) in Lille, France, Jamie Newbold of Ibers, Aberystwyth, said the benefits of feeding live saccharomyces cerevisiae were well documented.

Scientists were also beginning to understand why these benefits came about.

“The rumen is continually challenged by oxygen,” said Prof Newbold. “That oxygen, while it’s there, is toxic to the bacteria. Yeasts can make the rumen environment less toxic to the bacteria and that increase in bacteria viability drives all of these other benefits.”

Further research was challenging because the levels of oxygen in the rumen, while being significantly reduced by feeding yeast, were still too small to be easily measured. While progress was being made, Prof Newbold and his team were also working to find out which bacteria yeast stimulates.

This research was ongoing, but already suggested yeast stimulated lactate utilising bacteria (increasing rumen pH) and fibrolytic bacteria (increasing fibre digestion), which in turn had the additional benefit of limiting the growth of starch-utilising bacteria.

Using sodium bicarbonate as a buffer instead of yeast stimulated fibre-degrading bacteria, but not lactate-utilising bacteria.

Prof Newbold said the aim was to know how yeast functions in different nutritional situations. “We want to be able to say ‘You have x ration, use y grams of yeast’,” he said.

Why does yeast benefit cows?

• The rumen is full of micro-organisms, including bacteria, protozoa, fungi and achaea
• Rumen bacteria work best in anaerobic conditions (in the absence of oxygen)
• While the rumen is largely anaerobic, some oxygen does get in - partly from food and saliva, but mostly from the blood in the thousands of blood vessels that profuse the rumen
• The rumen works to reduce oxygen levels, but this takes time
• Yeast ‘scavenges’ oxygen, more quickly, restoring an anaerobic environment
• This changes the microbial population, increasing bacteria’s viability and activity, resulting in increased degradation and digestion of feed, including fibre
• The benefits of yeast include a higher pH (less acidic, so less acidosis), more volatile fatty acids, increased digestibility and higher dry matter intake