Understanding the Role and Differences of LIVE YEASTS
Feed conversion efficiency (FCE) is becoming an ever-higher priority for both dairy and beef producers, with many increasingly focused on the potential for better rumen function to improve overall efficiency, and boost margins over feed (MOF). With more accurate ration formulation and the fine tuning of nutrient supply to the rumen capable of achieving only so much, the role of yeasts, buffers and rumen conditioners has come firmly under the spotlight. However, for yeasts in particular, the way in which they work,
the benefits to the rumen environment, and the factors that determine efficacy are often not fully understood. And according to Dr Derek McIlmoyle, AB Vista’s EMEA ruminant technical director, that can turn decisions about when and where a yeast will add value into a lottery, with many missing out on the potential gains as a result.
Optimising rumen function “Yeasts have a really important role to play in high performance ruminant rations, but to get the best return on that investment it’s critical that the right type of yeast is used, delivered in a way that optimises efficacy, and in situations where the benefits will outweigh the cost,” he states. “The rumen functions best when conditions are both optimised for
fermentation that take place, and as stable as possible. For example, maintaining a pH that’s as close to 6.0 as possible is essential – fibre digestion is compromised any time pH drops below 5.8 or rises above 6.2 – as is ensuring conditions remain mostly anaerobic.” Because the rumen microbes responsible for fibre digestion are
anaerobic, any oxygen build-up in the rumen, such as when large quantities of rapidly fermenting feeds or acidic silages are fed, will quickly undermine fermentation efficiency. Not only is the activity of the fibre-digesting microbes restricted, but in severe cases the actual numbers present can be substantially reduced.
Re-establishing anaerobic conditions “Buffers and rumen conditioners are useful for re-establishing rumen pH within that ideal 5.8-6.2 range, and yeasts will have some effect on rumen pH. But that’s not their main function,” Dr McIlmoyle continues. “The research has shown that yeasts are capable of delivering
feed efficiency gains over and above those achieved by optimising rumen pH, by acting to improve overall conditions in the rumen. This is done primarily through the mopping up of excess oxygen, and
PAGE 26 MAY/JUNE 2018 FEED COMPOUNDER
by competing for sugars, which reduces populations of detrimental aerobic microbes and encourages proliferation of those anaerobic microbes responsible for fibre digestion.” Greatest effect from the addition of a yeast is achieved when that
yeast is intact, live and metabolically active (see Figure 1), and when introduced to a rumen where the pH is already close to optimum. It’s for this reason that greatest performance gains are often seen when a yeast and a rumen conditioner are used together.
Figure 1: Impact of different yeast types on fibre digesting rumen microbe populations (Source: Newbold et al., 1996)
Proven research results In one study carried out at the Schothorst Feed Research (SFR) in the Netherlands, the combination of an active live yeast and a rumen conditioner substantially reduced the time rumen pH was below the point at which fibre digestion is compromised (50 vs. 87 mins below pH 5.8) compared to using the yeast alone (see Figure 2). The trial, which used a small group of fistulated Holstein Friesians fed a 65:35 forage-to-concentrate ratio diet, also showed a significant increase in the proportion of acetate (63.0 vs. 61.4%) and butyrate (13.6 vs. 12.8%) volatile fatty acids (VFA) in the rumen.
Figure 2: Effect of active live yeast on rumen pH (Source: Schothorst Feed Research, 2014)
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