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A Balanced Diet Is The Key To A Healthy RumenA Balanced Diet Is The Key To A Healthy Rumen

- Oct 24, 2018 -

A balanced diet is the key to a healthy rumen

The rumen is the most influential digestive site, and microbial fermentation provides most of the energy needed to maintain physical condition, pregnancy and lactation. Therefore, feeding rumen microorganisms and stabilizing the rumen environment are key.

The rumen ecosystem consists of four groups of microbes: bacteria, protozoa, fungi and archaea. There are also some phage, mycoplasma and ancient phage (Tapio et al., 2017). In terms of quantity, bacteria are by far the most abundant (Kim et al., 2011), 1010-1011 cells/ml, followed by archaea (106-108 cells/ml), protozoa (105 cells/ml) and fungi (103 ). -105 cells / ml). Bacteria account for about two-thirds of rumen microbial biomass, and protozoa account for 50% (Tymensen et al., 2012), mainly due to their size. This microbial ecosystem produces energy, nitrogen and other nutrients through the breakdown of dietary components.


Yeast cultures based on Saccharomyces cerevisiae have a positive impact on animal performance, milk yield and digestibility. Photo: Shutterstock

Volatile fatty acids (VFAs) are the end products of carbohydrate fermentation and are absorbed by the rumen wall as the main source of ruminants. It is well known that diets of high soluble carbohydrates (starch and sugar) can cause excessive production of VFA, particularly propionate and lactate, and ultimately lead to rumen pH and subacute acidosis (SARA) and/or acute acidosis. Cellulolytic bacteria survive in a relatively narrow pH range (6.0 or above; Russell and Wilson, 1996) in a relatively short period of time below this range, and then their growth and activity are compromised. Therefore, if the rumen pH is kept low for a long time, fiber digestion is inhibited. Subacute ruminal acidosis is a complex metabolic condition of cattle that involves a low rumen pH for a prolonged period of time. It is known as a long-term pH below 5.5 (Plaizier, 2008). The absence of a consensus threshold pH is a definitive diagnosis of this syndrome, and SARA is not only an acidic rumen environment, but also highly dependent on rumen VFA. Therefore, it is not only a pH-dependent pathology, but also a result of changes in the microbial population secondary to diet types (Calsamiglia, 2010).

Diet should be balanced

Rumen bacteria have different requirements for protein sources. Fiber digester requires almost no soluble nitrogen, ammonia. In order for microorganisms to effectively use such nitrogen sources, they require energy and this energy is provided in the form of fermentable carbohydrates. The synchronization between soluble nitrogen and energy supply has long been the subject of many regional ruminant diet formulations, with the goal of avoiding periods of excess or insufficient nitrogen supply. Even with full-mix diet (TMR) feeding, there is an excessive period of time, followed by a period of insufficient rumen ammonia levels.

This is especially true when the diet is supplemented with urea. Excess rumen ammonia is wasted and can cause an increase in blood urea nitrogen (BUN) and subsequently an increase in urea nitrogen (MUN) levels. Excessive supply of rumen ammonia may also result from over-fed dietary protein. Although recent studies have shown that if the diet is properly balanced, the diet is often formulated as 18% or 19% crude protein, which is unnecessary and may have an adverse effect on performance. Deamination and metabolism of excess protein results in energy expenditure in the animal, which may exacerbate the negative energy balance (NEB) of fresh cows. An increase in NEB in fresh cows also affects circulating progesterone levels, resulting in decreased reproductive performance (Tyrrell et al., 1970; Butler, 1998). This harmful effect can be mitigated by adequately balancing the energy and nitrogen supply of the microorganisms to avoid excessive dietary crude protein levels. The use of feed ingredients designed to meet the nitrogen requirements of about 95% of rumen microorganisms can help provide a balanced diet.

Live yeast is an anaerobic environment

Most beneficial bacteria in the rumen rely on a stable anaerobic environment to function; therefore, oxygen entering the rumen associated with feed pellets poses a continuing threat. The live yeast diet contains a rapid anaerobic environment that helps the ideal fiber digestive microbes to proliferate and effectively colonize feed pellets and results in lower rumen lactic acid concentrations, higher total pH and reduced risk of acidosis. Live yeast works by metabolizing excess oxygen that enters the rumen through the feed particles, helping to maintain the anaerobic rumen environment. There is also stimulation with bacteria that utilize lactic acid, which helps to reduce the acid load in the rumen and avoid a significant drop in rumen pH, which is detrimental to sensitive cellulolytic bacteria. These cellulolytic bacteria then thrive and produce VFA, which is then absorbed through the wall. This allows for a more efficient and complete digestion of the ration. In particular, the fiber fraction leads to an increase in feed efficiency (Fig. 1).


The promotion of cellulolytic bacteria results in the conversion of VFA to acetate, which results in the production of milk fat. In addition to scavenging oxygen, small peptides and cofactors produced by live yeast stimulate bacterial growth. The range of stimulatory compounds or metabolites produced by different yeast strains varies widely (Kondo et al., 2014), which contributes to some of the different responses of individual strains. Fatty acids, sugars and amino acids account for a large proportion of these metabolites, but the concentrations produced in yeast are very different (Kondo et al., 2014). This overall stimulating effect of live yeast not only increases feed utilization and digestion, but also drives dry matter intake (DMI), which is often seen to increase after the food contains yeast. Early studies with live yeast showed the effect of Holstein cows on milk production and composition.

In conclusion

Ultimately, the rumen is a fairly unstable fermentation vessel that relies on a close relationship with various microorganisms. Most beneficial bacteria in the rumen rely on a stable anaerobic environment to function, so both oxygen and acid are threats. Microorganisms also rely on the supply of energy and nitrogen, and can mitigate the deleterious effects of excess nitrogen by adequately balancing these supplies and avoiding excessive dietary crude protein levels. Live yeast is known to scavenge oxygen and produce irritating compounds that have beneficial effects on the rumen ecosystem and subsequent animal performance, although their efficacy varies widely.

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