Enhanced Ruminal Fermentation Parameters and Altered Rumen Bacterial Community Composition by Formulated Rumen Buffer Agents Fed to Dairy Cows with a High-Concentrate Die

Authors: Sonny C. Ramos,

Chang-Dae Jeong ۱, Lovelia L. Mamuad, Seon-Ho Kim, A-Rang Son ۱, Michelle A.

Miguel, Mahfuzul Islam, Yong-Il Cho و  Sang-Suk Lee

Year of publication:2021

INTRODUCTION:

The use of high-concentrate diets for high-producing cows to meet their production and maintenance requirements is common practice. However, the use of these diets has drawbacks and can limit the animal from reaching its maximum genetic potential for milk production. One of the limiting factors is subacute ruminal acidosis (SARA).

Feeding rapidly fermentable carbohydrates can lead to the accumulation of short-chain fatty acids, a decrease in rumen pH, and ultimately changes in the microbial population. Due to the important role of the rumen microbial population in fiber digestion, changes in the microbial community can affect animal performance and health. For example, a decrease in rumen pH can reduce cellulolytic bacteria (fiber-digesting bacteria) and increase lactobacilli (acid-producing bacteria). Therefore, the use of buffering agents to stabilize the rumen environment and the volatile fatty acid ratios in high-concentrate diets is essential.

Saliva secretion in forage-based diets is an important factor in increasing rumen pH due to the longer rumination time; saliva contains abundant sources of bicarbonate and can act as an endogenous buffer. However, bicarbonates have limited buffering capacity because of their rapid solubility and short residence time.

Materials and Methods

In the study by Ramos and colleagues, the effects of buffers on rumen fermentation and bacterial parameters were investigated using both in vitro and in vivo methods. Their experiment was conducted on three cannulated Holstein Friesian cows in two phases. In the first phase, which was conducted in vitro, the effects of two buffer mixtures—including bentonite (BEN), calcium carbonate (CC), sodium bicarbonate (SB), sodium sesquicarbonate (SS), calcium oxide (CO), and processed coral (PC)—on rumen fluid were examined. In the second phase, the same buffer compounds tested in the first phase were evaluated in vivo as a combined treatment.

RESULTS AND DISCUSSION:

Sodium bicarbonate (SB) is commonly used to increase rumen buffering capacity to raise rumen pH in high-concentrate diets and help maintain milk fat content. Research has also shown that using magnesium oxide alongside SB can have beneficial effects on the diet. However, it is important to note that the supplementation of these two buffering agents should not exceed the mineral requirements of the animals (SB at 113 grams and magnesium oxide at 45 grams per day per cow). ​

Among the treatments tested, calcium oxide (CO) had the highest buffering capacity compared to the other experimental treatments and maintained the highest rumen pH throughout the experiment (it was the only treatment with a recorded pH above 6). The delay in the increase of rumen pH when using CO indicates that CO acts as an alkalizer. Alkalizers increase rumen pH and neutralize acid, whereas buffers prevent the pH from dropping. The reason for using buffers in high-concentrate diets is to reduce hydrogen ion concentration in the rumen. The hydrogen ions produced, when combined with bicarbonate, neutralize rumen acidity. The product of this reaction is water and carbon dioxide. Therefore, gas release in the environment can be considered a good indicator of hydrogen ion neutralization in the rumen.

In this study, compounds such as calcium carbonate (CC), sodium bicarbonate (SB), and sodium sesquicarbonate (SS), which are carbonate-based, had the highest buffering capacities after calcium oxide (CO). This is because the presence of carbonate affects acid production and establishes a better acid balance compared to other treatments. Sodium bicarbonate and SS, with similar functions, effectively neutralized rumen pH drops. These two compounds also showed the highest gas production levels. This indicates that the SB and SS treatments, along with increasing buffering capacity, did not inhibit fermentation, which could explain the lower pH observed in these two treatments. Sodium bicarbonate, due to its high solubility, produces a faster neutralizing effect on rumen pH but exhibited lower buffering capacity over 24 hours of incubation. By increasing rumen pH, sodium bicarbonate improved the performance of cellulolytic bacteria in fiber digestion. Subsequently, acetate production and its ratio to propionate in the rumen were affected.

An increase in rumen pH led to an increase in protein solubility. Therefore, as rumen pH increased, the proportion of ruminal NH₃-N also increased. This indicates that the ruminal NH₃-N proportion has a positive correlation with the production of volatile fatty acids (VFA) in the rumen.

In the second experiment, the metagenomic performance of the rumen bacterial population across 218 genera was also examined following the supplementation of buffering compounds. Firmicutes, Bacteroidetes, and Actinobacteria are the dominant microbial diversity in the rumen population. Among these, Firmicutes and Bacteroidetes are considered the main components of the rumen microbiome. These two phyla showed less sensitivity to sudden changes in the rumen ecosystem, especially acidosis. Bacteroidetes, which play a role in the digestion of structural carbohydrates, are eliminated under acidic conditions. Therefore, sudden changes in the rumen ecosystem are accompanied by shifts in the rumen microbial biome and alterations in digestive efficiency.

Conclusions:

Feeding high-producing cows with high-concentrate diets can harm animal health and reduce performance. Therefore, buffering and alkalizing compounds are needed to increase and stabilize rumen pH, preventing its decline. Generally, sodium bicarbonate is used to meet this need. Although this simple solution can be beneficial, to improve animal performance through the rumen microbiome, the correct mixture of buffering and alkalizing compounds should be used in order to take advantage of the benefits of both and minimize their drawbacks as much as possible.

REFERENCES:

https://doi.org/۱۰.۳۳۹۰/agriculture۱۱۰۶۰۵۵۴

Ramos, S., et al., Enhanced Ruminal Fermentation Parameters and Altered Rumen Bacterial Community Composition by Formulated Rumen Buffer Agents Fed to Dairy Cows with a High-Concentrate Diet. Agriculture, ۲۰۲۱. ۱۱: p. ۵۵۴.