Ruminal dCO2 monitoring: driving optimal Milk Yield and Quality
Positive Effects of High dCO2 on VFA Formation
Rumen fermentation is a complex process involving a diverse microbial community. Dissolved CO2 plays a crucial role in this process, influencing the activity and metabolic pathways of various bacterial groups (Caldwell et al., 1969; Dehority, 1971 ). Therefore, focusing on dCO2 determinations offers a direct connection to the availability of substrates for propionate producers.
High dCO2 environments benefit the production of VFAs, including succinate and lactate. These VFAs serve as essential substrates for propionate-producing bacteria. Two main pathways are involved:
Succinate pathway: Succinate is utilized by propionate producers to form propionate and CO2 (Paynter and S. R. Elsden, 1970).
Acrylate pathway: Lactate is converted to acrylate, which is then further metabolized to propionate (Wallnöfer et al., 1966).
Propionate Production and Milk Yield
Propionate is the primary energy source for ruminants and plays a critical role in milk production. Propionate is a gluconeogenic precursor and is converted into glucose by the liver. Glucose is a vital energy source for mammary gland tissue, ultimately contributing to milk synthesis (Aschenbach et al.,2010), especially lactose formation which drives the increase in milk yield. There is a positive correlation between ruminal propionate production, absorption and higher milk yield.
Milk quality is driven by an optimal acetate-to-propionate (A/P) ratio.
Let's not forget the other main milk components, fat and protein. They not only need energy in the form of glucose but also a steady supply of other key VFAs, acetate and butyrate (Elliot and Loosli, 1959). As fermentation shifts towards propionate production, a lower proportion of acetate might be found which is know to affect fat synthesis at the mammary gland.
See the following example below:
Russell’s work on A/P ratio look at the wrong factor
The graphics shown above were extracted from Russell's work in 1998, illustrating the "attributed" impact of pH on the A/P ratio. Interestingly, the distinct responses between the Hay and Corn diets suggest that the pH influence varies between the two. While a clear linear correlation between the A/P ratio and pH is visible in the Hay diet, this relationship is no longer evident in the Corn diet. This discrepancy suggests that pH is not really the factor influencing A/P ratio, as the effect should be consistent across all diets otherwise.
The true factor affecting the rumen's A/P ratio is CO₂ holdup.
Corn diets are prone to producing non-ideal conditions that lead to higher dissolved CO₂ (dCO₂) concentrations. These diets also produce higher HCO3- concentrations, thus the qoutient (pH) looks normal (~6.3 pKa1 of CO2). Conversely, hay diets promote more ideal rumen conditions, resulting in lower dCO₂ concentrations. In simpler terms, corn diets consistently exhibit higher dCO₂ compared to hay diets. However, in hay diets, high dCO₂ is only observed at low pH when the formation of dCO2 is enhanced.
Russell's results can be explained by CO2 holdup.
The close relationship between pH and A/P ratio in the hay diet is explained by the higher concentration of dissolved CO2 (dCO2) found at lower pH. This provides more precursors for propionate production. As propionate production ramps up, the A/P ratio drops, and methane formation also tends to decrease.
In the corn diet, with its high dCO2 concentrations regardless of pH due to CO2 holdup, the A/P ratio remains low, and so does CH4 formation. This is because there is always more substrate available for propionate formation.
The True Value of Monitoring and Manipulating Dissolved Carbon Dioxide (dCO2)
Accurately monitoring and strategically manipulating dissolved carbon dioxide (dCO2) levels in the rumen presents a significant opportunity to optimize ruminant health and production. By influencing dCO2 concentration, we can directly impact the rumen's acetate-to-propionate (A/P) ratio.
Optimizing the Rumen Environment Through Diet
The key to achieving this manipulation lies in tailoring the diet of ruminant animals to create the environmental conditions necessary for optimal ruminal bacterial function. Specific dietary components can influence fermentation patterns and dCO2 levels. For example, including readily fermentable carbohydrates can stimulate early rumen activity and dCO2 production. Conversely, providing adequate fiber promotes slower, more balanced fermentation, leading to a more stable dCO2 concentration.
Benefits of a Strategic Approach
By implementing these strategies, we can achieve a multitude of benefits:
Real-time dietary adjustments: Provides real-time information on dCO2 levels, allowing for immediate dietary adjustments to maintain a dCO2-rich environment.
Improved nutritional management by herd, groups and individual: Enables a more comprehensive understanding of the complex interplay between dCO2, VFA production, and overall rumen health.
Increased Milk Yield: A well-managed rumen environment with optimized dCO2 levels can enhance microbial activity and nutrient utilization, ultimately leading to higher milk production.
Improved Milk Quality: Optimal dCO2 promotes beneficial bacterial populations that contribute to desirable milk composition and fatty acid profile.
Reduced Methane Emissions: Effective dCO2 management can steer rumen fermentation towards propionate production, a pathway that competes with methane formation. This translates to a significant reduction in methane emissions from ruminant animals (Weimer, 1998).
The Milk Fat Depression (MDF) syndrome: a case for Ca2+ sequestration: MFD is a phenomenon consisting of a reduction in milk fat content below the expected values according to stage of lactation and production level, even to levels below milk protein content. Since CO2 Holdup also contributes to ruminal acidosis, the combination of a low A/P ratio and ruminal acidosis can lead to MDF.
There is two main prevail theories described for how MDF is triggered (Jordana and Anrique, 2015), which involves a direct inhibition of fat formation or short supplied of precursors. Both theories rely on the effect of ruminal acidosis, as it might reduce the availability of precursors, complex fatty acids and and VFAs (Jenkins, 1996; Russell, 1998).
My view is simpler. MDF occurs because a reduction in intracellular HCO3-, triggered by the effect of ruminal hyperosmolarity on H2O and CO2 transport, which can limit HCO3- formation within the cytosol. As low intracellular HCO3- becomes generalized, respiratory or metabolic acidosis ensues, which of course will mask this metabolic imbalance: the cellular responses is to ramp up H2O and CO2 formation in the mitochondria (anabolism). This step requires the activation of Ca2+ channels and the sequestration of intracellular Ca2+ into the mitochondria (Greiser et al., 2023). Diets depressing milk fat lower also the soluble Ca2+ in milk (Davies et al., 1983) and fat micelles size is intrinsically linked to the amount of free intracellular calcium (Couvreur and Hurtaud, 2016). Since fat micelles in the mammary gland require Ca2+ for secretion into milk, a cytosolic depletion of Ca2+ might leads to milk fat depression (MFD) syndrome.
Monitoring and optimising dCO2 concentrations
Manipulating rumen fermentation by promoting a dCO2-rich environment through dietary adjustments.
The ruminal dCO2 present in the fluid is an unique compartment, different to erupted CO2 or metabolised CO2 (breath), and cannot be measure indirectly.
Continuous dCO2 monitoring with our patented sensor presents a promising approach for improving milk production and reducing methane emissions in ruminant livestock.
This strategy can potentially contribute to a more sustainable livestock production system while enhancing animal performance and milk quality.
