In my opinion, there is no an ideal amount of bicarbonate that can be used as a supplement in dairy cattle. It will depend on the dietary component, the physicochemical properties of the rumen fluid and the animal’s physiological response.

There are two seminal articles from Russell and Chow (1993) and Kohn and Dunlap (1998) that deal with this topic. You can also look at my work for some ideas about this phenomenon, which it is still a work in progress.

A diet rich in carbohydrates most like will generate enough CO2 by fermentation to sustain a high HCO3- environment. Similarly, as VFAs are absorbed in exchange with intracellular HCO3-, there is a large HCO3- amount secreted into the rumen daily. Then, the oral addition of HCO3- will not have substantial impact on the ruminal buffer capacity.

However, there is another element that made the addition of this buffer of benefit in highly intensive system which is sodium… but that is another story.

The ideal dose different according to the bw and age of cattle

I agree to disagree,

This is the Herderson-Haselbalch equation in relation to CO2 species equilibrium.

pH = pka’ + Log [HCO3-]/[dCO2]

The equilibrium of CO2 species in a solution is pH dependent. In fact, under pH ~5.6 bicarbonate doe not longer exist in solutions. That is: all CO2 is in dCO2 form.

Therefore, If you are looking to supplement with bicarbonate salts, to cattle fed diets prone to subacute ruminal acidosis (SARA), You might find that the addition of bicarbonate in these diets might not have the value that you are expecting.

By definition cattle suffering with SARA low ruminal pH (below 5.8) for extended postprandial periods.

However, it is not the pH that made them sick or the lack of HCO3- under that pH. It is that all CO2 in the fluid, including HCO3- , it is in dCO2 form and readily available for absorption. If you supplement additional HCO3- it might not be enough to change this fact.

I.e. These two solutions have exactly the same pH (~6.1), but in the later the dCO2 concentrations 10 times greater and highly toxic for cattle.

pH = pka’ + Log [10]/[10] and pH = pka’ + Log [100]/[100]

Moreover, as the physicochemical properties of the fluid change during digestion, i.e. viscosity. Those changes impair dCO2 effervescence from the fluid causing long spells of high ruminal dCO2 or CO2 holdup.

The longer that cattle suffer of this condition the higher the risk of clinical signs of SARA. In fact, the clinical signs of SARA are the same as CO2 poisoning: lethargy, inappetence, respiratory and metabolic acidosis, etc.

The formula above also explain why pH does not always explain SARA. Although pH can be low, dCO2 concentrations might not be high enough to produce disease, cattle per see have developed a high tolerance to CO2.

Coming back to the question on hand. I am not saying that the addition of sodium bicarbonate does not have an effect, but it is unlikely that the amount that you add in the diet, under those conditions, will have any impact on bicarbonate and buffering capacity. Even if we take in consideration the cow weight, age and feed intake.

Really interesting, I do agree that in real clinical practice we find this difficulty of inefficacy of any amount of bicarbonate addition. But could you please suggest the alternatives to reduce CO2 hold up? The ruminal microbial manipulation?

What a great question.

I am still looking at it. However, I would like to described a little experiment.

Take two glasses one with carbonated water and another one with beer. Similar volume.

The differences between solutions explain CO2 holdup in the rumen. On the carbonated water you will see that bubbles are big and the quickly leave the glass. On the beer glass the bubbles are smaller and leave the solution very slowly.

The beer is like the rumen fluid. CO2 holdup: the dCO2 cannot easily leave the solution due to the physicochemical properties of the more viscous fluid. This effect limits bubbles formation and release (effervescence).

Now add to both solution sodium bicarbonate. you will see that the gas escape very quickly from both of them. In the carbonated water fizzles. But in the Beer it will form foam. This is the mechanism on Bloat and Abomasal dysplasia in cattle. You have destabilized the solution and CO2 will quickly be released leading to tympanism.

Do the same this time with NaCl and you will see the same effect as with sodium bicarbonate. This phenomenon call salting out the CO2 from the solution. And it is not an effect of bicarbonate, both solutions are saturated with HCO3-, but the Na which added to the liquid provides a substrate for nucleation (formation) of bubbles.

So, the answer is to add Na, the bicarbonate is the vehicle and a good one. Cl- might not be that desirable. how much? if your risk of acidosis is high add more to the diet. Here a good reference for a dosis/effect. (10.3168/jds.S0022-0302(97)76163-0)

I will also add that any compound that serves as a substrate for nucleation will have a good effect on preventing ruminal acidosis. Zeolites for instance are a good additive. But also, might be common sand.

Something that you might want to investigate.

Thanks for taking time to explain with an easy example. It gives more insight to what really happens when the buffer is added. In severe bloat here we try the mineral oil, there are certain commercial preparations too available for acute cases and they do show some relief. But I am more concerned with the SARA like conditions and the maintenance of rumen pH for maintaining efficiency, ameliorate stress impact etc. As you rightly pointed out something to investigate and learn. Went through some of your works, really appreciate, thanks.

Thank you very much for reading my work and discussing this topic, which I am passionate about.

I hope you did not get confuse. It is the same mechanism. CO2 holdup is the cause of all those syndromes. As I explained in my literature review.

If you want to control acidosis, you have to control postprandial CO2 holdup. The addition in the diet of compounds that improve CO2 nucleation might stop CO2 poisoning during acidosis.

Sorry that I cannot give you a specific answer about what is the best treatment. But now that I think I found the cause, better treatments can be developed.

Would you agree? All the best.

I do agree, knowing the science and understanding the problem in its real dimensions precedes recommending solutions. It is clear to me that the CO2 hold up is the real issue here and CO2 nucleation is one of the solutions that may help. Hope I am there!

In empirical treatments of such conditions soda bicarb is prescribed along with Mag carb and Barium carb. Probably barium carb which is insoluble may be helping in nucleation.(very farfetched assumption). Also I am tempted to mention that Soda bicarb and Ginger juice mix are common farmer remedies. Mud may also help but as a routine , I don't feel like recommending to any animal.

Thanks for the discussion

Best wishes