Rumen Buffers, DCAD, and Enhancing Milkfat Production

Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University

Background

Enhancing milkfat production continues to be a vital and economically important goal for dairy farmers. Milkfat production is very responsive to a host of nutritional decisions, including carbohydrates, amino acids, and forage feeding. Other important nutritional decisions that affect milk fat production include managing the rumen environment through use of buffers or alkalizers and increasing the dietary cation anion difference (DCAD). The objective of this article is to review some scientific literature on buffers, alkalizers, and DCAD to help enhance milk fat production.

Feeding Buffers

The term ruminal buffer is used broadly in dairy nutrition, but it is not necessarily the most accurate term. Feed supplements that affect rumen pH can be categorized as true buffers or alkalizers. True buffers (i.e., sodium bicarbonate) resist changes in ruminal pH but they do not necessarily increase ruminal pH, while alkalizers may increase rumen pH (i.e., magnesium oxide). We’ll discuss these slightly different supplements as a broad category of feed additives to manage ruminal pH.

Sodium Bicarbonate

Sodium bicarbonate is one of the most prominent ruminal buffers fed to cattle, and there are a lot of data demonstrating its efficacy when feeding dairy cattle. One project supplemented 0.43 lb/day of sodium bicarbonate to lactating dairy cattle and increased the minimum rumen pH and reduced the time the rumen was less than 5.5 compared to a non-buffered diet. Another study demonstrated that feeding 0.40 lb/day of sodium bicarbonate increased rumen pH and dramatically reduced time with a pH <5.5; in the same experiment, sodium bicarbonate increased both milk fat concentration and yield. Reducing ruminal pH does not always occur though; Bach et al. (2018) subjected cows to increasing concentrations of barley while feeding sodium bicarbonate and did not observe differences in rumen pH or time spent with low rumen pH.

Providing the sodium bicarbonate increases milk fat concentration and milk yield (Cruywagen et al., 2015; Neville et al., 2019). A meta-analysis investigating sodium bicarbonate supplementation in dairy cattle suggests that providing approximately 0.45 lb/day of sodium bicarbonate per cow increases milk fat concentration and milk fat yield (Hu and Murphy, 2005).

Table 1.  Partial budget for feeding sodium bicarbonate at 0.45 lbs/cow/d in place of soybean hulls and assuming a 100 g/d increase in milk fat yield.

The question of sodium bicarbonate, like any other rumen buffer supplement, should come back to a return on investment. The increased milk fat in response to sodium bicarbonate ranged from 50 to 160 g/day, depending on the data cited. For our partial budget (Table 1), we’ll assume a100 g/day increase in milk fat when feeding 0.45 lb/day of sodium bicarbonate. The cost for the sodium bicarbonate was assumed at $610/ton, which results in $0.14/cow/day of ration cost. When including the soybean hulls that were removed ($175/ton) to make space for the sodium bicarbonate, the net cost of the sodium bicarbonate supplementation is $0.10/cow/day. The gain in milk fat equates to a $0.63/cow/day increase in milk fat revenue and the net return on investment of supplementing sodium bicarbonate would be $0.53/cow/day.

Calcareous Marine Algae

Another option for moderating rumen pH is through feeding calcareous marine algae (CMA). CMA has very strong buffering capacity and often increases rumen pH when fed to dairy cattle (Cruywagen et al., 2015; Neville et al., 2019). The feeding rate for CMA in these studies was approximately 0.20 lb/day. In both experiments, feeding CMA increased rumen pH and reduced time with a low pH more than feeding sodium bicarbonate. It also increased milk fat production by 90 and 270 g in these experiments, which shows that it can have commercial benefits when feeding it to dairy cattle. It is usually more expensive than sodium bicarbonate (~$1400/ton), but it does provide different nutrients in addition to its buffering effects.

Mg Oxide

Mg oxide can aid in modulating rumen pH by acting as an alkalizer. Bach et al. (2018) investigated Mg oxide supplementation to maintain rumen pH when increasing barley, and they observed that providing Mg oxide resulted in greater rumen pH and less time spent with low rumen pH when feeding an additional 3 kg/day of barley. Mg oxide appeared more effective at maintaining rumen pH than sodium bicarbonate in this project. These investigators replicated these results for Mg oxide later on and also observed that Mg oxide supplementation increased NDF digestibility when supplied in diets with the greatest grain inclusion (Bach et al., 2023). In these experiments, Mg oxide was provided at 0.13 and 0.20 lb/day, respectively.

DCAD

Dietary cation-anion difference (DCAD) gets most of its attention for its importance in prefresh rations and controlling hypocalcemia, but DCAD is also critical for increasing milkfat production. Increasing DCAD is also related to feeding ruminal buffers, especially sodium or potassium-based buffers, because they can increase DCAD. So, the effects of some ruminal buffering products may be a result of both buffering ruminal pH and increasing dietary DCAD concentration.

DCAD is usually calculated as follows: DCAD = Na + K – Cl – S. In prefresh cows, we aim for a negative total diet DCAD, but in lactating cows, it must be positive. How positive you ask? Based on the data (Iwaniuk and Erdman, 2015), milk fat yield and concentration continue to increase as DCAD increases up to 500 mEq/kg of diet DM, while DMI and milk yield appear to plateau between 200 and 300 mEq/kg of diet DM. Based on their results, aiming for a lactating dairy cow DCAD ≥300 mEq/kg of DM will increase milk fat production.

How can you increase the DCAD of your ration? Feed more Na and K or feed less Cl and S while still meeting nutrient requirements for each. Some common supplement options are sodium bicarbonate, sodium sesquinate, potassium carbonate, and potassium bicarbonate. Remember, chloride has a negative DCAD so chloride-based salts like sodium or potassium chloride do not increase DCAD like the carbonate versions.

Certain feeds can also have substantial impacts on DCAD. For example, dry distillers grains with solubles (DDGS) has a negative DCAD, which contributes to reductions in milk fat when feeding DDGS in rations that are not properly formulated (Clark et al., 2024). In general, corn-based ingredients like DDGS and corn have lower DCAD than soy-based ingredients like soybean meal and soybean hulls. Formulate the rations accordingly!

Take Homes

Milk fat continues to be a critical part of the dairy producer’s milk check, and we need to use every tool in the toolbox to aid in maximizing milk fat production. Buffers and DCAD considerations when feeding diets can help increase milk fat production. When investigating buffers, you must consider the costs and the benefits. We did the math for sodium bicarbonate as an example, but the same approach can be used for any rumen buffer product. I highly encourage you to base your partial budgets on peer-reviewed literature. Based on the data for rumen buffering and milk fat production, feeding rates of some buffer products are listed below:

• Sodium bicarbonate: 0.4 lb/day
• Calcareous marine algae: 0.2 lb/day
• Mg Oxide: 0.15 lb/day

Also, ensure the DCAD of your ration is >300 mEq/kg to help increase milk fat production.

Properly buffered diets with adequate DCAD will help your herd reach your next milk fat milestone!

References

Bach, A., M. Baudon, G. Elcoso, J. Viejo, and A. Courillon. 2023. Effects on rumen pH and feed intake of a dietary concentrate challenge in cows fed rations containing pH modulators with different neutralizing capacity. J. Dairy Sci. 106(7):4580-4598. 10.3168/jds.2022-22734

Bach, A., I. Guasch, G. Elcoso, J. Duclos, and H. Khelil-Arfa. 2018. Modulation of rumen pH by sodium bicarbonate and a blend of different sources of magnesium oxide in lactating dairy cows submitted to a concentrate challenge. J. Dairy Sci. 101(11):9777-9788. https://doi.org/10.3168/jds.2017-14353

Clark, K. L., K. Park, and C. Lee. 2024. Exploring the cause of reduced production responses to feeding corn dried distillers grains in lactating dairy cows. J. Dairy Sci. 107(9):6717-6731. 10.3168/jds.2023-24356

Cruywagen, C. W., S. Taylor, M. M. Beya, and T. Calitz. 2015. The effect of buffering dairy cow diets with limestone, calcareous marine algae, or sodium bicarbonate on ruminal pH profiles, production responses, and rumen fermentation. J. Dairy Sci. 98(8):5506-5514. https://doi.org/10.3168/jds.2014-8875

Hu, W., and M. R. Murphy. 2005. Statistical evaluation of early- and mid-lactation dairy cow responses to dietary sodium bicarbonate addition. Anim. Feed Sci. Technol. 119(1):43-54. https://doi.org/10.1016/j.anifeedsci.2004.12.005

Iwaniuk, M. E. and R. A. Erdman. 2015. Intake, milk production, ruminal, and feed efficiency responses to dietary cation-anion difference by lactating dairy cows. J. Dairy Sci. 98(12):8973-8985. 10.3168/jds.2015-9949

Neville, E. W., A. G. Fahey, V. P. Gath, B. P. Molloy, S. J. Taylor, and F. J. Mulligan. 2019. The effect of calcareous marine algae, with or without marine magnesium oxide, and sodium bicarbonate on rumen pH and milk production in mid-lactation dairy cows. J. Dairy Sci. 102(9):8027-8039. https://doi.org/10.3168/jds.2019-16244