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Animal Health

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Nutritional Additives

Sodium bicarbonate: a mineral-based solution for cattle during heat stress


Dr. S. Mouzon, J. Perez, Products and Applications Development, NOVACAP



With warmer weather and increase of temperature, dairy cows – especially high yield cows – are starting to suffer. As soon as temperatures reach 20°C and in the event of high humidity, they remain standing, seek out shade, drink more water, refuse food, etc. And these are only the external signs. Usually these changes in behaviour are connected with a drop in production, reduced fertility, and an increase in metabolic disorders. The cows are suffering from heat stress. Although measures can be taken to limit the impact of intense heat, there are also dietary and nutritional solutions to overcome the physiological reactions and limit the consequences on production performance.

In such a situation, sodium bicarbonate is a particularly effective ally.


What effects does heat stress have on the cows?

Cows try to adapt to the temperature increase.
For lactating cows, this situation of heat stress can lead to a risk of acidosis. Respiratory rate of lactating cows increases to evacuate the heat. This causes more CO2 to be eliminated, which leads to a compensatory consumption of plasma bicarbonate. Bicarbonate is less readily available to act as a buffer substance in the rumen. Food consumption drops to minimise digestion-related temperature increases. The consumption of concentrates remains almost the same, but a lower intake of forage means less rumination and saliva production and, as a result, less sodium bicarbonate released in the rumen. The drop in food consumption will be made up for after the heat stress. Intake will increase, but the rumen will not be ready. These points highlight how heat stress can be a source of ruminal acidosis if no nutritional changes are made. Furthermore, perspiration increases to eliminate as much internal heat as possible. This provokes a loss of minerals such as sodium and potassium.

For pregnant and dry cows, the situation of heat stress can lead to reproduction problems: curtailed gestation, increased risk of non-delivery, harder beginning of lactation-due to lack of energy, increased risk of illness in calves.


When does a cow suffer a heat stress situation?
Temperature Humidity Index (THI) is a measure that has been used since the early 1990s (Figure 1). It accounts for the combined effects of environmental temperature and relative humidity, and is a useful and easy way to assess the risk of heat stress. The threshold value of the index is 68.
  • When the THI exceeds 72, cows are likely to begin experiencing heat stress
  • When the THI exceeds 78, cows milk production is seriously affected
  • When the THI rises above 82, very significant losses in milk production are likely, cows show signs of severe stress and may ultimately die.
Figure 1. Critical values of THI depending air temperature (°C) and relative humidity (%)
For example, a THI of 72 occurs at:
  • 26°C and 40 % relative humidity
  • or 23°C and 80% relative humidity.
Prevention methods
Several methods exist to limit the effects of heat stress.
First the farmers can modify the diet by distributing fresh and high quality rations with a change in the energy density: digestible cellulose, slow starch, and by adding water to the ration to achieve a dry matter rate of 45% to 50%. It is also recommended to split the feed distribution to limit digestion-related heat release, and to distribute the feed during the coolest hours.

As heat stress provokes a loss of minerals, it is mandatory to increase the concentration of minerals, in particular sodium and potassium. For the feed ration, the farmers must aim for a DCAB (Dietary Cation-Anion Balance) of 350 to 400 meq/kg dry matter by reducing the salt content and increasing the share of sodium bicarbonate. Sodium bicarbonate is not only a sodium supply but it is also highly efficient to regulate the pH in the rumen thus preventing from acidosis.


Benefits of Sodium Bicarbonate


To demonstrate the efficiency of sodium bicarbonate, Novabay has carried out an on-field zootechnical test on a herd of dairy cows. It has enabled to evaluate the effect of sodium bicarbonate on feed consumption, milk production and ruminal pH in standard conditions and in case of heat stress.
The trial took place in Europe. About 500 cows were in lactation in the farm where the average milk production is about 12000 kg/ dairy cow/year.

The cows were separated in homogeneous groups according to their milk production (high production or medium production) and their lactation number. 325 dairy cows, of parity range from 1 to 3, were assigned to the experimental treatments. The characteristics of each group were the following ones (Table 1):



Table 1:  characteristics of the experimental groups
The group P6 was only constituted of first-calving cows. The groups assigned in the feeding group 1 were P5 and P4 and in the feeding group 2: P3 and P6. The dairy cows were fed with the experimental diet, during 16 weeks with 2 periods of 7-9 weeks. The cows were bedded on sand-litter.
During the trial, the two feeding groups received the basal diet (Table 2) described below and completed with complementary feed containing sodium bicarbonate at the level of 1% of total dry matter.
Sodium plays a positive role in the DCAB (Dietary Cation-Anion Balance) equation:
DCAB = ([sodium] + [potassium]) - ([chlorine] + [sulphur])

Sodium bicarbonate is a chlorine-free source of sodium, which makes up for losses without penalising DCAB. The recommendations for use are 250 - 400 g/cow/day (up to 400g during the heat stress and for the following 10 days) in the form of sodium bicarbonate.


The TMR (total mixed ration) was distributed twice a day and brought closer six times a day. Distributed quantities were measured by the Unifeed distribution system. Quantities of uneaten feed were weighed and removed before each new distribution. The ration was revised each day according to the quantities of feed distributed and of uneaten feed. The quantities were revised and registered twice a day.


Table 2:  basal diet composition (kg)


The production performances were expressed as:

  • Daily feed intake per group expressed in quantity of dry matter
  • Weekly Milk production per group
  • Feed conversion ratio per group (calculated)
  • Continuous measurement of rumen pH for 4 cows (2 in P5 group; 2 in P6 group) with the electronic e-Cow® bolus. The measures were collected every 2 weeks.

During the 2 phases, the feed consumption (Dry Matter Intake) has been measured for the two feeding groups (Table 3).


Table 3:  Dry Matter Intake per group and phase


Feed consumption was higher in the 1st phase versus 2nd phase. The consumption was higher in group P5, which is related to the higher level of production, requiring more quantity of feed.
During the 2nd phase, all the groups presented a lower feed consumption, because of heat-stress (THI 78), and there was no difference between the groups P5, P4 and P3. Like in the first step of the trial, the group P6 still consumed less feed than other groups which must be attributed to the first-calving status.

The data presenting the milk production for each group (Table 4) confirmed the differences in performances between the high level and mid-levels of production cows and between 1st and 2nd phases



Table 4:  milk production per group and phase

Because of a severe heat stress, milk production decreases for the 4 groups from -2 to -5%.
But what really matters is the capacity of each group to transform feed into milk (called "feed efficiency FE"). According to Table 5, there are differences among the 4 groups. Even if P3 and P4 have a similar ingestion rate, it can be seen a better transformation rate for P3 than for P4 in the 1st phase. Unexpectedly, due to their first-calving status (it is supposed that these cows use a part of the feed energy for their growth) the P6 group presents a feed efficiency better than groups P3 and P4.

In the 2nd phase, all the groups have increased their capacity from 0.6 to 6 % by a diminution in feed intake (due to heat-stress) more important than the reduction in milk production.



Table 5:  feed efficiency per group and phase

During heat-stress, sodium and bicarbonate ions (HCO3-) amounts decrease because salivation lowers and perspiration increases. Sodium bicarbonate supplies these two components and allows to compensate these lacks. The increase of feed efficiency is also linked to the regulation of pH due to the ingestion of sodium bicarbonate.
During the test, the pH was recorded by electronic bolus and limit values of 5.8 (reference limit from e-cow) and 6.0 have been chosen to evaluate acidosis risk respectively of the high productive cows from P5 and of the cows of P6 groups.

Looking at daily pH measurements (Figure 2), the variations followed the same trends whatever the group, corresponding to the period of feed ingestion:

  • from 10:00 pm to 8:00 am : increase
  • from 8:00 am to 2:00 pm : decrease (following the first feed intake)
  • from 2:00 pm to 5:00 pm : increase
  • from 5:00 pm to 10:00 pm : decrease (following the second feed intake)
Figure 2:  Daily rumen pH variations


Figure 3 (a & b) corresponds to the pH values during the whole 1st phase (no heat stress).


Figure 3.a : 1st phase pH of group P5 cows


Figure 3.b : 1st phase pH of group P6 cows
In the 1st phase, high producing P5 cows are 1.16 to 1.65 days at ruminal pH below 5,8. The ruminal pH is lower for this group due to higher feed intake (almost +10% compared to the group P6).
In the group P6, the mean value for ruminal pH is always over the value of 6 during the whole 1st phase of the trial.

Figure 4 (a & b) corresponds to the pH values during the whole 2nd phase (heat stress).


Figure 4.a : 2nd phase pH of group P5 cows


Figure 4.b : 2nd phase pH of group P6 cows
During the whole 2nd phase, a decrease of the pH was observed whatever the group, linked to heat stress which induces a lower release of sodium bicarbonate from the saliva in the rumen. In normal THI (< 68), sodium bicarbonate produced by saliva enables to neutralize the acidity of 14 kg per day feed intake in average. The P5 group cows displayed ruminal pH in quasi permanence below 5.8 (and in permanence below 6). By contrast, in the cows of the P6 group the ruminal pH is never under 5.8 (only 1.5 d on 28 days below 6 for 1 of the 2 cows). However the pH decrease is limited to 5% due to the sodium bicarbonate complement in the ration.

Providing sodium bicarbonate through nutrition offers the rumen a buffer to limit the risk of acidosis.


However once the heat stress is over, the risk of acidosis persists because the animals eat more to make up for the drop in ingestion brought about by the heat stress. Buffer substances must therefore be distributed past the hot period.




During heat-stress (and for the following 10 days), the use of sodium bicarbonate is recommended between 250g and 400g/cow/day. Sodium bicarbonate has several benefits:

  • Sodium supply
  • Bicarbonate ions supply
  • Positive effect on the Dietary Cation Anion Balance (DCAB)
  • Prevention of rumen imbalance thanks to its buffer property, particularly during feed transition periods

Consequently, sodium bicarbonate allows to:

  • prevent disorders linked to chronical acidosis: loss of appetite, foot problems, fall in milk fat, susceptibility to mastitis, fertility issues
  • maintain an optimal level of milk productivity.



NOVACAP - Mineral Specialties Division is a French producer of sodium bicarbonate, a mineral compound manufactured from natural raw materials. Since 1855, our key values are Responsiveness, Quality and Reliability to gain your satisfaction. We offer a wide range of sodium bicarbonate grades suitable for use in high-end applications for various markets: pharmaceutical, personal and home care, food and feed, environment. In 2017, NOVABAY - our new facility located in Singapore - opens, with a 70kt production capacity. In Asia, NOVABAY is your natural partner with state-of-the art technical support to propose you a solution meeting your needs in terms of performance and innovation. The passion for quality and the satisfaction of our customer's needs are our main goals. NOVABAY stands out not only by the high level of quality of its products but also by its culture of excellence, offering its clients the best service, thanks to the reactive approach and reliability of its team. We ensure quality and safety management with a high level of compliance and certification, application of rigorous procedures and controlled processes and equipment adapted to the needs of our customers.



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Article made possible through the contribution of Dr. S. Mouzon, J. Perez, NOVACAP

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