Emergency help for an overloaded rumen
To prevent the occurrence of rumen acidosis, it’s important that the feed ration is uniformly mixed, which can be ensured through sufficient mixing time, and the addition of water if needed. Sudden changes in feed should also be avoided, and the ration must be balanced to ensure a high starch level is offset by a sufficiently high level of digestible cell walls/NDF and a CAB value of between 200-300 meq/kg dry matter.
A cow produces bicarbonate itself in its saliva, which helps stabilise rumen pH, as it’s basic. But the amount a cow can produce itself is not always enough to protect an overloaded rumen from rumen acidosis.
If the ration is composed to avoid overloading the rumen, e.g. with a high level of starch, low level of cell walls or a low CAB value, it can be compensated to some degree by adding a buffer, which will usually be in the form of sodium carbonate. Sodium carbonate has a high CAB value of 11.739 meq/kg. Another way of helping a troubled rumen is by adding live yeast cells, which actively ensure a better composition of rumen microorganisms, in which the number of cellulolytic (fibre-decomposing) bacteria and the lactic acid-consuming bacteria are increased.
Marden et al. 2008 described the effect of adding 150 grams of sodium bicarbonate or 5 grams of live yeast cells to a ration of pH in the rumen, compared with cows in a control group on the same basic ration, but with none of the problem-solvers added. They found that the cows receiving added sodium carbonate had the highest rumen pH of an average of 6.21, followed by the group given live yeast cells, with an average rumen pH of 6.14, compared to the control group value of 5.94. Cows given live yeast cells had a lower level of lactic acid in the rumen, and higher fibre digestion, where the sodium bicarbonate acted mostly as a chemical buffer that boosted rumen pH. Figure 1 shows the results from the trial on the effect on rumen pH.
To achieve the best effect from the addition of sodium bicarbonate, it should be added directly to the feed ration, perhaps through the minerals or feed concentrate, as the cows cannot adjust their intake of sodium carbonate to suit their needs themselves. Keunen et al., 2003 have described this based on a trial in which cows contracting rumen acidosis by increasing the amount of starch in their ration through higher amounts of feed concentrates at the expense of high-structure roughage, did not increase their intake of sodium bicarbonate when it was provided alongside their ration.
The cow can therefore not adjust the need for buffers itself, and the practice used on a number of farms under which the cows are given unrestricted access to sodium bicarbonate in bails, e.g. at each end of the feeding trough, is not the best, as the cows are unable to determine their intake according to their need. The trial also indicated that there were significant differences in the amount of sodium bicarbonate intake for individual cows.