Buffers are compounds that help to counteract an increase in acidity in the rumen. Here we look at dietary buffer supplementation, the points to consider, health and milk production, and we take a look at the impacts on dairy cows.
The cow produces a natural buffer, saliva, which has a pH of around 8.4. She will produce somewhere between 10 and 32 litres of saliva per kg of dry matter consumed, with much higher saliva production when lots of roughage is consumed (Table 1).
What this shows is that a cow fed a diet with only 30% forage naturally produces around 200g less sodium bicarbonate than a cow on the same level of dry matter intake, but with 70% forage in the diet. Because the low forage diet is likely to be more acidic as well, this compounds the problem in that the diet poses more of a challenge and the cow’s natural responses are diminished.
Buffers should not compensate for suboptimal feeding management. Proper feeding management should be considered based on the animal requirements at given production levels. Photo: Mark Pasveer
Buffers are favoured when the following situations exist:
- The forage portion of the diet is low, 45% of DM or less
- Corn silage or other wet, fermented forages are the primary forage sources
- Forages are finely chopped (less than 1.3 cm)
- Dry matter intake is below expectations during early lactation
- Erratic intake or off-feed conditions exist during early lactation
- Hay is limited to 2¼ kg or less per cow daily
- Rations are low in fibre (less than 19% ADF)
- The diet is very wet (less than 50% DM)
- The fat test is abnormally low
- Subclinical acidosis is suspected
- Foot problems such as laminitis, soft soles, or subsolar abscesses exist
Buffers and performance of heifers
In one study, weight gains by the heifers fed the buffered diet were greater. Faeces from the heifers fed the buffered diet had less starch and a higher pH value. The most remarkable result was a 44% decline in feed required per unit gain by the heifers fed the buffered diet (Table 2).
Dietary buffer supplementation in high-producing lactating animals maintains rumen homeostasis by resisting any change in pH. Buffers may prevent an overgrowth of acid-tolerant Lactobacilli, preventing the potential reduction in rumen pH. Although rumen methanogens have been described to be inhibited by a pH ˂ 6.0 in vitro, in vivo CH4- production rates (g/h) did not decrease when rumen pH declined to threshold levels for sub-acute (pH < 5.5) or acute rumen acidosis (pH ˂ 5.2).
The addition of sodium bicarbonate to the cow’s diet can increase the rumen VFA concentrations and alter their molar proportion toward a higher proportion of acetate: propionate ratio. In a study with cows fed 75% concentrate diets, the acetate: propionate ratio increased from 1.31 to 2.0 when supplemented with the buffer. The reason for this change in rumen fermentation is not clear. It may be related to a change in the rumen microbial population or a shift in the metabolism of existing microbes toward more acetate and less propionate production. It may also result from the increased rumen fluid dilution rate due to the increased flow of water into the rumen as an attempt to adjust rumen osmolality. In either case, there is an increase in milk fat percentage since acetate is the main precursor of milk fat synthesis. In other cases, however, milk fat content has not typically correlated with a higher acetate: propionate ratio due to physiological, and genetic factors, i.e. priorities of fat use may be shifted towards tissues rather than milk production.
Milk yield and composition
Dietary buffer supplementation tends to increase DM intake and nutrient digestibility and hence maintains high productivity in lactating animals. Buffers also maintain high milk fat through the mechanisms indicated above. The effect of dietary buffers on milk protein content, however, is not as well defined as the effect on milk fat.
Diets that are acidic (silages) or are high in energy content and produce acidosis, may precipitate the incidence of the displaced abomasum, but with free-choice feeding of sodium bicarbonate, the occurrence of displaced abomasum was nearly eliminated. Also, some references have alluded to the use of sodium bicarbonate in the treatment of ketosis. Feeding corn silage with sodium bicarbonate added before feeding produced lower concentrations of ketone bodies in the blood and urine of lactating cows.
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5 points to consider
1. Limestone (CaCo3) may be used as a buffering agent in place of sodium or potassium bicarbonate. However, it has very low solubility in the rumen and thus plays a minor role in controlling the rumen pH and enhancing animal performance.
2. Magnesium oxide (MgO) may also be considered for this purpose, but it has low palatability and may not thus be consumed in sufficient amounts to enable its biological functions.
3. For reasons that are not fully understood, buffers frequently depress the intake of hay-based diets but increase the intake of silage-based diets. In both cases, however, the other benefits of buffer feeding remain unchanged.
4. The use of sodium or potassium bicarbonate buffers in combination with an ionophore (e.g. monensin, lasalocid, etc.) may nullify the effect of the ionophore on feed efficiency. If buffers are to be supplemented into the diet, it may not be cost-effective to use an ionophore therewith.
5. Buffers should not always be used on a routine basis to compensate for suboptimal feeding management. Proper feeding management should in all cases be considered based on the animal requirements at given production levels.
References are available from the author upon request.