Ruminants are able to eat and make use of food materials that simple-stomached animals, like people, can’t. This is because the rumen acts a large fermentation vat, where the various microbes (bacteria, protozoa and fungi) digest plant material. Energy in their diet as carbohydrates, both starch and cellulose, are converted to volatile fatty acids (VFA – acetic, propionic and butyric acids), which are absorbed mainly across the rumen wall. Ruminants then use the VFA themselves to meet their energy needs. For a dairy cow, approximately 70% of her energy is provided by VFA and approximately 70% of VFA produced in the rumen is absorbed across the rumen wall.
At calving, a dairy cow’s energy requirement approximately doubles and we want to supply as much of that energy as possible in the diet. The more energy that is supplied in the feed, the less needs to come from fat and muscle breakdown. However, most importantly, we need to maintain a healthy rumen; the key indicator of that is rumen pH. A healthy rumen pH is 6.0; if the rumen pH drops below 5.8 for significant periods of time, there are adverse effects on both the rumen microbes and the cells lining the rumen. Therefore, although we want to supply as much feed energy as we can to the cow after calving, we don’t want high levels of VFA to reduce the pH too much.
The hurdle to overcome is how quickly these VFA can be absorbed. The rate of absorption is largely determined by the surface area of the lining of the rumen, which is made up of papillae (finger-like extensions of the inner wall). These papillae expand when there is a demand for increased VFA absorption, ie when there is a change from a dry cow to a milking cow ration (see photos below), but this process, called rumen adaptation, takes up to 6 weeks.
Therefore, there is an inevitable drop in rumen pH after calving, as the rumen takes time to adapt to the new ration the cow is being fed. This is why concentrate feeding is gradually increased after calving. If the rumen pH drop is too great, then rumen health, and hence cow health, will be affected. Glycal Forte® is very effective in minimising the extent of this pH dip after calving and hence minimising the effect on cow health.