Gil, Enrique. Feeding Value of Forages. Library. College of Agricultural Sciences (UNMP). Balcarce. Argentina. 1994.

Summary
We can summarise some of the conclusions of this research indicating that pastures of the temperate regions are an excellent food source to sustain cattle production under grazing conditions, due to their high digestibility levels. This permits high feed intake that has as an outcome optimal animal production.
Nevertheless, there are periods when the pastures have different growth stages, and at different times of the year the nutritive value of the forage decreases due to the low efficiency in the use of nutrients by part of the animal. The main factor to consider and that determines this low efficiency is the unbalance in the energy:protein contents of the forages. As the temperate zone pastures are the main component of the animal's diet in our production system and considering that there is an unbalance during certain periods of the year, the feeds given to these animals to compensate this unbalance should be considered more from their point of view of their nutritional balancing action than that of their influence as a nutritional feed supplement. Feeds such as cereal grains, balanced rations and concentrates in general, as also silage and hays should be taken into account in the animal's diet, not only as an addition of needed nutrients, but also from a point of view of covering the nutritional deficiencies of the pastures. This important concept would tend to change the classification that we have today of the different feeds.
Besides the concept of "forage balancing" for pastures, there are certain chemical/physical forage treatments that have experimentally shown their effectiveness in the control of nutrient losses at ruminal level. Treatments with formaldehyde or temperature permit a decrease in the degradability of proteins in the rumen, although this system is not always practical and easily applicable by the producer. Also the use of certain additives that control ruminal fermentation such as tannins, ionosphores such as monensine, starches, substances that capture ions in the rumen such as zeolite or glucocomponents extracted from the yucca plant, etc., could be considered and are today been evaluated and do have a promising effect on the improvement of the nutritive value of grasses, by bettering ruminal fermentation.
There is no doubt that this area of research presents important possibilities and the greater challenge is in the phytogenetic improvement of forage species. Today we can count with tools that through biotechnology and genetic engineering permit us to visualise changes in the composition of forages that a few years ago would have seemed an impossibility.

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