Bacteria in the rumen have a minimum protein requirement to be able to digest fiber efficiently.
The normal minimum is around 8% for this bacteria to be able to be efficient. The consequences of not meeting this minimum will vary depending on the environment and the amount of fiber in the forage.
With low content of lignin in the forage the cow will be able to overeat up to 40% above her dry matter requirements to be able to make up for the deficiency, thus decreasing the amount of cattle carried on a given area of ground.
This is very important under conditions of forage shortages or when land is expensive and we want to optimize number of cows per ranch.
Number of cows per ranch is the most important factor determining profits per ranch. It is far more important than calf-crop percentage or weaning weights. Normally, beef producers don’t realize this and that's why some of them recommend never supplementing to keep expenses down but in reality they are shorting their income due to inefficiency of their cows under forage shortages due to a protein shortage.
With high lignin in the forage the cow is not able to overeat because the high lignin, not being well digested by the microorganisms due to a lack of protein, plugs the digestive system, so to speak. That decreases the forage intake, leading to lower performance. This is the reason cows on low-octane tropical grasses lose weight. Remember when I talk about low-octane tropical grasses I'm referring to forages such as Bermudagrass and Bahia grass.
In this case, if we supplement enough protein to put around 8% protein in the total daily intake, the cow will be able to increase her forage intake to around 2.5% of her body weight and be able to nurse her calf through the winter or drought without losing weight.
This is much easier and cheaper than feeding hay, with savings around $100 per cow per year.
With stockpiled forage the mineral program becomes very important as any deficiency in mineral or protein will increase the amount of dry matter required and with high-lignin forages the animal will not be able to overeat enough to make up for the deficiency.
There is a definite big difference in the grazing management and supplementation under high quality forages in good environments compared to low quality forages in difficult environments.
Similar things happen with animal genetics. The things that makes a breed or animal type excel under a particular environment will make it un-adapted to an opposite environment.