The linkages between the glucose molecules in cellulose How then do cattle get enough nutrients from eating grass?

The fermentation process in the rumen is the main reason why cellulose is able to be broken down enough so that cattle can get their energy (in the form of glucose, as well as protein and carbohydrates) from grass. The fermentation process in the rumen, water absorption in the omasum, and redigestion (for proteins and amino acids) in the abomasum, enable cattle to get nutrients from grass and not starve off of it like humans would (who are monogastrics, animals with one simple stomach that is designed to break down proteins and carbohydrates, not plant matter).

Nutrient content also depends on the stage of life the grass is in. Less nutrients tend to be found in grasses that have new growth (or less than 12 inches in height), and are brown and dead (or have reached maturity and gone into dormancy). The most nutrients can be found in grass that is in the vegetative stage, which is best between when the average height is 10 to 12 inches and when the inflourescences (flowering head) have just started to emerge. Nutrient quality decreases incremently when the grass has its flowering head fully emerges, exposes its reproductive structures (i.e. anthers), and goes to seed. Nutrient quality declines at these stages because 95% of the plant's energy is put into producing seed, and only 5% into leaf growth.

Thus knowing the stages of your grasses in your pasture can best determine the quality of th grass and what your cattle are getting from the pasture in terms of weight gain and eating habits.