It is calculated by measuring the total nitrogen content of a forage and multiplying by 6.25. If an animal's performance is limited due to low energy in the diet, excess protein will do little to increase performance. While excess protein can be converted to an energy source by the animal, it is an expensive way to meet energy requirements. Excessive heating after baling can cause some protein to become bound to the indigestible fiber portion. This portion is also included in crude protein.
Available protein is crude protein minus nondegradable portions such as heat damaged protein.
It includes the sum total of the digestible portions of crude protein, crude fiber, nitrogen free extract and fat. It is expressed as a percentage. TDN does not account for any energy losses that occur during digestion. Because of this, TDN values tend to overestimate energy values in forages. NEm refers to net energy for maintenance in beef cattle and NEl refers to net energy for lactation in dairy cattle.