"Normally, feeding supplemental protein is necessary and justifiable when the available diet does not meet an animal’s nutritional requirements," says Ed Huston, an emeritus beef cattle nutrition professor from Texas A&M University.

That typically occurs when grass pastures become dry and dormant, and protein content in the plants drops off. Protein supplements also can be important with winter grazing. Dormant winter range forage is usually very low in protein, making a protein supplement beneficial, according to Houston.

The periods of calving through breeding are also critical nutritional periods for cows, "but if you are feeding a good-quality hay during that time, the protein content may be enough that another supplement isn't needed," he adds.

As a rule, high-producing cows need up to 3 lbs. of crude protein/day during lactation. Huston says a common mistake producers make is providing supplement when cows don't need it.

"Often, personal preference leads producers to feed more supplement than is necessary for economic return,”" Huston says. "Much of it hinges on how a producer reacts to seeing a fat cow vs. a thin cow."

To know when protein supplements are necessary, Huston says, takes a critical eye.In a cow-calf operation, watch the cow's condition. A body-condition score (BCS) of 4 to 6.5 is a good target. If her BCS gets above or below that, something needs to be done.

Another tip, consider sorting. "The better you can sort animals into uniform feeding groups to better target their needs, the better off you are," says Huston. For example, he suggests sorting thin or younger cows from older boss cows. "When fed in one large group, intake can be variable. Often, those who need nutrients the most get the least due to the bully factor," he adds.

And, evaluate different protein types. Huston suggests utilizing a natural protein when possible. "Urea or non-protein nitrogen is only about 75-90% as effective as natural proteins. So unless there is a real cost savings, use natural protein based on a price vs. protein content ratio," he says.