Beef producers are experts at using a variety of feedstuffs to feed cattle, including crop residue. Racheal Slattery, beef and dairy Extension coordinator, University of Maryland, said there are several reasons beef producers should consider using crop residue in grazing systems.

“The first and most prominent reason is to extend the grazing season,” said Slattery. “For most people who do spring calving, grazing residue is an excellent maintenance diet.”

Grazing crop residue can also aid in keeping cattle off grass pastures during wet and muddy winter conditions, similar to designating a sacrifice pasture.

The primary crop residues available for grazing include corn, soybeans and sorghum. Slattery explained several key terms that ensure animal nutritional requirements are met.

“Crude protein (CP) is the amount of nitrogen in feedstuffs,” said Slattery. “It’s a measurement of protein. The other factor is total digestible nutrients (TDN), which is the total amount of digestible fiber, protein, fats and carbohydrates in the feedstuff. TDN is used in forages to determine nutrient content and available energy.”

It’s important to know the nutrient profile of a forage prior to using it as feed. This information is available from Cooperative Extension and feed consultants.

Cattle typically graze crop residue by first consuming any grain on the ground. Next, they’ll eat the husks or leafy portions. Last to be consumed are the less desirable cobs, stalks or stems.

“When they start eating, the TDN, or nutrient level, is around 70%,” said Slattery. “As the season goes on and they eat stalks and leaves, the TDN drops to about 45%. The average TDN is about 55% and about 5.5% CP, which is reasonable for a maintenance diet.”

Prior to grazing residue, it’s important to determine the stocking rate – how many animals can be put on a given field. “It depends on the bushel yield,” said Slattery. “It’s important to know what the bushel yield was, or if you’re renting ground (to graze after harvest), how many bushels came from the field.”

The basis for determining how many days animals can graze crop residue is a 1,200-lb. dry cow on a maintenance diet. “Start with the amount of corn in bushels – 180 bushels is standard,” said Slattery. “Divide that number by 3.5 and the (answer) 51 gives us grazing days per acre.”

Even in the best conditions, cattle grazing harvested fields only use about 50% of what’s available due to trampling, weather and degradation over time. Other factors that influence usage include the number of animals grazing, the average weight of animals, days of grazing and grazing acreage.

“There are some outside factors that affect stocking rate,” said Slattery. “The big one is weather. Snow over five inches deep is going to slow them down and discourage them from digging through. More important is ice because it can hold down the forage so animals can’t get to it.”

Another factor is how the area will be grazed – whole field access or strip grazing. “Whole field has benefits,” said Slattery. “Cows go through and pick all the good stuff first, but there’s more trampling and loss. Strip grazing allows for more uniform intake of nutrients and greater gains, if the weather cooperates.”

Overall field yield and harvest practices also affect stocking rates. This depends on combine efficiency and the number of dropped ears and broken stalks.

Since crop residue is primarily for maintenance, it’s important to determine whether supplemental feed is needed. “When feeding crop residue, the goal is to maintain animals where they are,” said Slattery. “It isn’t to get gains. Feeding crop residue is to maintain body condition and weight.”

Slattery said the perfect candidates for crop residue feeding are spring-calving dry cows in good condition. These animals typically don’t require supplemental feeding unless weather conditions make it difficult for them to access crop residue. Spring-calving cows that are thin (BCS under 4.5) will require supplemental feed to provide sufficient protein and energy to build body condition and maintain pregnancy. A starting point for this group is 1 lb./head/day.

“Spring-calving first calf heifers need more energy and protein, and need at least three pounds per head per day,” said Slattery. “Fall-calving cows are the highest maintenance group. They’re dropping weight with lactation and are going to be bred back. The goal is to put condition on them and maintain it. This is harder to do on corn stalks, so feed at least 4.5 to five pounds per head per day, depending on calf size.”

It’s important to remember that calves at two to three months old start to graze with their dams, so make sure there’s sufficient grain for both cows and their calves. Supplementation rates are only starting points – keep a close eye on the herd to ensure animals are gaining or maintaining condition.

While crop residue grazing is a good economic option for many beef producers, there are some challenges. Many corn, soybean and sorghum fields don’t have perimeter fencing, so grazing such fields involves installing temporary perimeter fence. Producers should determine whether the expense of fencing will negate any gain from grazing crop residue.

Crop fields typically don’t have water sources, so producers should determine whether it’s practical to supply water to the field.

“A big consideration is prussic acid in sorghum,” said Slattery. “Sorghum is a great forage until there’s a hard freeze, which causes a buildup of prussic acid and is deadly to cattle.”

Slattery added that the Mid-Atlantic region commonly experiences hard freezes followed by warmer weather and new plant growth. The new growth, suckers, are highly toxic. Animals should be kept out of a sorghum field for two weeks following a hard freeze to allow prussic acid levels to drop.

Another negative is that cattle are prone to grain overload, which can lead to acidosis and/or founder. “This can happen if there are a lot of dropped ears, or if the combine dumped grain on the ground,” said Slattery. “This happens more in older, experienced cows that have learned to pick out ears and clean them quickly.”

To avoid grain overload, scout fields for grain piles and excess dropped ears, and if possible, strip graze that section to limit cows’ exposure to grain. Alternatively, younger animals can graze such areas prior to putting mature cows out to graze.

Ideally, cattle should be fed dry hay first to fill them up, then allowed to graze crop residue. This pattern of alternating dry hay and grazing can help avoid excess grain consumption in a short time.

Slattery referenced a University of Nebraska calculator that provides more specific information about CP and TDN as well as other considerations such as transportation expenses and the cost of care and supervision of animals as they graze crop residue. This tool can help graziers determine whether grazing crop residue is cost-effective.

To use the UN corn stalk grazing calculator, visit beef.unl.edu/learning/cornstalkgrazingcalc.shtml.

by Sally Colby