The effects of drought on a grazing system are like a chain reaction. First, dry weather hinders plant growth and resiliency, which reduces forage yield and quality. Then, livestock intake is limited and animals can’t meet their nutrient needs.

An added concern arises when lactating cattle are included in this negative feedback loop. These animals have greater protein and energy requirements, especially late-spring calving cows that must be bred in the heat of the summer.

“When rainfall is adequate and proper stocking density is used, the grass in July and August is typically adequate to support the needs of the lactating and cycling cow,” says Karla Wilke with University of Nebraska-Lincoln. “However, in a severe drought, not only is there risk of overgrazing and damaging pastures, there is also a risk of having a high percentage of open cows.”

The extension cow-calf systems and stocker management specialist suggests that supplementing cattle on pasture with wet distillers grains and crop residue can improve their nutrient intake and extend grazing, but it must be done correctly. For example, if only a small amount of wet distillers grains is provided to animals, they may actually consume more forage and exacerbate overgrazing.

On the other hand, supplementing cattle with enough wet distillers grains to equal 0.6% of their body weight on a dry matter basis has been shown to replace 10% to 12% of the forage in their diet. Furthermore, mixing wet distillers grains and roughage can have even better results.

“When wet distillers grains and ground wheat straw were mixed at a ratio of 30:70, respectively, the forage replacement value was almost 1:1,” Wilke notes.

Wilke continues to explain when wet distillers grains to ground wheat straw were fed at a ratio of 50:50, or when hay was fed in the mix instead of crop residue, the forage replacement value was only about 44%. Therefore, this strategy can stretch pasture supplies to some extent, but if forage replacement value isn’t 100%, overgrazing can still occur.

Feeding and weaning

Some cattle confinements may not be equipped with feedbunks or water tanks designed for calves, so it’s sometimes necessary to take supplemental ingredients to livestock in the field. Use pasture bunks that can be accessed from both sides, or feed cattle on the ground.

Early weaning is another solution to alleviate grazing pressure on drought-stressed pastures, but Wilke notes doing so before calves are 90 days old can be labor intensive. Buyers might also be less inclined to purchase younger calves.

“An April-born calf is only 60 days old in July. Therefore, for some producers, feeding pairs on the pasture may be the best option until the calf is 90 to 120 days of age,” Wilke states. “This also reduces the risk of pathogen loads for the young calf and gives them an opportunity to graze some forage as well.”

In summary, supplementing livestock during a drought can substitute forage in their diets and benefit the grazing system. Feeding wet distillers grains and crop residues can also help lactating cows meet target protein and energy levels. This approach can be combined with early weaning, but there are some consequences to consider.

Amber Friedrichsen
Amber Friedrichsen is the 2022 Hay & Forage Grower editorial intern. She currently attends Iowa State University where she is majoring in agriculture and life sciences education-communications and agronomy. Friedrichsen grew up on her family’s diversified crop and livestock farm near Clinton, Iowa.