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Replacing summer pasture with feeds for cows grazing pasture

University of Nebraska Extension | Updated: 06/04/2012

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Managing a cow herd in drought conditions is a challenge. An alternative to dry lotting beef cows in drought conditions or when pasture is expensive or in short supply would be to "substitute" some of the pasture with another feed. This concept means that cows remain in the pasture and another feed is fed as a part of the cow's daily feed consumed.

Substituting Feed for Pasture for Cows Grazing Pasture

There has been very little interest to replace pasture with another feed during the spring/summer while cows are grazing pastures, other than supplementing cows with salt and minerals/vitamins. Rightfully so because the nutrient quality of cool- and warm-season pastures, in most cases, are high enough to meet the energy and protein needs of lactating cows. However, if forage production in a pasture is limited due to drought or availability of pasture is limited due to high price or high demand, replacing pasture with feed may be an economical alternative. Producers considering using feed to replace pasture while cows are still grazing the pasture, should follow these guidelines.

They must have the labor and equipment to deliver the feed.
To reduce feeding losses, consider feeding in bunks. However, providing the forage replacement on the ground would allow producers to move the cattle around the pasture to improve grazing utilization of the pasture while reducing erosion due to trampling around a single feeding location.
It must be cost effective and feeds must be relatively cheap compared to total pasture costs.
The feeds used as the substitute for pasture must not have a negative effect on forage digestion because part of the diet is forage from the pasture.

The thought process of replacing pasture with feed for cows grazing pasture would be to replace (substitute) some of the forage/pasture daily intake by the cow with an economical feed that doesn't have a negative effect on forage digestion. If this could be done, stocking rate could be increased on the pasture resource which would spread pasture costs over more cows or the available pasture could be "stretched" and used for a longer period of time. In theory, the rumen has a certain capacity, and once filled, cattle will stop eating. So part of the rumen would be filled with feed other than grass from the pasture they are grazing. This management strategy cannot have a detrimental effect on pasture longevity and sustainability.

Harvested forages such as alfalfa, grass hay, summer annuals could be used in a grazing situation to replace grazed forage and not have a negative impact on the total digestibility of the diet. The challenge using harvested forages to replace pasture is that harvested forages are usually expensive, especially in drought conditions. A second challenge is to get cows to eat the harvest forage instead of vegetative grass in the pasture. Cows likely won't consider eating the harvested forage until grass in the pasture is depleted. If there is daily access to a loafing area that the cattle could be gathered and fed the harvested forage before turning them out to pasture, then consumption of the harvested forage may be possible. This practice would take labor and fuel in addition to the feed and equipment to deliver the feed.

Grains, such as corn, are not a good choice, even if they were cheap as a feed substitute for cows grazing pasture. Data suggest that grains have a negative associative effect on forage digestion. Grains are high in starch and feeds that are high in starch tend to lower the pH of the rumen and make it an acid environment which promotes an increase in microbes that digest grains not forages. The consequence of this is a decrease in forage digestibility.

University of Nebraska researchers have studied supplementing mixtures of wet distillers grains mixed with low quality hay or crop residue in an attempt to replace grazed forage, without removing the cattle from the pasture. Corn distillers byproducts are very palatable and mixing them with low quality forage or crop residues has been shown to increase consumption of low quality roughage and, when fed to cows grazing pasture, will replace pasture consumed. The amount of the pasture replacement has been variable.

One study found that for each pound of the 45:55 ratio of WDGS:grass hay mix consumed by cows the mix replaced 0.22 lb of the grazed forage. This is lower than the targeted goal of 50 percent pasture replacement that was planned. This potentially could have negative impacts on native range health if it were stocked at a rate with cows with an assumed 50% replacement rate. The fiber content of the mix may not have been high enough to provide enough bulk to limit grazed forage intake as desired.

In another study, cow/calf pairs grazed pasture and received either 50:50, 40:60, or 30:70 WDGS:wheat straw supplementation at 50 percent of the estimated dry matter intake. The 30:70 WDGS:wheat straw treatment almost replaced grazed forage on a 1:1 basis. As the amount of WDGS increased in the supplement the amount of replaced grazed forage decreased.

For producers with crop residues in close proximity to their cattle, the 30:70 WDGS:residue combination may be a viable option to reduce grazed forage intake. Studies indicate that a blend of 30:70 WDGS:roughage appears to be the optimum blend to get the most forage replacement. Using this combination of byproduct:forage, producers could plan that for every dry matter pound of the combination fed, between 0.5 to 1.0 pounds of forage in a pasture on a dry matter basis could be replaced.

Source: Dr. Rick Rasby, University of Nebraska

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