cows in field


Weeds or Forbs?

Jeff Semler

By Jeffrey Semler, Extension Educator, University of Maryland Extension-Washington County, a part of the College of Agriculture and Natural Resources (AGNR), University of Maryland

We are pleased to announce that Jeff Semler will be an active educator at the 18th Annual NODPA Field Days in Knoxville, Maryland on September 27 & 28, 2018. In addition to co-facilitating the session Maximizing Net Income for the Future of your Farm: Learning how to do more with less, he will also be attending both of the farm tours and sharing his grazing expertise.

It is often said the beauty is in the eye of the beholder and nowhere is this truer than in the pasture. By definition, a weed is an unwanted plant or a plant out of place. To many livestock producers, a weed is any plant other than grass.

Jeff Semler

Weeds constantly invade crop fields and pastures; therefore, it is important to know the potential quality of individual weed species in making management decisions concerning weed control. Some weeds are toxic or poisonous to livestock, and certain weeds are unpalatable – causing a reduction in total intake. Several weed species have thorns or spines that can injure the grazing animal’s mouth and/or irritate its eyes, which may lead to pinkeye. Other weeds can cause the milk and meat of livestock to have a negative taste or odor.

In addition it is often assumed that weeds have low nutritive value and livestock will not eat them, so expensive and time-consuming measures are often used for their control. However, many times this is not true and these weeds should be more rightly called forbs.

So what are forbs? They are broad-leaved, non-woody, herbaceous plants that differ from grasses in that the latter have narrow, linear leaves. Many forbs have significant food value for livestock and livestock even prefer them to grasses. Many of these forbs have high digestibility at the vegetative stage that is even higher than some cultivated forages.

For more than a decade the University of Maryland Extension Small Ruminant Team ran the Western Maryland Pasture-Based Meat Goat Performance Test located at the Western Maryland Research and Education Center (WMREC). In addition to evaluating the postweaning performance of male goats consuming a pasture-based diet, we look at different forages as well including forbs.

Lambs Quarter Seelding

Over the years we have tested many of the more common pasture “weeds” that include marestail, lambs quarter and burdock as well as planted forbs like Sunn Hemp. We have taken samples for forage analysis shown in Table 1.

Species Dry Matter Crude Protein TDN RFV
Mixed Grasses & Forbs 30% 14.1% 65.8 111
Lambs quarter 28% 23.2% 89.6 289
Marestail 19.8% 19.2% 71.6 174
Sunn Hemp 16.8% 20.0% 75.8 278
Millet/Sunn Hemp 15.2% 21.8% 72.6 174
Orchardgrass 43.9% 9.9% 53.5 73
Alfalfa 26% 25.1% 70.2 234

RFV is an index used to compare the quality of forages relative to the feed value of full bloom alfalfa. RFV is used to compare similar forages for two important qualities—how well it will be consumed and how well it will be digested. Crude protein (CP) is essential in all livestock diets, but the required amount is dependent upon livestock type and stage of life. Most weeds and forages satisfy the CP needs of beef cattle, goats, and sheep.

Yet the quality of a weed or forage has no value if the animal will not eat it. Cattle tend to eat mostly grasses in a pasture, leaving herbaceous weeds and shrubs untouched. Sheep graze broadleaf plants before grasses and shrubs, while goats will eat the shrubs not grazed by sheep or cattle. Therefore, combining cattle, sheep, and goats in a pasture can lead to increased utilization and profitability.

Cow Enjoying Some Forbs

While weeds are an inevitable component of pastures and hay fields. The above table shows that herbaceous weeds can have digestibility that is greater than or equal to high-quality species like alfalfa. Producers should be knowledgeable about the nutritive value of weeds and forages so they can make the best management decisions for their particular operation.

Jeff Semler, Extension Educator, AGNR, UME – Washington County, 7303 Sharpsburg Pike, Boonsboro, MD 21713. He can be reached at:, or by phone: 301-791-1304

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