Radical nutrient loss on US rangelands marks an “alarming trend”

Cattle grazing in South Dakota.
Cattle grazing in South Dakota. © BLM

Climate change and grazing have led to radical nutrient losses to the forage on America’s rangelands over the past 20 years, it has been revealed.

Researchers have outlined the falling dietary value of forages on unimproved native rangelands in the US over the past two decades, which they have labelled an “alarming trend”.

In the study, Long-term declines in dietary nutritional quality for North American cattle, published in the journal Environmental Research Letters, the researchers suggest that increased prevalence of drought, rising atmospheric carbon dioxide concentrations and sustained nutrient loss from grazing “all have the potential to reduce cattle performance by reducing the nutritional quality of forage”.

The study was undertaken by Dr Jay Angerer, an AgriLife Research rangeland ecologist at the Texas A&M AgriLife Research and Extension Center in Temple, with Dr Joseph Craine, of Jonah Ventures, Manhattan, Kansas, and Dr Andrew Elmore, University of Maryland Center for Environmental Science, Frostburg, Maryland.

They say the “protein debt” is costing producers almost $2 billion annually. The contributing factors have led to cattle “becoming increasingly stressed for protein over the past two decades, likely reducing cattle weight gain.”

The research estimates it costs producers an additional $1.9 billion annually to meet the US cattle herd’s protein needs with supplemental feed.

Angerer said the downward trend in nutritional value on rangelands poses a measurable concern for producers and consumers in the future.

“There are financial implications for producers and eventually the consumer,” he said. “Producers already have enough to worry about, and if their supplemental feed costs go up, their margin shrinks, and that may lead to a decision on whether to stay in the business or get out.”

The Grazing Animal Nutrition Lab at the Temple center collected 36,000 manure samples from cattle in the US that were measured for dietary quality between 1994 and 2015.

Sheep move through public lands near Shoshone, Idaho.
Sheep move through public lands near Shoshone, Idaho. © BLM

The GAN Lab’s short-term goal is to estimate a producer’s forage quality, especially crude protein and total digestible nutrients, using manure samples to help them optimize supplemental feeding regimens, Angerer said. The lab receives and tests samples from all over the US.

Over the years, researchers have dialed in equations and parameters to determine forage quality based on manure samples, the animal, the breed and other factors that help the lab give producers or consultants the information to provide the correct amount and type of supplemental feed throughout the year.

“If producers are looking for optimization, it’s better to look at a number and not a range of numbers,” Angerer said.

Manure samples arrive at the Grazing Animal Nutrition Lab at the Texas A&M AgriLife Research and Extension Center in Temple. The manure samples are analyzed to show producers the nutrient quality of their forages. © Adam Russell/Texas A&M AgriLife Extension Service 
Manure samples arrive at the Grazing Animal Nutrition Lab at the Texas A&M AgriLife Research and Extension Center in Temple. The manure samples are analyzed to show producers the nutrient quality of their forages. © Adam Russell/Texas A&M AgriLife Extension Service

But the long-term look at information provided by the manure samples showed that digestible organic matter and crude protein quality were declining. Over 20 years, available crude protein decreased 1 percent which amounts to an average 10-pound loss per head without supplemental feed.

The US had 86 million cattle that were not on feed, including 27 million calves, in July 2015, according to the study.

Angerer said potential losses depend on the rangeland, the animal’s production stage, growth, lactation, gestation, the season, temperatures and other factors that could increase the amount of supplemental feed to make up for the crude protein losses.

Enriching native grasslands with nitrogen is discussed in the study, but fertilizing millions of acres would be counterproductive, Angerer said, so producers face higher supplemental feed costs or the cost of establishing improved pastures for grazing.

“These aren’t large differences after 20 years, but if that trend continues for 60 years it might get into something that makes a large difference for production capacity,” Angerer said.

The study concluded the protein debt is likely to grow “if the drivers of the reduction of protein in plants cannot be identified and reversed, or adaptation strategies enacted” and could lead to net losses in cattle production.

In 2010, the U.S. Department of Agriculture’s Natural Resources Conservation Service ramped up its conservation stewardship program that provides incentives to producers who participate in the studies.

Angerer said participation in the NRCS program is picking up. Last year, producers turned in 19,000 samples for analysis.

Reporting: Adam Russell

Contributor

This article has been written by a contributor to Horsetalk.co.nz.

Leave a Reply

Your email address will not be published. Required fields are marked *