WESTERN PRODUCER — In the cattle industry, a 14 per cent difference in weight gain is substantial. It’s the difference between a 600 pound and a 700 lb. steer.
The 14 per cent, in this case, comes from U.S. Department of Agriculture research that compared continuous grazing and rotational grazing.
The scientists behind the research, which was conducted at the Central Plains Experimental Range in northern Colorado, determined that cattle gained 14 percent less weight in rotational grazing because they consumed lower quality forage.
“Cattle did not have as much freedom to roam and be more selective on what to eat, so they ended up eating what was available in front of them, which was lower quality forages with less protein,” said David Augustine, a research ecologist with the USDA in Fort Collins, Colo.
“These behaviours were directly correlated to the average of 14 percent reduction in steer weight gain in the multi-paddock rotating system, compared to the non-rotational continuous system.”
Rotational grazing involves dividing pasture into paddocks. The cattle herd is kept in one paddock for a short time, possibly several days, before being moved to the next paddock.
“The concept behind rotational grazing is to harvest the grass quickly and then give the forage time to recover and regrow,” says the Ontario agriculture ministry website.
Under rotational grazing, cattle will eat the less desirable plants, increasing stocking rate and production per acre.
More than a decade ago, Augustine and a group of USDA scientists decided to look at rotational grazing and the scientific evidence that it’s more sustainable.
Advocates of rotational grazing say it produces more pounds of beef per acre, increases forage productivity, improves forage quality and makes pastures more resilient to drought.
There’s been dozens of experiments and research on rotational grazing, but few have been done at a scale that’s comparable to the real world, Augustine said.
The USDA research is unique because of its size and the 10 year timeline for the study, which began in 2014.
“This was a designed experiment, where we intentionally set up paired pastures,” Augustine said, noting that ranchers, scientists, conservation groups and government reps worked together to design the experiment.
The paired pastures were 320 acres in size. One 320-acre pasture had rotational grazing and the other had continuous grazing. They repeated the pairing 10 times.
The number of animals in each pasture was identical in both treatments. It ranged from 214 to 280 steers per year for the half section of pasture.
“We wanted to keep stocking rate constant,” Augustine said.
“The only difference is the movement of the animals in space and time.”
The density of cattle in an individual paddock for rotational grazing was 10 times higher than the density in the continuous pasture.
After the first five years of the study, the USDA scientists found that steers in the rotational pastures gained 14 percent less weight because they were consuming lower quality forage.
“A fundamental tenet of adaptive, multi-paddock grazing is that long rest periods are vital for the enhancement of vegetation conditions,” they wrote in a 2020 paper published in Rangeland Ecology & Management.
“However, our results do not support this assumption, despite repeated tests over multiple years that included both above-average and below-average precipitation ... Reduced animal weight gain in rotational grazing systems appears to be a consequence of the reduction in quality of forage consumed by cattle at high stock densities.”
After learning that cattle in the rotational pastures were gaining less weight, the USDA scientists wanted to know how the steers were grazing.
They equipped the cattle with GPS collars and sensors to track their movements and feeding habits.
“How much time was spent grazing every day, how many steps were taken (grazing speed) … and how long each animal lowered their head as a sign of eating,” says a USDA news release promoting the study.
The results showed that cattle in the rotational herds moved more slowly and more directly and ate what was available, whether it was green vegetation or not.
“They are basically just eating what is right in front of their faces, as they move,” Augustine said, adding some of the forage could be brown grass left over from the previous summer.
“If you’re grazing what’s right in front of your face, you’re going to get a lot of that dead, residual material in each bite.”
In comparison, the cattle in the continuous system roamed around the pasture and were more selective about their diet.
“What the collar data was showing … is (they are) taking more time to get bites that have more green vegetation in them and taking bites of forbs and higher quality forage species.”
The USDA scientists will continue to publish papers on the 10-year project, which comes to an end this year. They will be looking at soil health, soil carbon and other differences between continuous and rotational grazing.
“We’re waiting longer for that (research),” Augustine said.
“But I don’t see a lot of scientific research supporting an increase in soil carbon with more intensive, grazing management practices ... It may, but there isn’t strong evidence for it.”
In Canada, the federal government is promoting rotational grazing as a possible way to store more carbon in soil and reduce greenhouse gas emissions from livestock.
The feds have distributed $200 million to agricultural and conservation groups across Canada to encourage farmers to try rotational grazing, adopt cover crops and improve their management of nitrogen.
“The objective of the fund is to support farmers in adopting beneficial management practices that store carbon and reduce greenhouse gases,” Agriculture Canada says on its website.
Rotational grazing may provide some environmental benefits, but cattle producers also need to think about productivity.
If cattle in rotational systems are gaining less weight, producers need to know the financial risks. Maybe ranchers should graze their cattle in lower stock densities because a huge number of cattle in paddocks could be compromising growth rates.
“Yes, exactly,” Augustine said.
“We’re recommending that people think about this and be aware of it when they’re designing their management program.”
