CORVALLIS, Ore. – A new study by Oregon State University researchers has found that adding selenium to fields planted with alfalfa will allow the perennial forage crop to “take up” the important mineral in its tissues, providing better feed for calves and other livestock.
The findings are particularly important, researchers say, because selenium delivered through plants in an organic form is much safer than directly feeding selenium to calves in an inorganic form, such as salt.
Results of the study have been published in part in the journal PLOS One.
Selenium is a naturally occurring mineral that is found in heavy concentrations in some parts of the country, and at low levels in others – including Oregon. Ranchers often provide selenium in supplements to livestock, but applications must be done carefully because too much of the mineral can be harmful to animals.
“When selenium gets picked up by the plant, it goes right into the amino acid selenomethionine, and when the animals consume it, the selenium gets stored in the muscle in a benign way,” Hall said. “The ranchers we’ve spoken with are extremely interested in these results, because not only does it appear this is safer for the animals, it may be cost-effective as well.”
During field trials, selenium was applied at varying levels to alfalfa hay fields after the first of three scheduled cuttings. Regardless of the level of selenium applied, the plants had taken up 83 percent of the selenium by the time of the second cutting. The remaining 17 percent of the applied selenium was taken up in the alfalfa by the third cutting.
The percentage of selenium uptake by the alfalfa was consistent regardless of the amount applied, according to Hall. “If we doubled the amount of selenium, the plants took up twice as much,” she said.
The researchers then fed selenium-fortified alfalfa to calves and compared their growth to control animals. Several weeks later, the calves with supplemented diets had higher blood selenium content levels at a rate commensurate with the amount of selenium applied to the fields. The calves fed selenium-fortified alfalfa also weighed up to 10 percent more than calves fed alfalfa without selenium.
Weight growth by the calves increased with additional selenium, Hall said, though there was more variability than the linear response by the plants.
“We also tested weaned calves to see if selenium-fortified alfalfa might boost the efficacy of vaccinations, giving a boost to the animals’ immune system,” Hall said, “and it appears that is the case. Calves fed the selenium-fortified alfalfa had increased antibody production – at a rate that mirrors the amount of selenium applied.
“The study demonstrates that selenium-fortified hay boosts the growth and vaccination response of weaned beef calves, which results in decreased mortality and improved slaughter weights,” she added.
Hall is a fifth-generation Oregonian who comes from a cattle ranching family in Douglas County. She is part of a long history of selenium studies at OSU that go back 50 years.
“Oregon is the only state where you can artificially fertilize fields with selenium,” Hall said, “and because most areas of the state are deficient in the mineral, this may be a strategy to consider for ranchers. Some countries, including Denmark and Finland, require fertilization in fields to increase the amount of selenium in the food chain, so the precedent is there.”
Other authors on the paper, all from OSU, include Gerd Bobe, Janice Hunter, William Vorachek, Whitney Stewart, Jorge Vanegas, Charles Estill, Wayne Mosher and Gene Pirelli.