Selenium deficiencies can result in high death rate

A University of California survey of mineral sufficiency of cattle breeding stock found the state's animals to be generally in good nutritional shape, but also raised a few issues worth attention.

Manganese levels are below standard in most of the animals in every area of the state, but deficiency symptoms are not widespread, which may indicate the standard should be reconsidered.

The survey also showed regional differences and ranchers in the heart of the Central Valley, in particular, might do well to take a look at their selenium programs.

"We did find regional differences, and our region has more cattle below critical levels of selenium compared to the rest of the state," said Theresa Becchetti, UC Cooperative Extension livestock and natural resources advisor in Stanislaus and San Joaquin counties. "In our region, 28% of cattle are below critical levels compared to 3, 4 and 2% of cattle in the intermountain, northern foothills and southern parts of the state, respectively."

The consequence of selenium inadequacy can be weak calves with muscle stiffness that is sometimes fatal.

"Selenium deficiency is also known as white muscle disease and affects calves, with up to a 40% death rate," Becchetti said. "Symptoms vary but can range from a weak calf not able to stand, to one standing and walking stiffly, to muscles swollen and firm to the touch. With over a quarter of the cattle in our area deficient in selenium, it would be important to check your mineral program to be sure you are providing adequate levels."

Ranchers in doubt over whether their animals have deficiencies are advised to have a conversation with their veterinarian.

"Your vet should know local deficiencies, or you can have your vet draw blood samples to check or sample your forage," Becchetti said. "Sampling the cattle is better, since what you decide looks like a good diet of forages in the pasture may not be what the cows select. They may select more or less of different forages."

If testing shows the animals are deficient, the solution is to give supplements to bring them up to par.

"Supplementation is the easiest way to bring any mineral or vitamin deficiency up to par, and there are different ways to do this through shots or providing a mineral/salt block, loose minerals or a molasses tub with minerals, all depending on what your area is deficient on and your goals," Becchetti said. "An injection ensures that each animal receives the required amount but does need more labor than a supplement you can place out in the field."

Researchers have known for decades that this deficiency can be a chronic problem in many areas of California.

"From previous work in the 1970s, we have known there is a selenium deficiency issue in the state," Becchetti said. "Our soils are deficient, which in turn causes the forage and then the animal to be deficient."

The survey also showed there may be other deficiencies worth monitoring in Central Valley breeding stock.

"Cattle in the central region are typically above critical levels for magnesium, calcium, phosphorus, potassium and sodium," Becchetti said. "Other minerals that would be of concern in our area include copper, 31% of cattle were deficient; zinc, 23% were deficient; iron; 62% were deficient; and manganese, 92% were deficient."

The manganese issue showed up in breeding cattle in every area of the state, and it is not clear why.

"Statewide, 92% of cattle were deficient in manganese, a mineral we know plays a role in reproduction, but until now we had no record of the levels in breeding cattle," Becchetti said. "Manganese deficiency can reduce the cow's ability to breed through reduced conception rates, abortions, silent heats and cystic ovaries. In addition, low levels passed to the calf cause skeletal deformities with enlarged joints, limb deformities, or the calf may be small and weak."

The question, however, is why so many animals test for deficiency of this mineral while relatively few show adverse symptoms.

"With such high levels of cattle being below critical levels of manganese, and no corresponding increase in symptoms of deficiencies, we wonder if the critical level is actually higher than what has been previously reported," Becchetti said.

The bottom line is it might be worth studying the mineral program, lab tests on the animals and symptoms of deficiency, if any, to see if remedial action is warranted.

"The levels for adequate and marginal have been established for years—some of the early work was done in the 1960s — but until this project we conducted, we had no idea what the levels in range cattle were in California," Becchetti said. "If the levels are correct, from what we found in the project, we should see more open cows (manganese affects reproduction), longer calving intervals, and skeletal deformities with calves that are born, and a big enough issue that ranchers would be complaining to their vets or livestock advisors."

Until the manganese standards are reviewed and, if necessary, revised, Becchetti advised ranchers to keep an eye out for problems with reproduction, including a look at breeding records, and to discuss with their veterinarian whether supplements makes sense.

"Our project did not follow up with participating ranches on their breeding records, but it is something we have considered for a future project," she said. "We do know from our project that manganese supplementation can easily raise manganese levels in cattle, so if ranchers are seeing issues with reproduction, they should talk to their vet about their mineral program as well as their overall health program."

(Bob Johnson is a reporter in Sacramento. He may be contacted at bjohn11135@gmail.com.)