News from the Midwest Sectional Meetings, March 16-18, 1998, Des Moines, Iowa
Contact:
Don Mahan, Ohio State University (614) 292-6987
By Kyle Sharp
Low Dietary Selenium, Vitamin E Affect Boar Performance
If a boar has had trouble fertilizing sows or gilts, or if the litters it has fathered have been small, its diet may be too low in selenium or vitamin E, said Ohio State University animal scientist Don Mahan.
Low levels of these two elements in a boar's diet, especially selenium, can lower boar semen quality.
In boar sperm, selenium helps form the thick part of the tail where it attaches to the head. A strong, straight tail is what moves sperm along the reproductive tract to the sows' and gilts' eggs. If a boar's diet is low in selenium, sperm may form what is called bent or shoehook tails. These abnormal tails slow sperm movement and make fertilization more difficult.
"It's like trying to walk around with a broken leg," Mahan said.
In research conducted by Mahan and other Ohio State animal scientists, boars fed a diet low in selenium were compared to boars fed a selenium-fortified diet. The selenium-fortified boars had nearly 62 percent normal sperm, while the selenium-deficient boars had less than 25 percent of their sperm with normal, straight tails.
The fertilization rate of the two boar types also was tested by inseminating gilts and measuring how many eggs were fertilized. The sperm from the selenium-fortified group fertilized nearly 99 percent of the eggs they encountered, compared to less than 74 percent by the unfortified group.
Low levels of vitamin E in a boar's diet also can affect sperm quality, but not nearly as much as selenium, Mahan said. It acts as an antioxidant within boar semen. Antioxidants prevent free oxygen in a boar from damaging sperm cells.
"Vitamin E helps protect the cell membrane of sperm from damage, while selenium prevents abnormalities in sperm tails," Mahan said.
Tests showed that boars fed a diet fortified with vitamin E had nearly 45 percent normal sperm, while an unfortified diet resulted in less than 42 percent normal sperm. However, the fertilization rates of the two vitamin E groups were similar.
"Low dietary vitamin E didn't seem to have as great an effect on sperm cell movement and quality as selenium, but it did improve the percentage of normal sperm," he said. "This study emphasizes the fact that these two nutrients, especially selenium, must be fed in order to maintain reproductive performance."
Selenium deficiencies in livestock can be common in Ohio. Years of high crop production in the state have depleted soils of selenium, and high rainfall levels wash selenium from the soil. Because there is less selenium in the soil, there is less to be absorbed into crops and eventually fed to animals.
"We're more likely to encounter selenium deficiencies in our livestock than people in the Central United States," Mahan said.
The switch from raising hogs in pastures to complete confinement operations also has contributed to lower selenium levels. Pigs used to get some of their selenium supply directly from the soil because of their rooting nature, but when they're raised in a building that's not possible, he said. Once they are moved inside, they become completely dependent on what is supplied in their diet.
Most hogs are being fed diets fortified with 0.3 ppm selenium that provide enough of the element to maintain good sperm quality. If a producer suspects a boar is selenium deficient, the expense and time to have the animal tested isn't practical. The best way to cure the problem is to feed it a selenium-fortified diet. Once an animal is fed a selenium-fortified diet, it takes 60 days for the deficiency to be corrected, Mahan said.
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