National Study Shows Southeast U.S. Beef Cattle Struggle With Selenium Deficiency
Livestock Update, January 1997
Dr. Dee Whittier, Extension Veterinarian, Beef Cattle
Virginia-Maryland Regional College of Veterinary Medicine
Cow/calf producers in Virginia have become very aware that selenium was an essential dietary element for cattle. Selenium deficiency can result in white muscle disease, retained placenta, infertility, abortion, sudden death, and premature or weak calves at birth. A recent survey has provided some new information about selenium deficiencies in the United States.
The USDA's National Animal Health Monitoring System (NAHMS) tested whole-blood samples from 2,216 cows and heifers in 253 herds during the 1992 Cow/Calf Health and Productivity Audit (CHAPA). CHAPA herds were from 18 states, including Virginia, that contained 70 percent of the adult United States beef cow inventory in January 1993. Of the whole-blood samples collected from cattle during the CHAPA, 7.8 percent were classified as severely deficient for selenium, 0-.050 parts per million (ppm). Another 10.4 percent were marginally deficient (.051 -.080 ppm).
These CHAPA results showed a wide variation among regions. Percentages of severely deficient cattle ranged from 3.6 percent in the central region to 18.6 percent in the southeast. Only 62.7 percent of the operations in the southeast had no animals in the severely deficient range compared to 89.7 percent and 94.6 percent in the west and central regions respectively. The mean of all samples collected on a farm were used to classify each according to criteria used for the individual blood samples. Overall, 4.7 percent of operations were considered severely deficient and another 9.1 percent were marginally deficient. In the southeast, 36% of herds were classified as severely or marginally deficient.
Does giving selenium supplements to beef cattle protect against deficiency? Forty-nine percent of all operations supplemented selenium for their herds. Nearly all of these (98 percent) supplemented by using a mineral supplement with additional selenium. About 4 percent gave selenium injections and 4 percent added selenium to their cattle rations. Some operations used more than one method of supplementation. Supplementation was more common in the central and southeastern regions (54.7 and 61.4 percent of herds in these regions, respectively) than in the west (19.0 percent). Analysis of forage samples collected during the CHAPA showed lower levels of selenium in the southeast region while levels were considerably higher in other areas of the U.S.
Percentages of severely deficient cattle were lower in all regions for operations that supplemented selenium, supporting the value of supplementation. However, the results show that, particularly in the southeast, supplementation procedures are frequently inadequate. While operations that supplemented with selenium in the central region of the U.S. had no deficient animals, operations with some selenium supplementation in the southeast still had over 16 percent of individuals that were considered severely deficient.
CHAPA results showed that selenium supplementation does not ensure adequate selenium levels in all cattle. Inadequate supplementation levels for the herd's needs and erratic individual animal consumption are two possible explanations. There are large differences in free-choice salt/mineral mixes and in the tendency of cattle to consume them. While there are legal limits in the concentrations of selenium that products contain, many supplementation products contain much less than the legal limit. This tendency to be cautious probably comes from an influence of the practices of other U.S. regions where soils contain so much selenium that toxicity may occur. Virginia producers should work with their veterinarians and nutritionists to assure that cattle are receiving adequate supplementation so as not to risk the production losses associated with a deficiency in selenium.
(See printed copy of January 1997 issue of Livestock Update for graph)