In the past we have discussed the need for various minerals in the diet of cattle, both growing and mature. Just as certain amounts are needed in the diet, these same minerals can create a whole host of problems when received in excessive amounts. Over the last couple of years sulfur levels in forages and feeds has come under scrutiny for a number of reasons. This article will review some of the recent information that has been generated and outline what producers should be aware of with this problem.
Remember that sulfur (S) is an essential dietary mineral element. It is crucial for optimum rumen microbial growth and for digestion of feeds. It is a component of the essential amino acid, methionine, as well as other amino acids and is found in other compounds in the animal's body and milk. This means that like so many other nutritional components, while the appropriate amount is vital to normal performance and productivity, excessive amounts are where the problems lie.
The recommended dietary concentration of S is 0.15 percent of the total ration dry matter for most beef animals. Some recent research has indicated that S levels in the diet of .1 to .12 percent may be adequate. The maximum tolerable level for S is estimated to be 0.4 percent. Research reported in the Beef NRC (National Research Council) indicated that increasing sulfur levels in beef cattle diets from .12 percent to .41 percent resulted in a decrease in feed intake of 32 percent. This problem can be compounded in situations where water sources carry higher sulfate levels (5000 ppm) resulting in an overall excess in S intake.
· reduced feed intake
· gaunt and unthrifty appearance
Less visible symptoms include an interference with absorption of dietary copper and selenium as well as other minerals. In situations where the excessive intake become severe enough it appears that the high S intake can be related to outbreaks in polioencephalomacia (PEM), a nervous system disorder. PEM tends to occur with greater prevalence in growing or feedlot cattle.
In a case study in Michigan, subclinical sulfur toxicity was suspected in dairy cows and heifers. These cattle exhibited many of the symptoms listed above although they were unable to verify the apparent toxicity clinically from abnormally high rumen or blood S concentrations. The common factor appeared to be high S (.3 to .4 percent S) in forages and rations fed to the animals for three to four months. Nonetheless, it is useful to characterize what was observed so that other producers can evaluate their feeding and forage crop fertilization programs to try to avoid potential problems that may be caused by S toxicity.
Dr. Steve Blezinger is a consulting nutritionist with an office in Sulphur Springs, Texas. He can be reached at P. O. Box 653 Sulphur Springs, TX 75483. By phone at (903) 885-7992 or by e-mail at email@example.com