Water is a vital nutrient that we take for granted. We assume that if water is available, we’ve taken care of that requirement. However, there are a number of factors that can negatively affect water quality and livestock performance. So far we’ve talked about cyanobacteria and nitrates. This time, I’ll cover sulfates.
Rumen microbes need sulfur for growth and metabolism. Sulfur is needed to make sulfur-containing amino acids (methionine, cysteine and homocysteine) as well as thiamine and biotin. However when excessive amounts of sulfur are present (greater than the ability of the rumen microbes to utilize it), the excess sulfur is absorbed into the bloodstream as sulfides. As sulfate level in the total diet increases, from water, feed and/or forage, the level of sulfide in the rumen increases. This can cause a number of problems.
Sulfides in the body can lead to necrosis of neural tissues. This is thought to be the primary cause of polioencephalomalacia (PEM). In addition, some sulfur-compounds can destroy thiamine activity. Additionally, sulfides interfere with trace mineral availability. The sulfides bind with copper in the rumen making it insoluble, thus increasing copper requirements for ruminants. Selenium utilization by livestock is antagonized by high sulfates, by increasing the excretion of selenium. Sulfur also negatively interacts with zinc and calcium absorption.
So when do you need to be concerned about sulfates in water? Testing is the only way to determine the safety of your water source. Signs of a sulfate related problem will change with the level of sulfates in water as shown in the table below.
Sulfate level in water
1,500 – 2,000 ppm Reduced water intake, diarrhea, decreased performance
2,000 – 2,500 ppm Maximum tolerated intake (provided feed level is low)
3,000 ppm and over Reduced feed intake, weight gain, possible water rejection, PEM, possible death
Cattle can be acclimated to tolerate higher levels of sulfates in water. Diluting high sulfate water with low sulfate water is a good option for newly received cattle. The upper limit for calves is 500 ppm sulfates and 1000 ppm for adult cattle. Sulfate/sulfur levels of the feed that cattle consume also needs to be taken into consideration as they will compound each other, just like nitrates. Sulfur intakes of 0.3% of diet dry matter or less are considered safe for all classes of cattle. Cattle on forage based diets have been able to safely tolerate as much as 0.5% of dry matter intake.
In summary, excess sulfur in water is a hazard to cattle. Testing is the best way to know where sulfate levels are for water and feeds. Contact your county extension service for advice on proper sampling techniques and testing options.
