*Dr. John D. Arthington is a professor and director of the Range Cattle Research & Extension Center at the University of Florida. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 5810 W. 78th St., Suite 200, Bloomington, Minn. 55439, or email [email protected]
A NEUROLOGICAL disease called polioencephalomalacia is a concern in feedlot cattle consuming high-sulfur diets (Jeffrey et al., 1994; McAllister et al., 1997), and this condition may result from the consumption of water containing high sulfur levels or sulfur-concentrated feed sources.
A less-recognized effect of a high dietary sulfur level is its role as a nutritional antagonist of copper and selenium, particularly in grazing beef cattle. This is a concern because copper and selenium are critical nutritional elements for all livestock.
Both elements are cofactors in numerous enzyme systems that are known to be essential for optimal growth, reproduction and immunity. Deficiencies in both elements may occur through the prolonged consumption of forages that are low in copper or selenium and/or that contain elevated concentrations of sulfur.
In addition to being a mineral antagonist, sulfur is also an essential nutrient for cattle as a component of certain amino acids, vitamins and other compounds. A sulfur deficiency in cattle is linked to decreased ruminal function, which may lead to a decline in forage digestibility and, ultimately, a decrease in animal growth.
Fortunately, sulfur deficiency is seldom a problem in well-managed grazing cow herds. Instead, diets high in sulfur are typically more of a concern. High dietary sulfur levels can lead to a reduction in cows' copper and selenium absorption. The maximum tolerable concentration for sulfur is estimated to be 0.40% of the total diet (dry matter), and concentrations exceeding this threshold are potentially harmful to cattle (Kandylis, 1984; National Research Council, 1996).
Although cattle may become tolerant of higher levels of dietary sulfur over time, concentrations exceeding 0.30% of the total diet dry matter are sufficient for the antagonism of copper and selenium to occur. Therefore, a reasonable upper limit for sulfur intake would be approximately 32 g daily for mature grazing beef cows (Table 1).
Sulfur sources
Dietary sulfur can be derived from a variety of sources, with the major contributors coming from forages, supplements and water. Because forage intake constitutes the greatest amount of total daily dry matter intake, forage sulfur concentrations tend to be the leading source of dietary sulfur.
My team's experiences suggest a common range for the sulfur content of pasture forage of 0.15-0.25%. When concentrations exceed 0.25%, an exogenous sulfur-containing source is typically responsible. This may be derived from sulfur-containing nitrogen fertilizers (i.e., ammonium sulfate) or, to a lesser extent, animal manure.
Depending on the region of focus, atmospheric deposition of sulfur can also be a contributor. This sulfur source is derived from rainfall containing weak sulfuric acid from coal-fired energy plant emissions (i.e., acid rain) and can be an important source contributing to the overall forage sulfur content.
Previously, my team investigated the impact of repeated annual applications of ammonium sulfate as a source of nitrogen on forage sulfur accumulation and the copper status of grazing cows (Arthington et al., 2002). In that study, ammonium sulfate applications resulted in plant sulfur concentrations as great as 0.50%. Cows grazing these pastures were found to have a lesser copper status (i.e., reduced liver copper concentrations) at the end of the summer grazing season compared to cows grazing unfertilized pastures or pastures fertilized with ammonium nitrate.
Supplemental feeds provided to grazing cattle can be another significant source of dietary sulfur. This has become more pronounced with the increased prevalence of dried distillers grains -- a high-sulfur feed ingredient -- in forage-fed herd supplement formulations. Several ingredients commonly found in supplement formulations contain high levels of sulfur (Table 2).
Although their contribution to total dietary sulfur intake may be significant, these feeds are typically provided only during the winter supplementation period. Fortunately, both copper and selenium can be stored in body tissues and called upon during instances of deficiency. Even though excess sulfur may reduce copper and selenium stores during periods of winter supplementation, well-managed cattle will likely have adequate tissue reserves to handle short periods of trace mineral loss. Be cautious, however, to limit the intake of high sulfur levels to as short of a time as possible to ensure that cattle have an opportunity to replenish these tissue losses.
Supplementation
In many regions of the U.S., the use of molasses-based supplemental feeds is common. Previously, I reported on the absorption efficiency of supplemental copper provided in corn-based versus molasses-based supplements (Arthington and Pate, 2002). The results indicated that the sulfur concentration present in cane molasses may interfere with normal copper absorption in cattle.
In these studies, heifers receiving supplemental copper through corn experienced a 46% increase in liver copper concentration, compared to a 9% decrease in heifers receiving the same amount of copper through a molasses supplement.
In a subsequent experiment, a third treatment was included that provided copper in a corn-based supplement but also was fortified with sulfur at a level equal to the amount obtained by the molasses supplement. Increases in liver copper concentrations were different for each treatment: 155, 87 and 13 parts per million for corn, corn plus sulfur and molasses supplements, respectively.
Other studies have shown similar responses with selenium in growing cattle consuming high-sulfur supplements. Attempts to overcome this sulfur-induced antagonism by replacing inorganic copper and selenium sources with organic alternatives have been ineffective (Arthington et al., 2003; Arthington, 2008).
Beef cow/calf producers should not avoid sulfur-containing fertilizers or feed ingredient sources because these resources are typically important contributors to economically relevant management decisions. Instead, producers should attempt to estimate the total sulfur intake of their cow herd. This can be achieved by laboratory testing both harvested and grazed forage for total sulfur.
In addition, the sulfur content of supplemental feeds can be analyzed or estimated using tabular values. From these analytical resources, a calculation of total daily sulfur intake can be estimated.
The Bottom Line
For mature grazing beef cows, total sulfur intake should not exceed 32 g daily. If this threshold is surpassed, cows will begin to experience a net reduction in copper and selenium status. Prolonged exposure to these excess sulfur conditions will likely cause a deficiency of these two essential nutrients, resulting in reduced herd productivity.
References
Arthington, J.D. 2008. Effects of supplement type and selenium source on measures of growth and selenium status in yearling beef steers. J. Anim. Sci. 86:1472-1477.
Arthington, J.D., and F.M. Pate. 2002. Effect of corn- vs. molasses-based supplements on trace mineral status in beef heifers. J. Anim. Sci. 80:2787-2791.
Arthington, J.D., F.M. Pate and J.W. Spears. 2003. Effect of copper source and level on performance and copper status of cattle consuming molasses-based supplements. J. Anim. Sci. 81:1357-1362.
Arthington, J.D., J.E. Rechcigl, G.P. Yost, L.R. McDowell and M.D. Fanning. 2002. Effect of ammonium sulfate fertilization on bahiagrass quality and copper metabolism in grazing beef cattle. J. Anim. Sci. 80:2507-2512.
Jeffrey, M., J.P. Duff, R.J. Higgins, V.R. Simpson, R. Jackman, T.O. Jones, S.C. Mechie and C.T. Livesey. 1994. Polioencephalomalacia associated with ingestion of ammonium sulphate by sheep and cattle. Vet. Rec. 134:343-348.
Kandylis, K. 1984. Toxicology of sulfur in ruminants: A review. J. Dairy Sci. 67:2179-2187.
McAllister, M.M., D.H. Gould, M.F. Raisbeck and B.A. Cummings. 1997. Evaluation of ruminal sulfide concentrations and seasonal outbreaks of polioencephalomalacia in beef cattle in a feedlot. J. Am. Vet. Med. Assn. 211:1275-1279.
National Research Council. 1996. Nutrient Requirements of Beef Cattle. Seventh rev. ed. National Academy Press, Washington, D.C.
|
1. Amount of sulfur derived from pasture forage containing a range of sulfur concentrations (dry matter basis)* | ||
|
Forage |
Intake, |
Sulfur |
|
sulfur, % |
lb./day |
intake, g/day |
|
0.15 |
20 |
14 |
|
0.20 |
20 |
18 |
|
0.25 |
20 |
23 |
|
0.30 |
20 |
27 |
|
0.35 |
20 |
32 |
|
*Assumes a 1,000 lb. cow consuming 2.0% of bodyweight in dry matter forage daily. Daily sulfur intake should not exceed 32 g per day for mature beef cows. | ||
|
2. Amount of sulfur derived from feedstuffs commonly supplemented to cow herds in Florida* | |||
|
|
Intake, |
Sulfur, |
Sulfur provided, |
|
Item** |
lb./day |
% as-fed |
g/day |
|
Molasses (heavy mill run) |
5.0 |
0.70 |
16.0 |
|
Molasses, 32% |
3.5 |
0.70 |
11.0 |
|
Brewers grains |
5.0 |
0.36 |
8.0 |
|
Distillers grains |
5.0 |
0.40 |
9.0 |
|
Corn gluten feed |
5.0 |
0.23 |
5.0 |
|
Soy hulls |
5.0 |
0.10 |
2.0 |
|
Citrus pulp |
5.0 |
0.07 |
1.5 |
|
*Daily intake values are selected estimates for commonly used supplementation rates. If your supplementation rate differs, then actual sulfur intakes will also differ. | |||
|
**Liquid molasses values provided by United States Sugar Corp., Clewiston, Fla., for molasses derived from sugarcane processing (June 18, 2007). Dry feed values derived from National Research Council (1996). | |||
Volume:85 Issue:15