Can I Graze Smut Grass?

August, 2020
 Aaton Stam, UF/IFAS Seminole Tribe of Florida, Brighton

Several years ago I was involved in a field trial, looking at the nutritional value of smut grass. The data we collected was surprising to many, and to this day, is a topic that is widely debated/discussed among the cattlemen I consider my friends. Many ranchers feel smut grass is a weed that should be killed without mercy, while others have looked at the vigorous growth and nutritional value to be an asset on their ranch. I believe both outlooks are correct, and grazing smut grass is definitely not for everyone.  If  smut grass is to be an asset, I believe a strict grazing schedule must be maintained. Simply put, cattle on pasture for 7 days and 21 days off. The cattle should be returning to pastures where the smut grass is no older than 21 days.  This ensures the smut grass is still palatable during the entire week they are on the pasture.  Our results from our initial field trial were that fertilized smut  grass (50# of Nitrogen) had an average crude protein of 16% on a dry matter basis and a total digestible nutrient (TDN) value of 56. Our control (no fertilizer) smut grass averaged 13% crude protein and a TDN of 56.5. The pastures we used for this experiment had very little bahia grass, so we were not able to do a cross comparison of smut grass quality vs bahia quality.

I have been running a field trial with the cooperation of the Seminole Tribe of Florida utilizing various groups of cattle to test the ability of cattle to graze smut grass and utilize it as forage. We have tested the data from the nutritional study to see if cattle would be successful in utilizing the smut grass in a pasture environment. Although the acreage was small in size, we feel the numbers are easily replicable over larger ranches and operations.  We initially stocked the 20 acre pasture, known as Pasture X with 40 head of 2 year old heifers. The pasture was nearly completely covered in smut grass, with small areas of bahia. The pasture was divided into (4) five acre paddocks. Cows were given 7 days of grazing on each paddock and then rotated to a new 5 acre pasture. We saw the 2 year old heifers were able to thrive on the 21 day old smut grass and had a 93% conception rate and 78% calf crop (live calves). The cost per heifer was $469 in year one and $479 in year two. These costs included veterinary expenses, mowing, fertilizer and spreading, 90 days of feed prior to bulls arriving, molasses with mineral package, labor (day work and administrative fees). These costs were in line with the average costs on neighboring heifers, but the cost per acre was significantly lower as the stocking rate of 2 animals per acre was significantly better than the 1 animal unit to 2.5 acres that is typical of many south Florida ranches.

Last September (2019), we tried a group of 80 feeder calves, averaging around 450 pound on Pasture X to monitor their average daily gain utilizing smut grass as their primary forage. Molasses with mineral supplementation was available at all times for these calves.  The calves were unable to convert the smut grass in a way that would make raising stocker calves profitable in south Florida. We believe the smaller calves were not able to utilize the smut grass, based on their rumens not being completely developed. Most calves have a fully developed rumen by 6-9 months of age. The ADF (acid detergent fiber) primarily cellulose, lignin and other fibers were not able to be broken down by the smaller calves.  We did notice the larger calves, 600 plus pounds, performed better in the trial, but the overall average daily gain for all of the calves was less than one pound.

We were able to compare nutritional value of smut grass and bahia grass from Pasture X during this field trial. The pasture was given 50 pounds of nitrogen in September, prior to calves being turned out. The following numbers are all in dry matter (DM), and all samples were taken when the grass was 21 days old:  In November, the smut grass was 10.0% crude protein (CP), with a TDN of 60 while the Bahia grass was 10.1% CP and had a TDN of 48. In January the smut grass’s CP was 15.2% and TDN of 60, while the Bahia was 19.6% CP  and TDN was 63. In April, the smut grass analysis was 11.5% CP and TDN of 57, while the bahia’s CP was 14.4% and TDN was 60.

 

The heavy stocking rates throughout Pasture X’s existence has reduced the overall prevalence of the smut grass in Pasture X.  Pasture X was initially almost exclusively smut grass, and is now approximately 50 percent smut grass and 50 percent bahia, with various broadleaf weeds and white clover being present in all paddocks.

In conclusion, we have seen smut grass can be valuable forage, if managed properly for cow/calf operations. Based on the stocker calf field trial, I do not believe smut grass would be appropriate for stocker calves.  The calves were not able to convert the forage into the average daily gains that would be required of a stocker type operation. If you have any question about smut grass grazing or Pasture X grazing trials, expenses or additional nutritional analysis, please feel free to contact Aaron Stam at astam@ufl.edu.

 

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