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Well-known member
Jan 20, 2007
LaRue, Ohio
Choosing Summer Annual Forage Crops to Reduce Risk of Nitrate Toxicity

By Glenn Selk

Annual forage crops like forage sorghums make valuable contributions to the hay supplies in Oklahoma. They are well adapted, very productive and provide high quality forage. However, some of these plants accumulate toxins that can result in costly livestock losses. 
Nitrate is the primary nutrient form of nitrogen in most soils and is a normal constituent of plants. Normally nitrate is assimilated so rapidly following uptake from soil that its concentration in plant tissues is low. Occasionally, excessive levels occur in plants. The most notorious accumulators of nitrate in Oklahoma are the plants in the sorghum family including johnsongrass. Other annuals that on rare occasion accumulate nitrate are small grains (wheat, oats, rye and barley). Some perennial grasses (bermudagrass, fescue) very rarely have been reported to accumulate high levels of nitrate.  Certain weeds (pigweed, mustard, nightshade and lamb's quarters) also can contain dangerous levels. 
Accumulation is usually triggered by some environmental stress, where plant growth is restricted but absorption of nitrate from soil continues. The most common stress of summer annuals is drought. Lack of moisture, together with excessive soil nitrogen for existing growing conditions, is a frequent cause of toxic levels of nitrate in sorghums.
The level of nitrate that causes toxicity in ruminants varies depending on rate of intake, diet, acclimation to nitrate and nutritional and reproductive status. As a rule, forage containing less than 5,000 ppm nitrate on a dry matter basis is safe for non-breeding cattle. Forage containing 5,000 to 10,000 ppm nitrate is considered a potential source of production loss when provided as the only feed. Production losses are usually manifest as reduced milk production and lowered reproductive performance.  Forage containing over 10,000 ppm nitrate is considered dangerous, and potentially lethal.  These high concentrate forages often can be fed safely after proper dilution with other feeds.
Questions among cattle producers and hay growers about the potential nitrate accumulation in various forages caused the following experiment to be conducted and reported.

During the summer of 1990, 17 varieties of Sorghum x Sudan, 12 varieties of Sorgo x Sudan, five varieties of Sudan x Sudan hybrids, and six varieties of Pearl Millets were being grown at three Oklahoma State University Agronomy Experiment Stations for yield evaluations. The second year of the study was conducted in 1991 with 18 varieties of Sorghum x Sudan, nine varieties of Sorgo x Sudan, two varieties of Sudan x Sudan hybrids and five Pearl Millets. Field locations were: Eastern Oklahoma Agronomy Experiment Station at Haskell, OK in Muskogee County; South-Central Oklahoma Agronomy Experiment Station in Grady County near Chickasha; and the Southwestern Oklahoma Station near Tipton in Tillman County.  The following table lists the average nitrate concentration of hay samples collected from these plots over the two summers.  Obvious differences in locations are apparent, reflecting differences in soil type and soil moisture in those two growing seasons.  Equally apparent is the fact that pearl millet consistently accumulated nitrate at greater concentrations than did the other forage types. 

Table 1. Least squares means (averages) for nitrate concentration in ppm for four types at three locations. 
Forage type                                                                                    Location

                              Eastern(near Haskel)              South-Central  (near Chickasha)              Southwest  (near Tipton)

Sorghum x Sudan        7795                                                3302                                                        7049

Sorgo x Sudan            7291                                                  3255                                                        6673

Sudan x Sudan            8079                                                  3461                                                        7190

Pearl Millet                  14122                                                6572                                                        10534

Selk, et al. Prof. Animal. Scientist. Vol 11: 20 - 25
Millets have been shown in other research to be much less prone to accumulate a different toxin called prussic acid.  Prussic acid will tend to dissipate when the crop is cut for hay and, if allowed to cure thoroughly, will be reduced extensively.  Therefore, if the summer annual, that producers plan to plant this spring, is targeted to be a hay crop,  it makes sense to plant one of the other forage sorghums, not the pearl millets.  Planting one of the other forage sorghums does NOT eliminate the risk of nitrate toxicity (but does reduce it), AND if grazed after stress such as frost or drought may accumulate prussic acid.

Producers are strongly encouraged to plan the use of the crop before they select and plant the seed.  Learn more about nitrate toxicity in livestock by reading OSU Fact Sheet F-2903.

Observe Bulls Closely as Breeding Season Begins

By Glenn Selk
A good manager keeps an eye on his bulls during the breeding season to make sure that they are getting the cows bred.  Occasionally a bull that has passed a breeding soundness exam may have difficulty serving cows in heat, especially after heavy service.  Inability to complete normal service and low fertility are more detrimental than failure to detect cows in heat to calf crop percent.  Such problems can best be detected by observing bulls while they work.  Therefore producers should (if at all possible) watch bulls breed cows during the first part of each breeding season.  If problems are apparent, the bull can be replaced while salvaging the remainder of the breeding season and next year’s calf crop.  Likewise a small proportion of bulls can wear out from heavy service and lose interest. These, too, will need to be replaced.  The greater the number of cows allotted to each bull in the breeding pasture the more critical it is that every bull be ready to work every day of the breeding season.

Injuries to bulls during the breeding season are relatively common.  When a bull becomes lame or incapable of breeding, because of an injury to his reproductive tract, he needs to be removed from the breeding pasture and replaced with another bull.


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