Geni Wren Many areas of the country that experience drought this summer are now being relieved with some rain, which can bring its own special issues with regrowth of lush grass.
Tom Troxel, PhD, University of Arkansas, says regrowth of sorghums or johnsongrass after these rains can poison cattle because they are high in prussic acid (hydrogen cyanide [HCN]).
Troxel offers these precautions for using sorghums or johnsongrass:
- Do not allow animals to graze fields with succulent, young, short growth. Graze only after plants reach a height of 18 to 24 inches.
- Do not harvest or feed drought-damaged plants in any form, regardless of height, within four days following a good rain. It is during this period of rapid growth that an accumulation of HCN in the young tissue and of nitrates in the stems is most likely to occur.
- Do not graze wilted plants or plants with young regrowth. Do not rely on drought-damaged material as the only source of feed. Keep either dry forage or green chop from other crops available at all times. Even when this material is mildly toxic, it can be fed safely to animals receiving some other forage or grain source. Uneven growth of hybrids as a result of drought can best be utilized as silage.
- Do not use frost-damaged sorghum as pasture or green chop during the first seven days after the first killing frost. Delay pasturing for at least seven days or until the frosted material is completely dried out and paper brown colored. Do not rely on frosted material as the only source of feed. The toxin is usually dissipated within 48 hours. Do not graze at night when frost is likely.
- Do not turn hungry cattle onto a pasture of sorghum, sorghum-sudan hybrid or johnsongrass. Fill them up on hay first, and begin grazing in the late afternoon.
- Prevent selective grazing of the young regrowth, which may be highly toxic, by rotational grazing of small pastures that may be grazed down to a six-inch stubble within a ten-day period. This will mean cross fencing to provide short-term rotational or strip grazing.
- Silage may contain toxic quantities of HCN, but it usually escapes in gaseous form while being moved and fed. If frosted forage is ensiled, allow fermentation to take place for at least six to eight weeks before feeding.
- The HCN potential of hay decreases during the curing stage and is only dangerous if hay is improperly cured.
Animals affected by prussic acid poisoning may be treated with a sodium nitrite-sodium thiosulfate combination. It must be injected intravenously and very slowly. The dosage and method of administration are critical. Consult a veterinarian to correctly diagnose prussic acid poisoning and to determine the proper treatment.
Another summer problem is blue-green algae (read more here). “We’ve had some cases were we’ve suspected blue-green algae toxic problems,” Troxel says. “It’s the time of year when we can see problems and with the drought it makes more reason to be on the alert.”