Blue-green algae blooms in ponds also can occur in hot weather. They are most common in ponds with high organic matter, such
as ponds where cattle are allowed to wade, or where fertilizer runoff occurs. The blue-green algae accumulate along pond edges,
especially in windy conditions, exposing cattle when they drink. Both the live and dead algae are toxic. The toxins can affect
the neurologic system, causing convulsions and death, sometimes next to the source. They can affect the liver, causing a delayed
syndrome of weight loss and photosensitization (skin peeling in sparsely haired or white-haired areas).
Perilla mint causes acute bovine pulmonary edema and emphysema (ABPE), usually in late summer. It grows in most of the central
and eastern United States and is common in partial shade in sparsely wooded areas, and around barns and corrals. There is
no treatment, so prevention is critical.
Lantana is a common ornamental plant that spreads readily to pastures from birds carrying seeds. Lantana is highly toxic and
causes damage to the liver. Common signs include weight loss and photosensitization.
Cattle with access to wooded areas may eat braken fern. Cattle must eat roughly their body weight over time before toxicity
occurs, but may do this in situations where other forage is not available. Braken fern toxicosis causes aplastic anemia. Fever,
anemia, hematuria and secondary infections are some of the most common signs.
Once the rains come, watch out for cocklebur and ABPE.
As summer moves into fall, the potential for acorn toxicosis increases. Cattle usually have to eat large amounts to become
sick, but those that are in poor body condition and hungry are more likely to do so. Clinical signs include constipation or
dark, foul-smelling diarrhea, dark nasal discharge, depression, weakness and weight loss.
Acorns are toxic to the kidneys, so a high creatinine will be noted on blood chemistry. Once the rains come, other plant toxicities
may occur. Cocklebur may sprout as waters recede. The two-leaf stage can cause acute liver failure, and if there is little
other forage available because of prolonged drought/overgrazing, cattle may eat toxic amounts. Cattle moving from poor forage
conditions to immature lush pasture can have ABPE. Slow introduction to lush forages will decrease the potential for problems.
The lack of summer forages and the need for supplemental feeding during a drought can increase the likelihood of feeding "accidents"
and toxicities. Producers may be tempted to feed cattle ornamental plant clippings, many of which are highly toxic. Grain
overload also is a potential problem if access to concentrate feeds is not controlled. Salt toxicity can occur if hungry cattle
are allowed free access to high-salt-containing "hot mixes."
Even though these mixes are meant to limit intake, an initial feeding can be high enough to cause toxicity in starved or salt-deprived
cattle. Feeding byproduct feeds, candy, bread, screenings, etc., also may be more common, all of which have the potential
to cause problems. Producers may be tempted to feed moldy hay or feed, which can lead to toxicity problems.
Christine Navarre, DVM, MS, Dipl. ACVIM works as an extension veterinarian with Louisiana State University's Departme nt of