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The biological risk of drought

Melissa Bravo for Progressive Forage Published on 09 July 2021
corn field

The grazing season was well underway in the southern U.S. when tornadic weather spawned in early May. Across the country, 14 states have declared worsening drought stages in the peak of calving season.

Meanwhile, the convection of Gulf Coast precipitation continues to rain down excessively on cow-calf grazing acreage east of the Mississippi. Unlike breaking weather news, there is no coordinated effort nationally that tracks and tabulates livestock illnesses and mortalities as they occur in real time. But we can look at our collective migration histories, and data compiled from recent historical droughts, to prepare for what will come to pass.

The megadrought in Australia lasted from 1891 to 1903. Tens of millions of livestock died from disease, starvation and thirst across a third of the country. The 2012 drought and migration of cattle from Texas to Nebraska resulted in the largest national herd reduction in 60 years. The seven-year drought-ending floods in Queensland in 2019 killed more than half a million cattle. When unrelenting droughts occur, dust and sand-vectored microbes are spread vast distances and are responsible for millions of animal and human illnesses.

Fewer and fewer Americans can visualize the devastation of the megadrought that occurred in the U.S. in the Texas Panhandle and western Oklahoma in the 1930s. It is hard to accept that over one hundred million acres of topsoil just blew away, and the drought did not end until 1939. But these drought-ending rains also sporulated harmful bacteria. The 1957 outbreak of anthrax in Oklahoma killed more than a thousand livestock and bears, testament to the longevity of toxicogenic bacteria in grazing systems. To “hear” this firsthand, listen to the Amplified Oklahoma, Episode 47, “Anthrax Outbreak.”

When things go wrong

The infection and/or the inflammatory response to the infection can be lethal. Localized infections may start out as just a skin puncture but can become systemic if the bacteria or toxin cross over into the blood and lymphatic system. If it only takes less than a minute for blood to circulate from the heart all around the body and back to the heart again, one can imagine how quickly problems with breathing, abnormal heart rhythm, falling body temperature, extreme weakness and unconsciousness can manifest. A systemic infection can go from septic to sepsis to severe sepsis to sepsis shock very quickly. So quickly, antibiotics may not have time to act.

Bacterial infections most concerning to grazing livestock

  • Bacillus species – Bacillus bacteria are spore-forming bacteria. There are more than 200 species of bacillus. About two dozen are known to cause illness in animals, including humans. These species that include anthrax have been increasingly implicated in a wide range of infections including “abscesses, bacteremia/septicemia, wound and burn infections, ear infections, endocarditis, meningitis, ophthalmitis, osteomyelitis, peritonitis, and respiratory and urinary tract infections”.
    —Medical Microbiology, Chapter 15.

  • Anthrax – We often read that favorable weather conditions increase the risk of anthrax to grazing animals. But what does that mean exactly? Many have reported on the frequent association of outbreaks of bacillus infections in grazing animals after a period of extensive drought ends with an abundance of rain. Unfortunately, this is the scenario that will occur in much of the grazing lands across the western U.S. And many of these areas are known to have historical cases of anthrax losses. A recent global anthrax map published by Dr. Blackburn and associates from the University of Florida’s Emerging Pathogens Institute in a Nature Microbiology Journal paper is useful to visualize where in the U.S., and the world, livestock may be exposed to this soil bacterium.

  • Clostridium species and botulism – Clostridia is the other sporulating toxicogenic bacteria that, in the presence of oxygen, rapidly reproduces. And when infection occurs, these bacteria release life-threatening toxins. Speaking of “fowl” weather, did you know in addition to causing deaths of livestock and the disease known as “blackleg,” mass deaths of waterfowl are often caused by clostridia infections? “A significant association was found between the number of dead birds recorded in each botulism outbreak and the mean temperature in July,” when temperatures were above 78.8ºF.
    —Environmental Factors Influencing the Prevalence of a Clostridium

The largest risk of clostridia infection comes from contamination of forage and feed from dead animal, bird and snake carcasses. In the aftermath of tornadic weather that has damaged stored grains and ensiled forages, weigh the risk of feeding contents. Clostridia are fermenters, and ensiled forages undergo fermentation. In dried grains that have gotten wet, spoilage is “fermentation.” Clostridial vaccines have been available since the 1930s. Don’t wait until the rains come. If proper vaccination protocols are followed including required booster shots, calves and cattle should acquire lifetime immunity.

A few other forage-soil bacterias to be concerned about are campylobacter, escherichia, haemophilus, leptospira, listeria, mannheimia, pasteurella, pseudomonas, salmonella, shigella, staphylococcus, streptococcus and yersinia. Most of these are recognizable as also being a risk to humans. Excessive precipitation is often a precursor to these infections. Some proliferate in cold and wet, others in hot and humid. Either way, calving during inclement weather or shortly thereafter increases the risk of vaginal and birthing fluid bacterial transmission to dams of many of these pathogens. The longer adverse conditions persist, the more likely these infections will arise. Therefore, it is essential to have a relationship with a veterinarian who can advise you on the vaccinations recommended to protect your herd.  end mark

Getty Images.

This is the second part of a series about foraging through the weeds of climate change. Read part 1 "Adverse weather impacts essential nutrient uptake".

References omitted but are available upon request. Click here to email an editor.

Melissa Bravo

  • Melissa Bravo

  • Assistant Professor, Agronomy and Livestock
  • Rutgers Cooperative Extension
  • Email Melissa Bravo

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