I'm in the middle of reading a book by Timothy Egan called “The Worst Hard Time.” If you're interested in American history surrounding the plight of the farmers and townspeople of the Oklahoma and Texas panhandles during the Dust Bowl years of the 1930's, this is a great read.
I had heard stories of the “dirty thirties” from my grandparents, who lived through this era on the farm in Brown County. Their stories of dry fields and dust clouds seemed like they came from a different world. In his book, Egan does an extraordinary job of bringing these stories to life. You can almost taste the dust in your mouth and feel it in your eyes, as he recounts the “dusters”. These enormous storms lifted topsoil from bare ground and carried it hundreds of miles to rain down and blow in on houses, barns, and roads in the country as well as in the economically depressed cities of the Plains.
As a veterinarian, the most interesting passages of the book had to do with the effect of dust on the livestock. Cattle out on the plains already had many strikes against them: malnutrition from poor feed and a lack of good water. Then throw in days upon days of dust storms. The dust suffocated some cattle outright and blinded others.
Flash forward to 2012. This summer's drought has been compared with the dust bowl years, with record low rainfall during the summer months in many parts of the region. While it's as dry now as it was then, at least we are not dealing with the “dusters” of yesteryear. Modern conservation practices and a spring that allowed fields to start growing crops have taken those out of the equation, fortunately.
Yet, dust remains a scourge for cattle producers this year. Young calves, whether still on pasture or just weaned, have been exposed to dusty conditions on pasture and in drylots. The term “dust pneumonia” gets thrown around quite often, especially as it relates to young calf respiratory issues.
We hear of human issues with “farmer's lung” or “coal-miners lung”, otherwise known as silicosis. This is a chronic condition that takes many years to develop. Cattle don't live long enough to become afflicted with silicosis; rather, the effect of dust on calves is a bit more immediate.
I've usually been of the mind that dust does not cause pneumonia or respiratory disease by itself. Persistent dusty conditions diminish the effectiveness of the calf's innate respiratory immunity. Innate immunity consists of the features of the body that non-specifically (as opposed to specific features such as antibodies) fight harmful germs. In the respiratory tract, innate immunity includes the moisture of the mucous membranes (traps germs and foreign material), special cells with hairlike projections that line the respiratory passages (sweep germs and foreign material up so they can be coughed out), and macrophages (white blood cells deep in the lung that eat up germs and foreign material).
Dust can “clog up” all of these features of the immune system. Therefore, in dusty conditions, it's more likely that germs such as Mannheimia, Haemophilus, and Mycoplasma will cause clinical illness. These germs can be found in the upper respiratory tract of normal calves, but when a calf's defenses are disrupted, they then can spread to depths of the lungs and result in pneumonia.
What can be done to prevent dust from having an adverse effect on calves? Above-normal precipitation would help! In the meantime, producers have been trying to reduce dust where they can by wetting down pen floors. This does not help much in pasture situations, of course.
Because dust problems result in illness due to all the regular respiratory pathogens, a well-thought out vaccination program prior to weaning will help. Early recognition of sick calves and prompt treatment with an antibiotic recommended by a veterinarian is also key. Many of these cases will respond to these treatments.
South Dakota State University, in conjunction with three other land-grant institutions, is involved in a project seeking to characterize risk factors of pre-weaning calf pneumonia. If you have experienced these cases in your herd, we would be interested in having you participate. Please contact me at SDSU, or your local veterinarian.
Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.
