Horn flies on a beef cow
Indigenous tribes of North America, Africa and Australia used fire for a variety of reasons including control of insects. Commercial livestock operators have typically not recognized the impact of fire in reducing parasites on animals. While the impact of fire on external parasites such as ticks has been documented, there has been little attention paid to how fire could be used to manage fly pests of cattle. Horn flies are an external parasite of cattle that cause over $1 billion in economic losses each year. Cattle serve as hosts for horn flies by providing blood meals and fecal pats that are used for laying eggs and overwintering pupa. Given the fire prone ecosystems of North America, range scientists and livestock entomologists are evaluating the response of horn flies (a non-native pest from Eurasia) to fires. The current trend in managing horn flies is with insecticides that are fed, sprayed or impregnated in ear tags. Resistance to chemical active ingredients is a major problem and is now widespread.
In 2011, cattle in Oklahoma and Iowa were evaluated for horn fly numbers. Cattle were either on pastures that were patch-burned (a portion of the pasture burned each year) or on pastures that had not been burned in over two years. All fires were conducted in March of that year. Horn flies were counted during periods of peak activity and data was evaluated for location and treatment effects. Cattle on pastures that were patch-burned had 41% fewer horn flies than cattle on pastures that had not been burned. The accepted economic threshold for treatment of horns flies is 200 flies per cow, with 300 flies per cow causing behavioral stress. The unburned pastures had >400 horn flies per cow, while the patch burn pasture cows had approximately half as many horn flies. It is thought that the application of fire is effective by two primary mechanisms: (1) cattle spend more time in the recently burned patch than unburned patches (as they are attracted to the highly palatable and nutritious plant regrowth after fire) and (2) fire in the dormant season (late winter and early spring) alters cow pats when pupa are overwintering in or below them.
Benefits of Fire Relative to Parasites
Using fire to manage horn flies is anticipated to have a number of positive impacts, including: (1) reducing horn fly numbers is expected to result in a reduction of stress annoyance behaviors such as twitching, head throwing and swishing of the tail and ultimately an increase in grazing time, (2) reducing horn flies has been documented in numerous studies to have a positive impact on cattle performance, (3) the potential impact of fire on any parasite of cattle is an exciting alternative to the use of pesticides and a potential strategy to avoid the development of resistance to chemical treatments, (4) fly pests of cattle have been documented to vector diseases (horn flies are suspected of transmitting anaplasmosis and face flies are suspected of transmitting pinkeye). Lastly, fire provides other benefits to pasture such as slowing woody plant encroachment and removing dormant plant litter and allowing for lush regrowth of grass.
Importance of Fire
Fire is an important driver of many North American ecosystems, particularly grasslands. The influence of fire on the plant community is largely attributed to its removal of dead standing plant material, impact on forage quality, and the impact on grazing animals. Cattle production in undisturbed tallgrass prairie can be low due to the accumulation of dead standing plant material. However, fire can increase production over 75%. Historically, large bison herds followed fire as they were attracted to the lush regrowth that emerged. Today, managers use prescribed burning to capitalize on this change in forage quality for cattle production.
Forage quality is typically expressed as crude protein (CP) which is based on the nitrogen content of forage. This nitrogen content is critical for microorganisms in the rumen. Other measures of forage quality include palatability (typically associated with texture and moisture content) and digestibility (largely based on fiber and lignin). The primary influence of fire on forage quality is the removal of standing, dormant plant material. Forage quality is largely a function of time: as plants age (mature) they decrease in quality. This decrease in quality is due to the increase in fiber and lignin content, resulting in reduced digestibility and animal consumption. Prescribed fire remove dormant plant material, increasing the nutrition and digestibility of post-fire regrowth. While prescribed fires are commonly conducted during the late winter or early spring, growing season (summer) fires have the same effect and can boost forage quality during a period of the year where it is typically decreasing. Furthermore, the interaction of fire and grazing will impact below ground plant growth by increasing nitrogen mineralization and plant nitrogen availability, and improving the root tissue quality.
Benefits of Higher Forage Quality
Forage quality is a critical component of cattle production including reproductive efficiency, rebreeding, calf production, animal growth and milk production. Understanding the importance of fire to native rangeland plants and the potential benefits to cattle can be a useful tool for ranch managers.
Achieving optimum livestock production on rangelands many times can conflict with wildlife conservation strategies that require lower stocking rates to maintain suitable habitat. Traditionally, livestock producers try to maximize gain per-acre by uniformly managing vegetation in pastures. Often this is achieved either by heavily grazing, burning the entire pasture, or both. This management strategy can create suitable habitat for some wildlife species, but poor quality habitat for others.
Combining the spatial and temporal interaction of fire and grazing (patch-burning) a conservation-based approach to land management can be achieved. This practice can increase rangeland biodiversity by creating heterogeneous vegetation structure and composition that is beneficial to multiple wildlife species. However, for conservation strategies to be successfully implemented, they need to be both effective and economically sustainable. In both mixed-grass prairie and tallgrass prairie, cattle weight gain was compared in pastures with traditional fire and grazing management (continuous grazing, with periodic fire on tallgrass prairie and seasonal grazing without fire on mixed-grass prairie) and conservation based management (pyric-herbivory applied through patch burning), both at a moderate stocking rate. Stocker cattle weight gain, calf weight gain, and cow body condition score were comparable between the traditional and conservation based management at the tallgrass prairie site for the duration of the eight-year study, indicating that conservation management doesn’t decrease livestock production or profitability.
In the mixed-grass prairie pastures, stocker cattle gain was not different between traditional and conservation management for the first four years. However, stocker cattle in conservation based management out gained cattle in traditional management beginning in year five and remained 27% greater for the next six years of the study. Moreover, cattle weight gain under conservation management varied less year to year making profitability more consistent. Traditional management in mixed-grass prairie did not include fire, the process that improved range conditions and likely was associated with increased stocker cattle performance under conservation management. In conclusion, pyric-herbivory is a conservation-based rangeland management strategy that returns fire to the landscape without reduced stocking rate, deferment, or rest.
Figure 1. Cattle weight gain on traditionally managed and patch-burn managed tallgrass prairie.
Figure 2. Cattle weight gain on traditionally managed and patch-burn managed mixed-grass prairie. An * indicates years when patch-burned managed cattle gained more than traditionally managed cattle.
Troublesome pests such as ticks can be controlled with fire. However, for most parasites, control by fire lasts only for one growing season post-burn.
Many tourism areas suffer economic loss because of the public’s perception of ticks and other pests in parks, campgrounds, and other recreational facilities. Ticks pose a serious health risk to humans, pets, livestock, and wildlife because of the diseases they can carry. Rocky Mountain spotted fever, Lyme’s disease, and other infections can be transmitted to humans from ticks. Domestic animals can also contract fatal diseases from ticks. Decreased livestock production from insect borne illnesses can also cost livestock producers thousands of dollars each year.
Controlling Ticks With Patch-Burning
Current research suggests patch-burning (patch-burn grazing) significantly reduces ticks on domestic livestock. When a patch is burned, the livestock follow the fresh burned areas and camp out on those areas until another patch is burned. Burning the patch kills the ticks, removes their habitat, and limits the livestock’s contact with ticks because they are concentrated on the burned area. Since the livestock follow the burns, they remain in areas with fewer ticks.