Bluetongue virus is a concern for both livestock and wildlife, and in particular, sheep and pronghorn in Wyoming. However, not much is known about the economics of vaccinating sheep against this episodic disease. Wyoming researchers recently published a paper in the journal Frontiers in Veterinary Science using budget and stochastic modeling scenarios. This modeling approach takes into account the variation of disease severity (some years it is a problem and some years it is not a problem) and lamb prices, and the uncertainty of when an outbreak might occur. The models look at 5, 10, 20, and 50 year scenarios and assumed a cost of “$0.32 per dose for modified-live and an estimated price of $1.20 per dose for KV (killed virus)”. The authors concluded “our results show an economically consequential tradeoff between a KV vaccine’s relative safety and higher cost. Unless the purchase price is reduced below our assumed $1.20 per dose, producer adoption of a KV vaccine for BT is likely to be low in the study area. This tradeoff between cost and safety should be considered when policymakers regulate commercial use of the two vaccine types.”
Researchers have been studying the interaction between fire and grazing in wetter ecosystems such as tallgrass prairies and savannahs for a few decades but understanding this interaction in arid and semi-arid ecosystems has not been well quantified until recently. Scientists from the University of Montana recently published a paper in the journal Rangeland Ecology and Management assessing the drivers and feedbacks of cattle selection relative to burned and unburned areas by measuring the strength of selection, plant biomass, crude protein, and vegetation structure/composition. The authors found that cattle preferred grazing in recently burned areas and that as the time since burn elapsed the preference faded. The reason cattle preferred these areas was a significantly higher crude protein level in burned areas compared to unburned areas. This higher crude protein level lasted about 120 days after the fire.
The effects of horse grazing in the riparian areas within the semi-arid and arid sagebrush steppe ecosystem has continued to be an issue of concern and federal scientists recently published a new paper in the journal Rangeland Ecology and Management. This study used exclosures in the Sheldon National Wildlife Refuge in northwestern Nevada from 2008 to 2013. Plots grazed by horses had 7x more bare ground, 60% less litter cover, and a basal cover index that was 65% higher. Density of rushes seemed to increase with grazing but density of sedges did not appear to change. Herbaceous stubble height decreased by up to 80% and visual obstruction of the vegetation by ~70%. The authors concluded that “greater vertical structure in excluded plots could improve hiding and nesting habitat for some riparian-associated wildlife species. Additionally, decreased bare ground with grazing exclusion could reduce erosion potential and susceptibility to invasive plant species.”.
Researchers continue to investigate different formulations and deployment techniques for chemical contraception for feral horses to curb population growth rates. Recently, federal scientists published a study in the Wildlife Society Bulletin assessing the effectiveness of SpayVac® contraception. SpayVac® is an immunocontraceptive that has both PZP and an adjuvant. This study assessed captive BLM horses over a 3 year period following a single treatment with 30 mares in 3 treatment groups (untreated, nonaqueous treatment, aqueous treatment).
Untreated horses had annual fertility rates of 96.7% to 100%. In a treated group (nonaqueous treatment), annual fertility rates were 16.7% in year 1, 75.9% in year 2, and no assessment was made in year 3. In the other treated group (aqueous treatment), annual fertility rates were 13.3% in year 1, 46.7% in year 2, and 43.3% in year 3. Half of the mares in the aquueous group were infertile all 3 years. The authors conclude that “Additional research to explore relationships between vaccine dose, adjuvant, and efficacy is warranted.”
Check it out: http://onlinelibrary.wiley.com/doi/10.1002/wsb.729/full
The interaction between feral horses and native wildlife in the United States is an escalating concern. Scientists recently published a study in the Journal of Arid Environments based on sampling conducted in 2011 and 2012 in Nevada. This study used 22 remote cameras that provided information to select 3 field observation sites for additional sampling. The authors found that when feral horses were around water, pronghorn would spend less time foraging or drinking and more time being vigilant. In nearly 40% of the documented pronghorn*horse interactions, the pronghorn were excluded completely from the water source. The authors did report that direct aggression of the horses was rare, but that the interference of horse presence alone was disrupting pronghorn behavior. The authors conclude that “These effects could have detrimental impacts on pronghorn fitness and population dynamics, particularly under adverse conditions when surface water availability is limited and monopolized by horses.”