One of our leading hypotheses regarding the decline of pronghorn populations includes the presence of diseases or parasites. During a pronghorn die-off in the summer of 2009, we identified unprecedented parasite loads from several pronghorn that we were able to necropsy. Barber pole worms (Haemonchus spp.) are parasitic roundworms that attach to the inner lining of the digestive system and an average adult worm is able to draw off 0.1 cc of blood/day. Additionally, where the worms attach in the stomach becomes scarified inhibiting the ability of the stomach to absorb nutrients. Parasite loads of 2,000 for an individual sheep or goat would jeopardize their survival. To better understand the role diseases and parasites have in pronghorn survival, we initiated a thorough investigation.

In the fall of 2009, 2010, and 2011 we collected samples of hunter-harvested pronghorn to evaluate parasite loads, as well as the occurrence of blue tongue, epizootic hemorrhagic disease, and copper and selenium levels. We obtained 102, 95, and 41 pronghorn samples in 2009, 2010, and 2011, respectively. Over 95% of the pronghorn evaluated in our study had Haemonchus in their abomasum. Some parasite loads exceeded 4,000 individual worms. The herd units in the Marfa Plateau had the highest parasite loads in the Trans-Pecos; they also had the lowest fawn production during this time. Comparing all pronghorn, average parasite loads were highest in 2009 (552 worms/abomasum) compared to 2010 (268) and 2011 (461).

During our study we were also able to establish a noninvasive technique for evaluating parasite loads—fecal egg counts. From our data, fecal egg counts are highly correlated to abomasum parasite load (92%) thus allowing us to monitor parasite loads without sacrificing pronghorn. This technique is especially important as we begin evaluating parasite loads of pronghorn herds for potential restoration efforts.

Although Haemonchus have been documented in pronghorn prior to our findings, infestations of this magnitude have not been reported previously. The high levels of parasites can have detrimental impacts on pronghorn survival. Infested pronghorn can become anemic and weak making them more susceptible to predation and other mortality factors. Most recently, our collaborators suggest that the strain of Haemonchus does not appear to be from livestock and that it may be a new strain specific to pronghorn, desert environments, or both.