HEALTH EVALUATION OF A PRONGHORN ANTELOPE POPULATION IN OREGON

During 1996 and 1997, the U.S. Fish and Wildlife Service conducted a study to determine the cause(s) of population decline and low survival of pronghorn antelope (Antilocapra americana) fawns on Hart Mountain National Antelope Refuge (HMNAR) located in southeastern Oregon (USA). As part of that study, blood, fecal, and tissue samples from 104 neonatal fawns, 40 adult does, and nine adult male pronghorns were collected to conduct a health evaluation of the population. Physiological parameters related to nutrition and/or disease were studied. No abnormalities were found in the complete blood cell counts of adults (n = 40) or fawns (n = 44 to 67). Serum total protein and blood urea nitrogen (BUN) levels were lower compared to other pronghorn populations. Does had mean BUN values significantly lower (P < 0.001) in December 1996 than March 1997. Serum copper (Cu) levels in does (range 0.39 to 0.74 ppm) were considered marginal when compared to domestic animals and other wild ungulates. Fawns had low (0.28 ppm) Cu levels at birth and reached the does' marginal values in about 3 days. Whole blood, serum and liver selenium (Se) levels were considered marginal to low in most segments of the pronghorn population. However, serum levels of vitamin E (range 1.98 to 3.27 μg/ml), as determined from the does captured in March, were apparently sufficient to offset any signs of Se deficiency. No clinical signs of Cu or Se deficiency were observed. Fifty-five of 87 dead fawns were necropsied. Trauma, due to predation by coyotes (Canis latrans), accounted for 62% of the mortality during mid-May to mid-July of each year. Other causes included predation by golden eagles (Aquila chrysaetos) (4%), dystocia (2%), septicemic pasteurellosis (4%), starvation (5%), and unknown (23%). Adult females were tested for serum neutralizing antibodies to Brucella spp. (n = 20, negative), Leptospira interrogans (n = 20, negative), bluetongue virus (n = 20, 35% positive), epizootic hemorrhagic disease virus (n = 20, 30% positive), respiratory syncytial virus (n = 18, negative), parainfluenza virus type 3 (n = 18, 67% positive), infectious bovine rhinotracheitis (n = 18, negative), and bovine viral diarrhea (n = 18, negative). Considering the parameters examined, we found no apparent predisposing factors to mortality including those killed by coyotes, but some nutritional parameters suggest that pronghorns on HMNAR exist on a diet low in protein and Se and marginal in Cu. The effect these factors have on the population is not known.