Interpretation of the results emphasized the importance of microbiological culture and antimicrobial susceptibility testing in foals with pneumonia caused by R equi.

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Genetic introgression, especially from interspecies hybridization, is a significant threat to species conservation worldwide. In this study, 11 US federal bison populations were comprehensively examined for evidence of both mitochondrial and nuclear domestic cattle (Bos taurus) introgression. Mitochondrial introgression was examined using established polymerase chain reaction methods and confirmed through analysis of D-loop sequences. Nuclear introgression was assessed in 14 chromosomal regions through examination of microsatellite electromorph and sequence differences between bison and domestic cattle. Only one population was identified with domestic cattle mitochondrial DNA introgression. In contrast, evidence of nuclear introgression was found in 7 (63.6%) of the examined populations. Historic accounts of bison transfers among populations were corroborated with evidence of introgressed DNA transmission. While neither nuclear nor mitochondrial domestic cattle introgression was detected in bison from Grand Teton National Park, Sully's Hill National Game Preserve, Wind Cave National Park, or Yellowstone National Park, adequate sample sizes were available only from the last 2 populations to allow for statistical confidence (>90%) in nuclear introgression detection limits. The identification of genetically unique and undisturbed populations is critical to species conservation efforts, and this study serves as a model for the genetic evaluation of interspecies introgression.

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Amino acid replacements encoded by the prion protein gene (PRNP) have been associated with transmissible and hereditary spongiform encephalopathies in mammalian species. However, an association between bovine spongiform encephalopathy (BSE) and bovine PRNP exon 3 has not been detected. Moreover, little is currently known regarding the mechanisms of evolution influencing the bovine PRNP gene. Therefore, in this study we evaluated the patterns of nucleotide variation associated with PRNP exon 3 for 36 breeds of domestic cattle and representative samples for 10 additional species of Bovinae. The results of our study indicate that strong purifying selection has intensely constrained PRNP over the long-term evolutionary history of the subfamily Bovinae, especially in regions considered to be of functional, structural, and pathogenic importance in humans as well as other mammals. The driving force behind this intense level of purifying selection remains to be explained.T ransmissible spongiform encephalopathies, or prion diseases, are inevitably fatal neurodegenerative diseases that occur in humans as well as domestic and wild animals (1-3). Traditionally, human spongiform encephalopathies have been classified into Creutzfeldt-Jakob disease (CJD), GerstmannSträusler-Scheinker disease, and kuru, with more recent classification into variant CJD (1). Animal transmissible spongiform encephalopathies include transmissible mink encephalopathy, scrapie of sheep and goats, chronic wasting disease of deer and elk, feline spongiform encephalopathy, and bovine spongiform encephalopathy (BSE) (1). Central to the development of these diseases is the accumulation of an infectious protease-resistant isoform (PrP Sc ) of the host-encoded cellular prion protein (PrP C ) in tissues of the central nervous system (2-5).The prototypical transmissible spongiform encephalopathy, scrapie, has been observed in European sheep for Ͼ200 years, whereas BSE in domestic cattle (Bos taurus and Bos indicus; hereafter, cattle) dates to 1986, presumably resulting from scrapie-and͞or BSE-infected cattle feed (6-9). Thus, BSE seems to be a more recent phenomenon associated with modern agricultural practices. This idea is supported by several lines of evidence. First, at least 14 amino acid polymorphisms encoded by exon 3 of the ovine prion protein gene (PRNP) have been described (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and those associated with codons 136 and 171 have been shown to influence expression of scrapie (8, 10). However, no amino acid polymorphisms associated with BSE have been identified in cattle, although an insertion-deletion (indel) polymorphism in the putative bovine PRNP promoter was shown to exhibit an association with BSE in a few German cattle breeds (21). Second, recorded patterns of variation within cattle PRNP exon 3 are markedly different from those observed in sheep, with variability in cattle primarily restricted to 11 synonymous nucleotide sites and two nonsynonymous sites where low-frequency variation has been observed (2...