Browsing by Subject "Johne's Disease"
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Item Diversity and Evolution of the Bovine and Equine Toll-Like Receptor Gene Family: Applications to Animal Disease(2012-08-20) Fisher, Colleen 1988-Genes modulating innate immunity in mammals are generally considered the first line of defense with respect to invading pathogens and therefore it has become important to characterize naturally occurring genetic variation, and subsequently determine whether this variation is likely to be benign, beneficial, or detrimental to the host. Relevant to this study, the mammalian Toll-like receptor proteins (TLR), encoded by members of the TLR gene family, have the capacity to recognize a wide variety of pathogen ligands, and mutations within these genes have been shown to influence disease susceptibility or resistance within mammalian species. Two studies which sought to determine the frequency and distribution of naturally occurring genetic variation within the bovine and equine TLR genes revealed a large number of discrete point mutations, which were subsequently used to reconstruct haplotypes for each investigated gene across a large number of samples. Detailed analyses of haplotypes provided evidence for extensive haplotype sharing among specialized breeds, subspecies, and even divergent species. Classical and new tests of selection provided evidence for significant deviations from a strictly neutral model of molecular evolution for both cattle as well as equids, with some of the same TLR genes deviating from a strictly neutral model among divergent species. As a first step toward determining whether naturally occurring bovine TLR variation is likely to be benign, beneficial, or detrimental, we tested validated variation from bovine TLR genes capable of recognizing components of Mycobacteria for associations with Mycobacterium avium subspecies paratuberculosis (MAP) infection in dairy cattle, and found several SNPs that were nominally associated with disease status, thereby providing evidence for small-effect loci potentially influencing risk for differential susceptibility to Johne's disease.Item Economic Consequences Associated with Johne?s Disease in Cow-Calf Operations(2013-08-05) Bhattarai, BikashJohne?s disease (JD) in cattle is a disease of economic importance caused by Mycobacterium avium subspecies paratuberculosis (MAP). Studies were conducted to estimate the losses due to lower weaning weight of beef calves from MAP test-positive dams, to compare the perceptions of producers and veterinarians on the burden and economic aspects of MAP infection in cow-calf herds, and to evaluate whether testing and culling MAP test-positive cows is economically beneficial. Calves from cows with strong-positive ELISA results were 21.5 kg lighter at weaning compared to calves from ELISA-negative cows. Calves from heavy MAP shedding cows were 58.5 kg lighter, and calves from moderate shedders were 40.8 kg lighter compared to the calves from fecal-culture negative cows. Based on average feeder calf value during 2007 to 2012, these losses corresponded to US $57 per calf for ELISA strong-positive dams, US $157 per calf for heavy fecal shedder dams, and US $109 per calf for a moderate fecal shedder dam. Seedstock producers and the producers enrolled in control programs were more likely to have MAP uninfected herds. The average prevalence reported by producers was 0.8%. Compared to the small herds (<50 head), the average test-positive percentages and estimated prevalences were reported to be higher in medium (50-149) and highest in large (?150) herds. Veterinarians reported an overall animal level prevalence in their client herds of 5%. Seedstock herds had a lower prevalence and these producers were more likely to enroll in a JD control program. Income lost due to the presence of JD in an infected cattle herd was perceived to be higher by veterinarians. Compared to the veterinarians, seedstock producers were more likely to perceive genetic losses due to culling MAP positive cows. Average annual loss due to JD in a 100 cow herd with a 7% MAP prevalence was $1,644 and $1,747 based on information provided by producers and veterinarians, respectively. Herd level production decreased with increasing prevalence. Compared to test and cull after ELISA or ELISA followed by fecal culture, using fecal culture alone provided the fastest reduction in herd prevalence. Fecal culture was also the least costly alternative based on long-term cumulative costs of an annual test and cull program. Results from the current study suggest that although testing provides faster progress, limiting within herd transmission by sale of all weaned calves and purchasing only low-risk replacements can also reduce prevalence. Results suggest that MAP infection in cows causes significant losses for the calves that are produced. While the knowledge about JD varied between producers and veterinarians, seedstock producers were more enthusiastic about MAP control programs and had lower MAP prevalence in their herds. Overall losses due to MAP infection in the herd might be substantial. It is very costly to control or eliminate MAP once the infection is established in a herd.