Livestock producers' views on accessing food-animal veterinary services: implications for student recruitment, training, and practice management.

Nationally, shortages of food-animal veterinary practitioners have been projected over the next several years. The purpose of this study was to ascertain livestock producers' perceptions on access to veterinary services and to measure opinions on potential solutions to access problems. Data for the study were from a 2006 survey of livestock producers in Tennessee. The study found that the majority of livestock producers had not perceived problems in obtaining veterinary services during the past year. Among those who had, the problems most commonly cited were a delay in obtaining services; that the veterinarian would treat the animal only if the producer transported it to the veterinary facility; and that the cost of the veterinary service was too high relative to the value of the animal. While it was hypothesized that producers who experienced a problem would have smaller farms on average and would reside in counties with lower numbers of large- or food-animal veterinarians, the results did not support this hypothesis. Among those who perceived a problem, scholarship programs to encourage veterinary students to specialize in large- or food-animal care and greater availability of veterinary technicians to perform health care services were viewed as effective ways to alleviate access problems. Financial incentives for veterinarians to locate in rural areas were also viewed as effective. While shortages have been predicted nationally, data from this survey do not suggest a perceived shortage in Tennessee. Problems in obtaining services appear to be more closely related to practice management and availability of large-animal practitioners in dairy and equine medicine.

Changes in antibiotic susceptability of Escherichia coli isolated from steers exposed to antibiotics during the early feeding period.

The influence of therapeutic choices on antibiotic resistance of intestinal bacteria may have food safety consequences. Changes in antibiotic susceptibility of Escherichia coli to antibiotics currently approved for prevention and treatment of bovine respiratory disease were evaluated in 260 feedlot steers. Susceptibilities to antimicrobial compounds were compared among three treatment groups at three times between arrival at the feedlot and harvest to assess changes over the course of the feeding period. No significant change was found in the resistance of E. coli to tilmicosin, florfenicol, and enrofloxacin, which were used to prevent and treat respiratory disease in this study. Despite an absence of exposure to ampicillin and ceftiofur, a significant increase in resistance was observed for these two antimicrobial drugs that declined by the end of the feeding period. In this study, use of approved antimicrobials early in the feeding period for the prevention and treatment of bovine respiratory disease had little effect on antimicrobial resistance of E. coli isolated from cattle near the time of slaughter.

Influence of extracellular matrix on bovine mammary gland progenitor cell growth and differentiation.

OBJECTIVE: To examine the impact of simple versus complex extracellular matrices (ECMs) on morphologic development and differentiation of bovine mammary gland progenitor cells (BMGPCs). SAMPLE POPULATION: Cultures of BMGPCs. PROCEDURES: BMGPCs were grown on the following extracellular matrices: collagen I, collagen IV, laminin, and a commercially available gelatinous protein mixture. Cells were examined with light microscopy and transmission electron microscopy. RESULTS: Formation of organoids and production of the gap junction protein, connexin 43, were the criteria for BMGPC differentiation. The BMGPCs formed a 2-dimensional monolayer when grown on plastic, laminin, collagen I, or collagen IV. These cells did not have a network of cells forming epithelial organoids resembling a honeycomb. However, they did produce gap junction proteins. When BMGPCs were cultured on the commercially available gelatinous protein mixture, 3-dimensional epithelial organoids resembling a honeycomb formed and connexin 43 was produced. The thickness of the commercially available gelatinous protein mixture also regulated cell shape reorganization. Cell density affected the formation organoid networks and the rate at which monolayers reached confluency. CONCLUSIONS AND CLINICAL RELEVANCE: When plated on a commercially available gelatinous protein mixture, the BMGPC culture system allowed us to simulate, in vitro, the interaction between epithelial cells in varying stages of differentiation and the microenvironment. Thus, a heterogeneous ECM, such as the commercially available gelatinous protein mixture, is more physiologically relevant in providing a microenvironment for BMGPC lineage pathway differentiation to mimic an in vivo environment. In contrast, BMGPCs grown on homogenous ECM, although able to produce connexin 43, are unable to form organoids.

Caspase activation in equine influenza virus induced apoptotic cell death.

Equine influenza virus (EIV) is the leading cause of acute respiratory infection in horses worldwide. In recent years, the precise mechanism by which influenza infection kills host cells is being re-evaluated. In this report, we examined whether caspases, a group of intracellular proteases, are activated following EIV infection and contribute to EIV-mediated cell death. Western blotting analysis indicated that a nuclear target of caspase-3, poly(ADP-ribose) polymerase (PARP) was proteolytically cleaved in EIV-infected MDCK cells, but not in mock-infected cells. In comparison with caspase-3 specific inhibitor Ac-DEVD-CHO, a general caspase inhibitor Boc-D-FMK provided much stronger inhibition of EIV-induced cytopathic effect and apoptosis. Our results suggest that EIV may activate more than one caspase. Caspase activation and cleavage of its cellular targets may play a critical role in EIV-mediated cytotoxicity.

Isolation and differentiation of bovine mammary gland progenitor cell populations.

OBJECTIVE: To isolate bovine mammary gland cells with stem cell characteristics. SAMPLE POPULATION: Monolayers of bovine mammary gland cells. PROCEDURE: Mammary gland cell populations were separated by use of selected media supplements. Phenotypic characteristics were examined via light and transmission electron microscopy. Cellular expression of casein and connexin 43 was identified immunohistochemically. A scrape-loading and dye transfer assay was used to examine the mammary gland cell populations for homogenous gap junctional intercellular communication (GJIC). RESULTS: Subpopulations of mammary gland cells grown in vitro are classified on the basis of their distinct morphologic features and ability to communicate via gap junctions. Ultrastructurally, 2 morphologically distinct cell types were classified as type I and II cells. Type I cells were small light undiffertiated cells and large light undifferentiated cells that were deficient in functional gap junctions (as is characteristic of stem cells). Type II cells included large light differentiated cells and terminally differentiated cells; GJIC was functional in type II cells. Type II cells had cytoplasmic expression of connexin 43, whereas, type I cells did not. All cells expressed casein. CONCLUSIONS AND CLINICAL RELEVANCE: Subpopulations of bovine mammary gland cells with stem cell characteristics were identified. Phenotypic differences are observed among type I bovine mammary gland cells with stem cell characteristics. Gap junctional intercellular communication may be necessary for the differentiation of stem cells. Characterization of bovine mammary gland stem cells and their progeny may provide a new tool with which to study mammary gland health.

Infectivity of equine H3N8 influenza virus in bovine cells and calves.

BACKGROUND: Serological evidence for influenza A, subtype H1 and H3 virus infections of bovines, associated with respiratory disease and decreased milk production, has been reported. Equine H3N8 influenza virus circulates widely and was responsible for the introduction of H3N8 influenza into canines. OBJECTIVE: To explore the possibility that equine H3N8 influenza might also infect bovines. METHODS: To assess the incidence of seroconversion in the field, a retrospective survey of bovine serum samples was carried out. Also, primary cultures of bovine nasal turbinate cells, and live beef calves, were studied for their permissiveness to infection. RESULTS AND CONCLUSIONS: We found serological evidence of exposure of bovines in Kentucky to H3 influenza. We demonstrate that cultured bovine respiratory epithelium is permissive for the growth of equine H3N8 influenza virus in vitro, but this virus does not replicate extensively or produce disease in experimentally inoculated cattle.

Genetic diversity of Cryptosporidium spp. in cattle in Michigan: implications for understanding the transmission dynamics.

Epidemiological and molecular data on 248 bovine, 17 human, and 16 water samples of Cryptosporidium spp. collected from the lower peninsula of Michigan between 1997 and 2000 were analysed. Cryptosporidium parvum bovine genotype and Cryptosporidium andersoni were found in 56 and four cattle samples, respectively. A total of six C. parvum subgenotypes were found in 34 bovine samples, and five of the eight farms had two or three subgenotypes in cattle. Six water samples from these farms had C. andersoni, five had the C. parvum bovine genotype, and one had Cryptosporidium muris. In contrast, four PCR-positive human samples produced the C. parvum bovine genotype and two had the C. parvum human genotype. Among the C. parvum bovine genotype samples, two human samples and one water sample had subgenotypes identical to those found on cattle farms. The results of this study demonstrate the potential use of molecular methods in tracking the transmission of Cryptosporidium.