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Escherichia coli O157:H7 were cultured in the presence of norepinephrine to generate conditioned media. The presence of a growth-inducing factor(s) in the conditioned media was examined by measurements of the ability of conditioned media to support the growth of fresh cultures of E coli O157:H7. Supplementation of fresh cultures with as little as 0.024% (v/v) norepinephrine conditioned medium resulted in increased growth as compared to controls, thereby indicating the presence of an autoinducer of growth. Analysis of the production kinetics for the autoinducer during the generation of conditioned media indicates that it differs from other more well characterized autoinducers. It is proposed that the neurohumoral environment of the host may contribute to the production of bacterial growth factors.

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Larkspurs (Delphinium spp.) are native forbs that are poisonous to cattle and cost livestock producers millions of dollars in losses each year. Macro and micro minerals are required for normal functioning of essentially all metabolic processes in ruminants. The role that mineral status may play in larkspur poisoning in cattle is not clear. In this study, we seek to determine the effects a mineral-salt supplement, commonly used by cattle producers, to potentially reduce cattle losses to larkspur. The ability of mineral-salt supplementation to alter susceptibility to larkspur toxicosis was evaluated in a pen study. Animals supplemented with mineral-salt were found to be less susceptible to larkspur poisoning than the non-supplemented animals. A separate group of animals were then grazed on larkspur infested rangelands. One group was supplemented with a mineral-salt mix and the other group did not receive any mineral-salt. Supplementing cattle with the mineral-salt mix did not alter larkspur consumption (P > 0.05). However, overall larkspur consumption was low and averaged 3 ± 1.0% and 2 ± 1.1% for cattle supplemented with mineral and non-supplemented, respectively. Serum was collected from animals once a week during the grazing study. Average and maximum serum concentrations of toxic larkspur alkaloids were numerically higher in mineral-salt supplemented cattle compared with the non-supplemented animals. Results from the pen study suggest that a good mineral supplementation program will provide a protective effect for animals grazing in larkspur-infested ranges. The mineral-salt supplemented steers, in the grazing study, were not observed to consume less larkspur than the non-supplemented animals; however, the mineral-salt supplemented animals had higher concentrations of larkspur alkaloids in their serum indicating they may be able to tolerate higher larkspur consumption. The data also indicate that mineral-salt supplementation must be continuous throughout the time the animals are grazing these rangelands as the positive effects can be lost within 30 d post supplementation.