I. Glucose entry rates into the blood and propionate production rates in the rumen have been measured in sheep given rations containing varying proportions of starch and roughage (lucerne).2. Glucose entry rates and propionate production rates were similar for all rations studied. 3. The proportion of the glucose entry rate arising from propionate produced in the rumen was highest on the ration containing the greatest quantity of lucerne and decreased as the proportion of starch in the ration increased. Rate of conversion of propionate into glucose was estimated and was found to decrease as the amount of starch in the ration increased.4. Concentrations of total volatile fatty acids (VFA) in the ruminal fluid were lowest in the ration with the greatest proportion of starch, implying lower VFA production rates with the starch rations although intakes of digestible energy were approximately the same. The mean concentrations and rates of production of propionate in ruminal fluid were similar for all rations. 5 . The low VFA concentrations and the reduced conversion of propionate into glucose on the high rations, despite similar propionate production rates and glucose entry rates, may have been due to starch escaping ruminal fermentation. I t is suggested that this glucose absorption may have reduced gluconeogenesis from propionate.In ruminants, gluconeogenesis is a major biosynthetic process, since apparently only in animals given a high proportion of starch in their diets could there be significant absorption of glucose from the alimentary tract (MacRae & Armstrong, 1966; Lindsay, 1959; Armstrong, 1965). Estimates of glucose entry rates in non-pregnant sheep have varied from 1.4 to 4 3 mg/kg per min (Annison & White, 1961 ;Kronfeld & Simesen, 1961;Bergman, 1963; Ford, 1963 Ford, , 1965Bergman, Roe & Kon, 1966;Leng, Steel & Luick, 1967). The variations in estimates may be in part attributed to differences in the feeding regime and in the techniques adopted in the various laboratories. For instance, in most studies animals were fed once or twice daily and entry rates were estimated some time after the animal had eaten; this usually coincided with maximum volatile fatty acid (VFA) concentration in the rumen. Ford (1965) has shown that glucose entry rate in sheep varied with the quantity and quality of food eaten and he suggested that there was an increase in gluconeogenesis as feed intake increased.In sheep given lucerne at hourly intervals, propionate produced in the rumen contributed 54 % of the carbon of the glucose synthesized (Leng et al. 1967), whereas it was shown by Bergman et al. (1966) that absorbed propionate contributed 27 yo of the glucose entry rate. As only a relatively small proportion of the propionate produced in the rumen was converted into glucose, it appeared that on the diets of lucerne

Rubber tires contain several compounds that are known or suspected carcinogens.  Many carcinogens are mutagens, and fluctuation assays based on the Ames test can be used as an initial screen for mutagenic potential.  Granulated crumb rubber from recycled tires is commonly used in the creation of artificial athletic fields, and the surface temperature of these fields can reach levels far above the ambient temperature.  In this study, crumb rubber samples taken directly from four separate artificial athletic field surfaces were used to make leachates using water at different temperatures.  For each of these fields, leachates obtained in water at 70 ºC showed significant mutagenic potential (p ≤ .001) in Salmonella typhimurium fluctuation assays.  Leachates obtained in water at 40 ºC showed no mutagenic potential for any of the fields tested.  For one field, crumb rubber heated in water at temperatures as low as 50 ºC resulted in significant mutagenic potential (p ≤ 0.001).  Water used in an experiment designed to mimic the irrigation of an artificial athletic field also showed mutagenic potential (p ≤ 0.001) in a fluctuation assay.  These results suggest that at the higher temperatures that can exist on artificial athletic field surfaces, the crumb rubber infill on these artificial athletic fields can become the source of a water soluble agent with mutagenic potential in bacteria.

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