No abstract

It is suggested that for alpacas in southern Australia a subcutaneous dose of 1000 IU D3/kg body weight to crias in late autumn and again in mid winter and to adult females in mid winter should prevent vitamin D inadequacy.

Comparisons have been made of [6_ 3H]-, [3-3H]-, and [2-3H]glucose with [U-14C]glucose for measuring parameters of glucose metabolism in sheep given their daily ration in 24 equal amounts at hourly intervals. The specific radioactivity (R) of plasma glucose was measured at frequent intervals from 0 to 10 hr and 0 to 32 hr after the start of a constant infusion. or single injection, of mixtures of these isotopes respectively.Estimates of glucose pool size by consideration of either the initial rectilinear slope (monoexponential analysis) or the multiexponential components of the log R-time curve after single injections of [3H} and [14C]glucose were similar.The mean irreversible loss of plasma glucose estimated by using [3-3H}, and [2-3H]glucose was approximately 79, 70, and 103 respectively. Further release of tritium to body water apparently occurred between 7 and 32 hr following injections of [6-3H} and [3-3H]glucose.Resynthesis of glucose from blood bicarbonate was equivalent to approximately 2% of the irreversible loss of glucose carbon, whereas resynthesis of carbonbound hydrogen of plasma glucose from body water was negligible, although about 91 % of this hydrogen was apparently derived from body water.It was suggested that 20-30% of the intermediates of glucose metabolism were utilized in synthetic reactions and that [2-3H]glucose with [U-14C]glucose was the most useful mixture of labelled glucoses for studies of glucose metabolism, particularly for estimating the extent of glucose resynthesis.

I . Short-term effects of infusions of propionate, amino acids and butyrate on gluconeogenesis, as indicated by changes in the irreversible loss of plasma glucose, synthesis of glucose from ruminal propionate or fixation of blood bicarbonate into glucose have been examined in sheep given their daily ration in twenty-four equal portions at hourly intervals.2. Sheep received intravenous infusions of [6-SH]glucose usually in combination with [U-14C]glucose or NaHI4CO, or with intraruminal infusions of [~-~~C]propionate. Substrates were infused over a 3-7 h period and followed estimates of pre-infusion kinetic measurements.3. It was demonstrated that intraruminal and intramesenteric vein infusions of sodium propionate and intra-abomasal infusions of casein liydrolysate stimulated gluconeogenesis. Glucose synthesis showed a linear response to the infusion of these substrates, which varied from 0.35-6.35 mmol propionate/min and 50-160 nig casein/min. 4.The increment in the measured production rate of propionate in the rumen was consistcntly less than the rate of addition of propionate to the rumen.5. Intramesenteric vein infusions of sodium butyrate at successive rates of 0.25 and 0.50 mmol/min produced only an initial transient increase in plasma glucose production. Since the rate of glucose synthesis from ruminal propionate was not altered, it was suggested that butyrate initiated glycogen mobilization.

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