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Biomedical subjects

A C Field

Publications and source records attributed to A C Field.

At least 37 records · Page 2Linked to original sources
PubMed1982

A model for zinc metabolism in sheep given a diet of hay.

1. Four pairs of Scottish Blackface ewes were given a basal diet of hay, providing 8 mg zinc/d, and one of four levels of supplementary Zn (0,75, 150 or 225 mg/d) continuously by intraruminal infusion. 2. 65Zn (59 microCi) was given intravenously after stabilization for 14 d and the changes in specific radioactivity (SR) of plasma and faeces were monitored for a further 10 and 13 d respectively. The faecal endogenous losses and absorption of Zn were estimated, using the principle of isotope dilution, by two methods using the whole or latter parts of SR:time curves. 3. Faecal endogenous losses were estimated by the part area method to be 4.9, 6.4, 5.1 and 6.3 +/- 0.35 mg/d at 0, 75, 150 and 225 mg supplemental Zn/d i.e. largely unaffected by Zn intake and averaging 0.11 mg/kg live weight (LW). The whole area method gave similar results. 4. Urinary excretion was negligible (probably less than 0.2 mg/d) for all sheep. 5. The amount of Zn absorbed was assumed to equal the irreversible loss of Zn under steady-state conditions and found to remain constant at 7.6 +/- 0.39 and 10.3 +/- 0.6 mg/d when calculated by "whole' and "part area' methods. Zn retention did not increase with Zn intake and homoeostasis was achieved primarily by control of Zn absorption which fell from 0.75 to 0.03 or from 0.96 to 0.05 of intake, depending on method of calculation, as intakes increased.

Animal Feed↗
PubMed1982

Foetal and maternal rates of urea production and disposal in well-nourished and undernourished sheep.

1. Five monotocous and two ditocous Scottish Blackface ewes with indwelling catheters in an umbilical artery and vein of one foetus only and in both maternal jugular veins were used. 2. Experiments were conducted over a period of 2 d when [14C]urea was infused intravenously over 9 h into either the mother or foetus, separate days being used for each infusion. Two series of experiments were completed, one in well-nourished and the other in undernourished sheep at 125-141 and 138-143 d of gestation respectively. 3. Plasma urea specific radioactivities of the mother and infused foetus at plateau were used to determine the urea flux-rates within and between mother and foetus. The mean rate of foetal urea production (Ffo) was 1.45 and 1.63 mg/min per kg foetus in well-nourished and undernourished ewes respectively. The corresponding rates of maternal urea production (Fmo) were 0.49 and 0.37 mg/min per kg live weight respectively and there was a close correlation between the rate of maternal urea disposal (Fom) and the dietary nitrogen intake. 4. The values of Ffo were used to calculate the maximum potential for foetal gluconeogenesis from deaminated amino acids. These calculations were compared with published information on the over-all rates of foetal gluconeogenesis in well-nourished ewes. 5. The foetal entry rate of urea expressed on a body-weight basis was high, approximately 8.5 times that of the mother, but it was a threefold overestimate of Ffo. The maternal entry rate was 1.3 times Fmo and the significance of this in relation to assessing differences in urea entry rates in pregnant and non-pregnant sheep is discussed.

Animals↗
PubMed1981

Foetal and maternal rates of glucose production and utilization in chronically catheterized ditocous ewes.

1. Five well-nourished Scottish Blackface ewes carrying twin lambs were used. An umbilical artery and vein of each foetus in two sheep and one foetus in three sheep were catheterized at 109-112 days of gestation and both maternal jugular veins were catheterized 2 days before experiment. Two-day experiments were conducted between days 124 and 141 of gestation when [2-3H,U-14C]glucose was infused intravenously over 9 h into either the mother or one foetus, separate days being used for each infusion. 2. Plasma glucose specific radioactivities of the mother and infused foetus at plateau were used to determine the glucose flux rates within and between mother and foetus. The corresponding values for the uninfused foetus were calculated by using the relative weights of each twin foetus and were used to correct the maternal flux rates for the presence of the second foetus. 3. The net rate of glucose utilization by the foetus was 11.2 +/- 1.3 mg/min per kg of foetus (mean +/- S.E.M; n = 11). The corresponding rate in the mother was 1.1 +/- 0.1 mg/min per kg of live weight (n = 11). 4. The net rate of foetal uptake of glucose from the mother accounted for only 56 +/- 4% of the glucose used by the foetus. The remainder was provided by an input of 4.9 +/- 0.7 mg/min per kg of foetus to the foetal glucose pool via foetal gluconeogenesis. 5. The rate of glucose futile cycling in the foetus was high, equal to 95 +/- 19% of the net foetal glucose-utilization rate. 6. The rate of glucose utilization (mg/min per kg of foetus) decreased progressively over the observational period of 124-141 days of gestation. There was no increase in the rates of net foetal glucose uptake or of foetal gluconeogenesis to counter this decline.

Animals↗
PubMed1980

Some problems in assessing the physiological and economic significance of hypocupraemia in beef suckler herds.

Factors influencing the incidence of hypocupraemia and responses to copper therapy were investigated in three beef suckler herds calving in spring and early summer. On farm A hypocupraemia was most severe (plasma copper less than 0.4 mg per litre) in March for the cows and in October/November for their calves. On farm B plasma copper levels were 30 per cent lower in five to eight-year-old cows than in two-year-old cows in late November. Administration of copper (100 mg) in late pregnancy significantly increased plasma copper in the suckled calves on farm A but not in their dams after parturition. Growth of the calves was not increased. The alleviation of severe hypocupraemia on a third farm (C) by injecting the calf with copper did not improve growth rate. It is concluded that in some areas a severe seasonal hypocupraemia may be tolerated without loss of productivity.

Animal Feed↗
PubMed1980

Rates of glucose production and utilization by the foetus in chronically catheterized sheep.

1. Six well-nourished Scottish Blackface ewes were each prepared at 110-112 days of gestation with indwelling catheters in an umbilical artery and vein and at 2 days before experiment with catheters in each maternal jugular vein. Two-day experiments were conducted between days 124 and 134 of gestation when [2-3H,U-14C]glucose was infused over 9 h into either the maternal or the foetal circulations, separate days being used for each infusion. 2. Plasma glucose specific radioactivities at plateau were used to determine, for a two-pool model representing the glucose system of the mother and foetus, the rates of glucose production, utilization and recycling by the mother and by the foetus and the rates of transfer of glucose between the mother and foetus. 3. The net rate of glucose utilization by the foetus, which we have called the 'foetal glucose requirement', was 7.6 +/- 0.6 mg/min per kg of foetus (n = 8). Compared with the corresponding rate in the mother of 1.1 +/- 0.1 mg/min per kg of mother (n = 8), this indicated a high rate of foetal metabolism. 4. The net rate of foetal uptake of glucose from the mother accounted for only 69 +/- 5% of the foetal glucose requirement, and it has been argued that the remainder was supplied by foetal gluconeogenesis. 5. The rate of glucose recycling within the foetus was high, equal to 108 +/- 16% of the net foetal glucose-utilization rate. The significance of this in terms of either Cori or futile cycling is discussed.

Animals↗
PubMed1977

Deaths from copper toxicity of sheep at pasture and the use of fresh seaweed.

A number of sheep of the Orkney breed died of suspected copper poisoning while at pasture under circumstances which left sheep of other breeds apparently unaffected. Fresh seaweed offered to sheep with symptoms of copper toxicity appeared to be therapeutic and to lead to a reduction in plasma Cu level.

Animal Feed↗