Biomedical subjects
D C Davies
Publications and source records attributed to D C Davies.
Field trial to determine the efficacy of two doses of 1 alpha-hydroxycholecalciferol in the prevention of milk fever.
The efficacy of 1 alpha-hydroxycholecalciferol (1 alpha-HCC) for the prevention of milk fever has been tested in a controlled field trial using a total of 601 cows on 18 farms with a history of a high incidence of milk fever. The trial protocol proposed two doses of 1 alpha-HCC with the first injection seven days before the predicted calving date and a second injection five to seven days later if the cow had not calved. Of 301 cows receiving either one or two injections of 1 alpha-HCC, 70 had milk fever, and of 300 cows that received a placebo, 102 had milk fever. The difference in incidence between the two groups was statistically significant (P = 0.005) and indicated an overall efficacy of 32 per cent for treatment with 1 alpha-HCC. An improved efficacy was demonstrated in 67 cows that received two injections of 1 alpha-HCC with the second injection administered either on the day of calving or one day previously (60 per cent efficacy). For 42 cows that received a single injection of 1 alpha-HCC between two and five days before calving an efficacy of 79 per cent was achieved.
Differentiation of alpha-adrenergic responsiveness in the neonatal rat iris after decentralization or extirpation of the superior cervical ganglion.
The effects of stimulating alpha-adrenergic receptors in the iris of neonatal rats (up to 30 days of age) whose superior cervical ganglion (SCG) has been decentralized or extirpated 3 days after birth were investigated by measuring changes in pupil diameter. The responses of these experimental animals were compared with those of normal animals of similar age. Alpha-adrenergic stimulation was effected by topical application of noradrenaline (NA) after blockade of beta-adrenoceptors with dichlorisoproterenol and cholinoceptors with atropine. The results reveal that although decentralization of the SCG depletes the NA content of the ipsilateral iris as demonstrated by radio-chemical assay and formaldehyde-induced fluorescence, it does not affect the development of alpha-adrenoceptor responsiveness. Even the more severe disruption of the innervation caused by extirpation of the SCG did not affect the responsiveness of the ipsilateral iris.
Development of adrenoceptive and cholinoceptive responsiveness in the neonatal rat iris.
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A field trial of 1alpha-hydroxycholecalciferol (1alpha-OH D3) in the prevention of milk fever.
The efficacy of 1alpha-OH cholecalciferol for the prevention of milk fever has been tested in a controlled field trial using 597 cows on 19 farms all of which had previously had a high incidence of milk fever. Of 293 cows receiving 1alpha-OH cholecalciferol 34 had milk fever and of 304 control cows 51 had milk fever. Although there was an apparent efficacy of 31 per cent the difference in incidence was not statistically significant. There was no effect if 1alpha-OH cholecalciferol was administered less than 24 hours before the cows succumbed to milk fever. However, if 1alpha-OH cholecalciferol was administered more than 24 hours and less than one week before the occurrence of milk fever the efficacy increased to 61 per cent and the effect was highly significant.
Neuronal numbers in the superior cervical ganglion of the neonatal rat.
Neuronal numbers in the neonatal rat superior cervical ganglion were estimated from counts made on paraffin wax sections stained with cresyl violet. The raw data were separately processed in accordance with the correction procedures of Abercrombie (1946) and of Hendry (1976). The results do not support the view that there is histogenic neuronal loss during the first 30 days post-partum. Figures corrected by the Abercrombie method indicated that the neuronal population is held stable throughout the first month of neonatal life at a level of about 35000 neurons. On the other hand, when the data was corrected by Hendry's method, the population appears to increase from less than 20000 to about 45000 neurons in the first week, and is then held at that level until the end of the study period. Moreover, histochemical studies using the acid-phosphatase reaction have previously indicated that there is little or no cell degeneration during this period.
Experimental production of scrapie-resistant Swaledale sheep.
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The effects of 1alpha-OH cholecalciferol on calcium, magnesium and phosphorus metabolism in dairy heifers, and its potential value for the prevention of milk fever.
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Use of 1alpha-OH cholecalciferol in preventing post parturient hypocalcaemia and its potential value for the prevention of milk fever in dairy cows.
Cows which received 250 mug 1alpha-hydroxy cholecalciferol (1alpha-OH D3) intramuscularly within two hours after calving suffered significantly less post-parturinet hypocalcaemia and hypophosphataemia than control cows. There was a small depression in plasma magnesium concentrations in the treated cows. 1alpha-OH D3 shows potential for the prevention or treatment of milk fever.
The removal of the seminal vesicles from the boar and the effects on the semen characteristics.
A technique is described for the removal of the seminal vesicles from the boar. The operation was carried out on twelve animals and six of the animals were subsequently trained for semen collection. The seminal plasma from the boars after surgery compared with normal litter mates had a more watery consistency and did not form the characteristic gelduring ejaculation. The sperm concentration was 49% lower while the total reduction of sperm number ejaculate was 78% in the experimental animals, but the ratio of living to dead spermatozoa remained unchanged. The concentrations of citrate and protein were significantly depressed in the seminal plasma of the animals after surgery and the pH increased; the osmolarity remained unchanged. In semination of gilts with the semen from experimental boars revealed no significant loss of fertility compared with the normal controls. Animals slaughtered up to 17 months after surgery showed no regeneration of the seminal vesicles.
The establishment of sheep flocks of predictable susceptibility to expirimental scrapie.
A selection experiment, based on a foundation stock of over 700 Herdwick sheep and aimed at producing divergent populations of predictable high susceptibility or resistance to experimental scrapie was begun at this Institute in 1961. Twelve years later, flocks of presumed 100 per cent susceptibility to the Cheviot-dervied scrapie agent SSBP-1 used throughout the experiment, and also manifesting a high incidence of the disease when challenged with other scrapie strains, are used in the Compton scrapie research programme. The highly resistant flocks appear to have a small residual incidence of scrapie cases, often with very long incubation periods. The type of scrapie caused by the SSBP-1 agent is largely under the genetic control of a single pair of autosomal alleles, the dominant allele conferring susceptibility.
The surgical transfer of immature and mature Fasciola hepatica into the biliary system of the goat.
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Endotracheal intubation in the pig.
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The use of a delayed hypersensitivity test and long-acting oxytetracycline in a flock affected with ovine enzootic abortion.
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Axonal loss from the olfactory tracts in Alzheimer's disease.
Senile dementia of the Alzheimer type has been shown to be associated with impaired olfactory function early in the course of the disease. Neuropathology in the olfactory system is also a feature of Alzheimer's disease (AD) and it has been suggested that the disease may be caused by a pathogen entering the brain via olfactory pathways. To investigate this hypothesis, the effect of AD on the olfactory tract was investigated. There was a 40% decrease in the cross-sectional area of the olfactory tract and a 52% loss of myelinated axons from the tract in AD. These results, together with those of previous studies suggest that peripheral regions of the olfactory system, i.e., the olfactory bulb and primary sensory olfactory neurons are less affected by the pathology of AD than more central parts, i.e., cortical regions, the anterior olfactory nuclei, and olfactory tract. This less severe pathology at the periphery argues against a pathogen entering the brain via the peripheral olfactory apparatus and suggests a central pathogenesis which spreads centrifugally along olfactory pathways.
Milk fever, hypomagnesaemia and the 'downer cow' syndrome.
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