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Biomedical subjects

W A Dewar

Publications and source records attributed to W A Dewar.

At least 19 recordsLinked to original sources
PubMed1989

Regulation of net intestinal calcium uptake in hens laying obligatory soft-shelled eggs.

1. Individually caged laying hens had a loop of thread inserted into the shell gland. This resulted in the laying of soft shelled eggs. 2. A balance study was performed for a one week period before and after the operation. After the operation birds with threads consumed less calcium than before. Their requirements for calcium for eggshells decreased, resulting in increases in both calcium excreted and calcium retained. 3. Net calcium extraction in the digestive tract was measured in groups of birds with threads and intact controls, when shelling or not, by examining ratios of Ca to TiO2 in different gut segments. Observations were made during the period following premature oviposition in birds with threads, but within the normal shelling period of control birds. The period of study was at least two weeks after the operation. 4. Birds with threads absorbed less calcium than control birds up to the upper jejunum. 5. Control birds secreted calcium between the upper jejunum and colon, but birds with threads showed little change in absorption in this part of the digestive tract. 6. The increase in calcium absorption in intact birds was a response to the stimulus of shelling an egg or replacing calcium in medullary bone during a pause day, rather than of ovulation.

Animals↗
PubMed1984

The zinc requirements of broiler chicks and turkey poults fed on purified diets.

Chicks and turkey poults were fed for 3 weeks on low-zinc diets, prepared from purified ingredients, supplemented with zinc oxide at graded levels. Birds of both species given the unsupplemented basal diets grew poorly, with high mortality rates. All had severe hyperkeratosis but bone development was normal. Only when birds received diets with low concentrations of added Zn were leg abnormalities observed. Zn requirements were assessed visually from dose-response graphs. The chick required 18 mg Zn/kg diet for maximal live weight and 24 mg Zn/kg for maximal Zn concentration in blood serum. The responses of tibial Zn and net retention of Zn did not reach plateaux within the range of dietary Zn concentrations studied. The turkey poult's Zn requirement for maximal live weight was 25 and 28-29 mg/kg for net retention of Zn and for maximal concentration of Zn in blood plasma and in the tibia; 41 mg Zn/kg diet was required for maximal Zn in blood serum. Liver Zn was not correlated with dietary Zn in either species.

Animals↗
PubMed1983

Toxic effects of high concentrations of zinc oxide in the diet of the chick and laying hen.

The effects of high dietary concentrations of zinc oxide on chicks and hens were studied in four experiments. Chicks given 2000, 4000 or 6000 mg zinc/kg diet from 2 to 6 weeks of age grew poorly, many showing gizzard erosion and lesions of the exocrine pancreas. Dissecting aneurysms occurred in a few birds receiving 6000 mg zinc/kg. Pancreatic lesions were found in chicks maintained on 1000, 2000 or 4000 mg zinc/kg from 0 to 4 weeks and the two higher concentrations reduced body weight and increased the incidence of gizzard erosion. Histologically, gizzard lesions varied from excessive desquamation of epithelial cells, heterophils and erythrocytes into an abnormally spongiform koilin, to erosion of koilin, glands and pits. Pancreatic lesions could be detected only microscopically and consisted of dilation of the acinar lumina, cytoplasmic vacuolation, cytoplasmic globule formation and necrosis of the exocrine cells with interparenchymal fibrosis. Similar lesions of the gizzard and pancreas were found in hens after they had received 10000 or 20000 mg zinc/kg diet for only 4 d. Hens given 10000 mg zinc/kg for 4 d followed by a normal zinc intake for 28 d had normal gizzards and pancreata.

Aortic Dissection↗
PubMed1982

The contribution of anorexia to reduced growth in zinc-deficient chickens.

1. It was shown, using a paired-feeding technique, that the growth depression in zinc-deficient chicks was largely caused by the greatly reduced consumption of the deficient diet. 2. Chicks receiving a zinc sulphate solution directly into the crop ate an amount of zinc-deficient diet similar to that of the zinc-deficient diet eaten ty the control chicks; palatability was thus ruled out as the cause of the anorexia. 3. Only chicks receiving the zinc-deficient diet displayed signs of zinc deficiency.

Administration, Oral↗
PubMed1981

The effects of zinc deficiency on oral behaviour and taste bud morphology in chicks.

The number of beak and tongue movements was measured in chickens (Gallus domesticus) following oral stimulation with different concentrations of quinine hydrochloride (0.01 to 0.25 M), acetic acid (0.25 to 5.0 M), sodium chloride (0.5 to 5.0 M) and distilled water. The birds showed an increase in behaviour with increasing concentration up to a certain point, when the response showed no further increase. 2. Two groups of chicks, one fed on a normal diet and one fed on a diet deficient in zinc, were stimulated orally every 3 to 4 d with 0.1 ml of sodium chloride (2 M), acetic acid (2 M), quinine hydrochloride (0.1 M) and water, and the numbers of beak and tongue movements were recorded. 3. All the birds fed on the zinc-deficient diet showed significant increases in beak and tongue movements compared with the control birds. The time of onset of this increase in behaviour was variable: with quinine hydrochloride it was 3 d whereas with acetic acid, sodium chloride and water it was between 6 and 9 d. 4. The morphology of the taste buds in zinc deficiency was investigated and there was no evidence of primary or preferential involvement of the taste buds; these structures were either morphologically normal or were involved in a generalised degeneration of the epithelium. 5. The increase in oral behaviour is discussed in relation to the possible ageing of the taste cells and to the general degeneration of the oral epithelium.

Acetates↗
PubMed1981

The effects of vitamin A deficiency of oral gustatory behaviour in chicks.

1. Two groups of chicks (Gallus domesticus) were fed on a vitamin A-deficient diet for 24 d. Birds in one group, which acted as a control, were dosed orally with retinyl palmitate in corn oil, whereas the other group (experimental) was given corn oil only throughout the experiment. 2. At regular intervals birds in both groups were stimulated, orally with solutions of acetic acid, quinine hydrochloride and sodium chloride and the number of beak and tongue movements counted. 3. By the end of the experiment the vitamin A-deficient birds showed a significant decrease in their response to the oral stimulants compared with the control birds.

Acetates↗
PubMed1976

The histopathology of zinc deficiency in ducks.

Ducks maintained from hatching on zinc-deficient diets were retarded in growth and had severe lesions of the pedal epidermis, epithelia of the base of the tongue, oral surface of the larynx and nasal sinuses. Similar but milder changes affected the roof of the mouth, the crop and the oesophagus of a few cases. There was derangement of the architecture of the rete mucosum with loss of distinction between the cells of the stratum basale and stratum spinosum. Enlargement of the nuclei and nucleoli of these cells, widening of the intercellular space and dyskeratosis and degeneration, particularly of the prickle cells, were seen. Although epithelial atrophy occurred in early examples of the condition, acanthosis, hyperkeratosis and heterophil infiltration of the epithelial layers were characteristic of most cases. Erosion of the epithelium with the formation of purulent crusts ocntaining secondary bacterial foci was present and in these cases inflammatory phenomena occurred in the dermis. A small proportion of the nuclei of the pancreatic exocrine cells were enlarged and irregular in shape.

Animals↗
PubMed1976

Dietary chloride requirement of broiler chicks fed on a wheat-soya bean diet.

1. A diet based on soybean meal and wheat contained insufficient chloride to support normal growth in chicks. 2. Ammonium chloride and sodium chloride were equally good sources of supplementary chloride for the chick. 3. When seven diets providing increasing proportions of chloride from 608 to 1808 mg/kg, were fed to chicks, maximal growth at 21 d was obtained at about 1200 mg chloride/kg diet.

Ammonium Chloride↗