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Title: Vitamin E and egg production in heat stressed laying hens
Author: Bollengier-Lee, Sandy
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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The objective of the work described in this thesis was, firstly, to confirm that vitamin E has a beneficial effect on egg production in heat stressed laying hens and, secondly, to investigate the molecular basis of its effect. During exposure to a chronic period of heat (4 weeks at 32°C), egg production was improved in birds fed vitamin E-enriched diets. Distribution of a diet containing 250 mg vitamin E/kg diet before (4 weeks), during and after (8 weeks) the period of stress increased egg production by 12% (P<0.02) during and by 13% (P<0.02) in the four weeks following the stress control birds (fed 10 mg vitamin E/kg diet). Egg formation involves the mutually dependent activities of the ovary (uptake of yolk precursors and synthesis of oestrogens) and of the liver (oestrogen induced-synthesis of yolk precursors). Neither heat stress nor vitamin E were found to have direct effects on the in vivo uptake of the main yolk precursor protein, vitellogenin, by oocytes or on the circulating concentration of 17β-oestradiol. Although the amount of vitellogenin messenger RNA in hepatocytes and vitellogenin protein in the circulation were significantly depressed during heat stress in non-supplemented birds, the concentration of vitellogenin protein in hepatocytes was dramatically increased in these birds (+63%, P<0.01) compared to pre-stress values. In vitamin E-supplemented birds, this accumulation of vitellogenin protein in hepatocytes did not occur and the circulating vitellogenin concentration was higher than in non-supplemented birds. It is therefore proposed that, during heat stress, vitamin E improved the export of vitellogenin from the liver into the circulation. This effect is probably related to the known antioxidant properties of vitamin E and to its consequent protective effect on the integrity of organelle and plasma membranes which is required for proper export of proteins through the secretory pathway.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available