Endocrinology of sex-linked-recessive dwarf White Leghorn chickens, Gallus Domesticus, with special reference to the thyroid Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9880vt56t

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  • White Leghorn chickens
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  • A comparison of the various endocrine glands, in addition to other anatomical measurements, was made on 19 normal and 21 dwarf 2-3-month-old females and 20 normal and 20 dwarf 7-13-month-old females of the White Leghorn breed. At both ages, dwarfs weighed significantly less and had significantly shorter shanks than normals. Comb weight and comb area (L X H) were significantly larger in normals than in dwarfs 7-13 months of age, but no significant difference was found in the 2-3 month age group. Ovaries in the 2-3 month age group were heavier in normals than in dwarfs, due to greater gonadotropin secretion in relation to body size. The divergent results in weight of the hypophyses on an absolute and a relative-to-body-weight basis may be attributed to the algebraic sum of synthesis storage and liberation of hormones by this gland. Also, absolute and relative weights of the adrenals did not always coincide in both age groups, which may be attributed to environmental factors influencing the release of ACTH from the hypophysis. The normals had significantly heavier thyroids than dwarfs. on an absolute and on a relative weight basis at both ages, which does not necessarily indicate a hyper- or hypothyroid condition in the latter group of birds. Normals secreted significantly more thyroxine than dwarfs at 7-13 months of age; whereas, no significant difference was found between these two types of chickens at 2-3 months of age, as determined by epithelial cell height. The significantly smaller colloid and follicle diameter found in thyroids of dwarfs than of normals may be attributed to the lower gland weights in the former group. Bioassay of the hypophyses from these chickens was conducted in immature, hypophysectomized, female rats. Dwarfs did not differ significantly from normals in STH activity, according to the tibia test, body weight gain and tail length. Greater epiphyseal plate responses were obtained from hypophyses of growing chickens. Thymus weight varied with dosage, which is attributed to several hormones acting on this gland. The normals had a significantly higher hypophyseal ACTH content than dwarfs 2-3 months of age, which is believed to be due to the hormone content of the hypophyses at the time of removal, rather than to dwarfism. Also, the younger birds were observed to have a higher ACTH content than older birds, which may be due to storage of this hormone in the hypophysis during the growing period. Dwarfs did not differ significantly from normals in gonadotropic activity at both ages, as evaluated by ovary, oviduct and uterus weight response in the assay rats. However, the older birds were observed to have higher gonadotropic activity than younger birds, as determined by ovary, oviduct and uterine weight and vaginal openings in the rats. No significant difference in FSH content of the hypophyses of dwarfs and normals of both ages was found, using ovarian follicle diameter. Observation of the interstitial cells in the rat ovaries revealed no difference between dwarfs and normals at both age classifications in ICSH content. No significant difference in TSH activity between dwarfs and normals within each age group was found, based on thyroid weight in the rats. Also, dwarfs did not appear to differ from normals of both ages in measurements on epithelial cell height and colloid and follicle diameter. Lack of appreciable differences between the treated rats and the controls in these measurements on the thyroids would indicate that rats did not respond to avian TSH.
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