REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1117 



and James (1949) show that the chicken 

 ovary may weigh 2 gm. at 150 days of age 

 and 20 gm. at 180 days. A single follicle 

 may increase in weight from 1 to 16 gm. in 

 9 days. The yellow yolk deposited during 

 this phase is rich in lipids (50 per cent of the 

 dry matter) ; it contains large amounts of 

 cholesterol and is rich in vitellin. 



The mechanism of yolk deposition is 

 poorly understood, especially the apparent 

 change in the selective permeability of the 

 follicular membranes during the three 

 phases of follicular growth and yolk forma- 

 tion. Although changes in the blood chemis- 

 try under the influence of estrogen in all 

 probability play a role in mobilizing the 

 yolk precursors, these changes do not guar- 

 antee the deposition of yolk in the follicle. 

 Undoubtedly, the anterior pituitary hor- 

 mones influence the permeability of the fol- 

 licular membranes, but how they do so is 

 not known. 



Endocrine activity of the ovary and 

 THE EFFECTS OF HORMONES. Adequate evi- 

 dence exists to show that the avian ovary 

 secretes three hormones, estrogen, androgen, 

 and progesterone. Evidence for the secretion 

 of each of these hormones will be presented 

 together with the physiologic effects of the 

 hormones as they pertain to reproduction. 



1. Estrogen. Estrogen secretion by the 

 ovary was demonstrated by Mario w and 

 Riehert ( 1940) by extraction procedures 

 followed by bioassay of the extract. Sub- 

 sequent chemical analyses demonstrated 

 that the ovary of the laying hen contains 

 estradiol, estrone, and estriol (Layne, Com- 

 mon, Maw and Fraps, 1958). Estrone is 

 present in the blood in the conjugated frac- 

 tion. Kornfeld and Nalbandov (1954) had 

 previously demonstrated the presence of 

 a biologically active estrogen in the blood 

 of 16- to 20-day-old pullets. The evidence 

 strongly favors the concept that estrogen 

 is secreted by the ovary and that secretion 

 starts during embryonic development (see 

 chapter by Burns). The thecal gland cells 

 are considered to be the source of estrogen 

 (Marshall and Coombs, 1957). 



Estrogens have many effects on the physi- 

 ologic processes of birds. Extensive reviews 

 have been published on various aspects of 

 the effects of estrogens (Nall)andov, 1953; 



Lorenz, 1954; Sturkie, 1954; Stammler. 

 Katz, Pick and Rodbard, 1955; Urist, 1959) , 

 so only the most salient features will be 

 mentioned here. 



Estrogen administration causes an en- 

 largement of the oviducts and its ligaments, 

 an effect which will be discussed more ex- 

 tensively later in this chapter. In addition 

 to this effect on a secondary sex organ, 

 estrogens cause marked changes in the 

 composition of the blood which are sum- 

 marized in Table 18.5. The substantial 

 agreement with respect to their nature 

 makes it unnecessary to include all the pub- 

 lications on this subject. Extensive further 

 documentation can be found in the reviews. 



Investigations have been conducted in 

 order to determine the mechanisms involved 

 in the production of some of the changes 

 in blood composition. The lipid and phos- 

 pholipid responses can be obtained in chick- 

 ens on a fat-free diet and in hypophysecto- 

 mized chickens (Baum and Meyer, 1956). 

 The responses require the normal function- 

 ing of the liver (Ranney and Chaikoff, 

 1951 ; Vanstone, Dale, Oliver and Common, 

 1957). The increases in plasma protein and 

 phosphoprotein are also dependent on nor- 

 mal functioning of the liver (Vanstone, 

 Dale, Oliver and Common, 1957). Thyroid 

 hormone administration together with estro- 

 gen abolishes the estrogen-induced lipemia 

 (Fleischmann and Fried, 1945; Hertz, 

 Schricker and Tullner, 1951), proteinemia 

 (Sturkie, 1951), increase in serum vitellin 

 (Hosoda, Kaneko, Mogi and Abe, 1954), 

 increase in biotin (Hertz, Dhyse and Tull- 

 ner, 1949), and calcemia (Fleischmann and 

 Fried, 1945). The mechanism of this inhibi- 

 tion is not clear, but it seems to involve a 

 different mechanism of action of estrogen 

 from that which produces oviducal growth, 

 for estrogen-induced oviducal development 

 is not affected by simultaneous thyroxine 

 treatment (Fleischmann and Fried, 1945; 

 Hertz, Schricker and Tullner, 1949; Hosoda, 

 Kaneko, Mogi and Abe, 1954) . 



Intensive studies have been made of the 

 effect of estrogen on calcium metabolism; 

 Urist (1959) has given a detailed account. 

 He established that administration of 100 

 mg. estrone jier week to either roosters or 

 laying hens caused the deposition of large 



