REPRODUCTIVE ENDOCRINOLOGY IN BIRDS 



1119 



Ca is probably partly, if iiot completely, 

 the result of postoperative starvation (Po- 

 lin and Sturkie, 1957). 



0. Parathyroidectomy of estrogen- 

 treated capons or roosters reduces the 

 estrogen-induced increase of diffusible cal- 

 cium to about 58 per cent of the pre-opera- 

 tive level, whereas the nondiffusible Ca is 

 only slightly affected. The diffusible cal- 

 cium levels obtained after this treatment 

 were similar to those obtained in parathy- 

 roidectomized birds without estrogen treat- 

 ment (Polin and Sturkie, 1958). 



d. Estrogen treatment after parathy- 

 roidectomy results in an increase of the 

 nondiffusible Ca in cocks and capons, de- 

 {lending on the level of diffusible Ca pres- 

 ent. The higher the latter the greater the in- 

 crease in nondiffusible Ca after estrogen 

 administration. These data indicate that es- 

 trogen can cause an increase in blood cal- 

 cium when the parathyroids are functional 

 or when enough diffusible Ca is present in 

 the blood. Polin and Sturkie (1957) pro- 

 posed that the level of diffusible Ca in the 

 blood regulates the activity of the parathy- 

 roids. The hormone from this gland must 

 maintain a certain level of diffusible Ca in 

 order to make the estrogen-induced in- 

 crease in nondiffusible Ca possible (Polin 

 and Sturkie, 1958). Thus estrogen-induced 

 high nondiffusible Ca levels coincide with 

 deposition of the resorbed substance. The 

 discontinuation of estrogen administration 

 produces resorption of the intramedullary 

 bone (Urist, 1959). This resorbate may be 

 transported as diffusible Ca, because, after 

 estrogen treatment, the nondiffusible Ca as 

 well as the phosphoprotein levels decrease. 

 Nondiffusible Ca seems to be closely asso- 

 ciated with the phosphoprotein. According to 

 Urist, Schjeide and McLean (1958), the 

 phosphoprotein deposited in the yolk is de- 

 posited with the full complement of Ca that 

 it carried in the serum. In none of the hy- 

 potheses made has an explanation been 

 given for the increased parathyroid size 

 and activity observed after estrogen ad- 

 ministration. This may mean that the in- 

 creased parathyroid activity is coincidental 

 or that the parathyroid is involved in a 

 manner not yet accounted for. 



The mechanisms bv wliicli estrogen mobi- 



lizes the various components which are de- 

 posited in yolk are still largely unknown, 

 although the site of action seems to be the 

 liver. The importance of mobilizing the 

 yolk precursors will be discussed under the 

 endocrine regulation of ovarian activity. 



Increased appetite has been observed 

 after the administration of "artificiar' estro- 

 gens (Lorenz, 1954; Baum and Meyer, 

 1956; Hill, Carew and van Tienhoven, 

 1958). Such stimulation of appetite may be 

 an important adaptive mechanism in birds 

 to provide for the deposition of large 

 amounts of high energy materials in the 

 yolk. It has, however, not been determined 

 whether or not natural estrogens have the 

 same appetite-stimulating effect in birds as 

 the artificial estrogens. In experiments 

 which the author was able to find in the 

 literature, in which naturally occurring es- 

 trogens were used in birds, pair feeding was 

 practiced. Thus, the possible appetite stim- 

 ulating effect could not be evaluated. The 

 possibility of a difference in effect on appe- 

 tite regulation by naturally occurring and 

 artificial estrogens was revealed in experi- 

 ments with rats by Meites (1949). This 

 author found that diethylstilbestrol (DES) 

 inhibited food consumption in rats whereas 

 estrone had no effect. 



AVhether the appetite-stimulating effect 

 of artificial estrogens in chickens is the re- 

 sult of a direct stimulation of appetite cen- 

 ters in the hypothalamus or an indirect ef- 

 fect mediated by a change in the blood or in 

 fat deposition has not been established. 



The influence of estrogen on feather de- 

 velopment has been extensively reviewed by 

 Domm (1939) and by Benoit (1950a); 

 little needs to be added to their conclusions. 

 In most species in which sexual dimorphism 

 occurs and in which the male has the more 

 ornamental plumage, estrogens are responsi- 

 ble for the female type of feathering (so- 

 called hen feathering). It is apparently true 

 for the chicken, turkey, mallard, ostrich, 

 pheasant iPhasianus colchicus and Phnsia- 

 nus colchicus X gennaeus nyethemerus, Pha- 

 sianus colchicus torguatus) and bobwhite 

 quail (Colinus virginianus) that the male or 

 cock feathering is due to the absence of es- 

 trogen. In all these birds (sinistral) ovari- 

 ectomy results in male type feathering, the 



