THYROID FEEDING AND SECONDARY SEX CHARAC- 

 TERS IN RHODE ISLAND RED CHICKS. 



HARRY BEAL TORRE Y AND BENJAMIN HORNING. 



In an earlier paper 1 we called attention to the precocious ap- 

 pearance of the second set of rectrices in Brown Leghorn chicks 

 whose daily ration from the fourth week after hatching had 

 included dessicated thyroid. Reference was made also to another 

 case of precocious development of rectrices, namely in Rhode 

 Island Red male chicks, 2 as a result of thyroid feeding. And, 

 correlated with the early appearance of the rectrices in the latter 

 was a failure of the feathers on the neck to differentiate into the 

 hackles characteristic of the control males. The acceleration of 

 rectrices and absence of hackles of the male type combined to give 

 to the plumage of the thyroid-fed males an aspect so strikingly 

 female as to deceive even experienced poultry fanciers. Comb, 

 wattles, carriage of the body and behavior remained, however 

 characteristically male. The accompanying tables present 

 typical facts and the figures typical birds. 



Table I. shows the effect of thyroid feeding in one experiment on 

 the development of the first rectrices in Rhode Island Red chicks. 

 When the latter were four weeks old, they were divided into two 

 lots as indicated in the table. To each bird of one lot a capsule of 

 Armour's desiccated thyroid, containing .2 per cent. I, was given 

 daily. For the first two weeks the dose was 50 mgms. ; for the 

 next three weeks, 100 mgms. ; for the next three weeks, 150 mgms. 

 The other lot served as a control. All birds were twelve weeks 

 old when recorded. 



Figure I is from a photograph of the typical bird recorded as 

 No. I, Table I., at the age of twelve weeks. The rumpless con- 

 dition is characteristic of normal Rhode Island Red males at this 

 age. It is due to the fact that the first set of rectrices customarily 



1 Torrey and Horning, The Effect of Thyroid Feeding on the Moulting Process 

 and Feather Structure of the Domestic Fowl, BIOL. BULL., XLIX, 1925, 275. 



2 Torrey and Horning, Hen Feathering Induced in the Male Fowl by Feeding 

 Thyroid, Proc. Soc. Exper. Biol. and Med., XIX., 1922, 275. 



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