HORMONES AND MATING BEHAVIOR 



1211 



Henderson, 1947) should be regarded as an 

 adverse effect of the thyroid substance given 

 these animals. Blaxter's (1952) comment, 

 however, on the claim that cows are more 

 difficult to get to calf following the feeding 

 of iodinated casein should be noted. 



"The interpretation of such data is ex- 

 tremely difficult and cannot warrant the con- 

 clusion they drew. In other experiments with 

 Jersey cows given iodinated casein through- 

 out the larger part of their lactation the 

 cows reproduced quite normally. Holstein 

 cows, under the same conditions, however, 

 failed or were slow to conceive. Some of these 

 cows were closely related and the small num- 

 bers (total 20) again make conclusion diffi- 

 cult. In Crichton's experiments lasting for 

 4 years, neither the interval between calvings 

 nor the number of services necessary for con- 

 ception revealed any effect of either io- 

 dinated protein or ^-thyroxine administra- 

 tion on reproductive performance. 



"There is thus no reliable evidence of any 

 gross abnormality in the reproductive per- 

 formance of the hyperthyroid dairy cow. At 

 the same time there is insufficient evidence 

 available to judge whether a small impair- 

 ment does not in fact take place." 



Numerous reports state that the strength 

 of sexual behavior was reduced if not abol- 

 ished in hypothyroid males and females 

 (Rickey, 1925, in thyroidectomized male 

 rats; Petersen, Spielman, Pomeroy and 

 Boyd, 1941, in the thyroidectomized bull; 

 Brody and Frankenbach, 1942, Spielman, 

 Petersen, Fitch and Pomeroy, 1945, in thy- 

 roidectomized cows; Blivaiss, 1947a, b, in 

 thyroidectomized brown Leghorn hens and 

 roosters; Maqsood, 1952, in thyroidecto- 

 mized and thiouracil-fed male rabbits; Pe- 

 terson, Webster, Rayner and Young, 1952, 

 in thyroidectomized, but not in propylthi- 

 ouracil-fed, female guinea pigs). A restora- 

 tion of sexual behavior followed the feeding 

 of thyroid substance to the bull and cows. 

 After a rest of 90 days the administration of 

 a single 5-gm. dose of dinitrophenol to the 

 bull restored normal activity and sexual be- 

 havior in 12 hours. The elevation in metabo- 

 lism seems to have been regarded as the 

 common denominator. 



Rickey (1925) noted that thyroidecto- 

 mized female rats mated, and Lee (1925) 



reported that thyroidectomized female rats 

 showed the same heat reactions when placed 

 with males that were displayed by normal 

 females. Folley (1938) stated that 3 weeks 

 after weaning no difficulty was encountered 

 in mating 8 of 10 rats thyroidectomized dur- 

 ing lactation. Treatment with antithyroid 

 drugs did not prevent female (Krohn and 

 White, 1950; Leathem, 1951) or male (Jones, 

 Delfs and Foote, 1946) rats from mating. 

 Chu (1945) states that 14 thyroidectomized 

 female rabbits became pregnant 17 to 108 

 days after the operation and Krohn (1951) 

 writes that, although thyroidectomized rab- 

 bits were occasionally reluctant to mate, in 

 general they did so and brought their litters 

 to term. There was said to be no evidence of 

 infertility when thyroidectomized hens and 

 roosters were mated (Greenwood and Blyth, 

 1929). As we have noted, thyroidectomy of 

 the female guinea pig was followed by a re- 

 duction in the percentage found in heat, but 

 it did not prevent all from coming into heat 

 and mating (Petersen, Webster, Rayner 

 and Young, 1952). Daily injections of thy- 

 roxine for several weeks increased general 

 excitability as reflected in heightened startle 

 reflexes, but did not raise sexual excitability 

 in the male rat (cited as unpublished, Beach, 

 1942e). 



From these results it is apparent that re- 

 productive processes, including the display 

 of mating behavior in the male and female, 

 often require a functioning thyroid gland, 

 that a level of thyroid activity exists which 

 is optimal for reproduction, and that devia- 

 tions in either direction may be followed by 

 changes in if not the elimination of mating 

 behavior. But a considerable deviation can 

 occur without preventing reproduction and 

 therefore mating. Something of the range 

 within whicli mating can occur is indicated 

 by data presented in three studies. Following 

 thyroidectomy of 32 female rabbits the 

 basal metabolic rate fell 25 to 30 per cent 

 below normal, but in tests of their reproduc- 

 tive performance the animals were mated 63 

 times (Sax and Leibson, 1937). In a later 

 experiment involving thyroidectomy and 

 treatment with a thyroid preparation the 

 range of basal metabolic rate within which 

 mating occurred was 1.56 to 3.32 cal. per kg. 

 per hour (Sachs, 1939). Not all the female 



