REPRODUCTIVE CYCLE IN FEMALE VERTEBRATES 



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cycle of the mammal relative to fertilization or the bringing together of the 

 male and female reproductive cell. One aspect is the sexual receptivity of 

 the female; the other is the time of ovulation of the egg. In most female mam- 

 mals sexual receptivity and ovulation are intimately associated and occur 

 spontaneously in the cycle; in others the two events may be separated. In 

 the former group, the development of "heat" and the maturing of the egg 

 follicle are closely associated, while in the latter the conditions favoring sexual 

 receptivity or heat are developed considerably in advance of the maturation 

 of the follicle, as noted in the table below. 



b. Relation of Estrus and Ovulation in Some Common Mammals 



1) Spontaneously Ovulating Forms (Sexual Receptivity of Male Occurs at 

 or near Time of Ovulation): 



Length of Estrus or Period 

 of Heat 



Time of Ovulation 



Dog 



Guinea pig 

 Man 



True period of heat about 

 5-10 days in the middle of 

 a 21 -day estrous period 



6-11 hrs. 



Receptivity not always related 

 to cyclic events 



Variable: 1st day; 2nd day; 5th day; 

 etc., of true period of heat 



Views vary: 1-2 hrs. after heat or 

 estrus begins; 10 hrs. after; at end 

 of estrus 



12-17 days after onset of preced- 

 ing menstruation; average around 

 14th day 



About 1-2 days before end of es- 

 trus; best breeding about 3 days 

 after heat begins 



Late in estrus or just after estrus 

 ends; presumably about 20-36 

 hrs. after estrus begins 



About 1-3 days after onset of estrus 



1st or 2nd day of estrus 



8-11 hrs. after beginning of heat 



2) Dependent Ovulatory Forms (Sexual Receptivity [Heat] Occurs Pre- 

 vious to Time of Ovulation): 



Length of Estrus or Period 

 of Heat 



Time of Ovulation 



Cat 



2-3 days 



Time of ovulation uncertain but is 

 dependent upon copulation 



