Essentials of Animal Breeding. 



9 



Gestation period of various animals. 



Mare 11 months (340 days). 



Jennet 12 months (365 days). 



Cow 9i months (280 days). 



Ewe 5 months (150 days). 



Goat 5 months (150 days). 



Sow 4 months (114 days). 



Probable date of birth of young, female bred on first day of the month (Sewall 



Wright). 



Variations in the period of gestation for animals of the same kind 

 are not readily explained. Some animals, such as sows, are quite 

 uniform in the length of the gestation period. In mares there is a 

 considerable variation. It has been suggested that in mares some 

 time may elapse between the moment of service and the actual fer- 

 tilization of the egg by the sperm cell. In guinea pigs the size of 

 the litter affects the period of gestation, the period being shorter for 

 a large litter than for a small one. The health of the mother during 

 pregnancy also has an effect. 



During the gestation period the young animal is carried in the 

 mother's womb and is not connected directly with her body. The 

 blood vessels and nerves of the mother do not connect with those of 

 the growing embryo, but from the start the little one has its own 

 little system of circulation and its own nervous system. It is carried 

 in an enveloping sac which is attached to the wall of the mother's 

 womb by buttons (cotyledons) which become detached when the time 

 comes. The, young are nourished by blood passing from the mother's 

 body through the walls of the uterus into the sac in which the fetus 

 is carried, and thence into the body of the young animal by trans- 

 fusion, much as water would pass into a paper sack if you should 

 lower it into a bucket of water. 

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