190 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



animal is born Avithin the intact membranes and sho\ild be liber- 

 ated in order to avoid asphyxiation, but more usually a few 

 minutes or more elapse before the placenta is detached and got 

 rid of. Occasionally the membranes are retained in the uterus 

 where they are liable to become infected with bacteria and set 

 up inflanunation ; if they are not discharged steps should be taken 

 to remove them. 



The duration of parturition varies in the different species. In 

 the mare it takes from 5 to 15 minutes, in the cow about two 

 hours, in the sheep 15 minutes for each lamb born, in the sow, 

 bitch and cat from 10 to 30 minutes with sometimes an interval 

 of one hour between each birth. In the Carnivora, the mother 

 usually gnaws through the umbilical cord, but in the other 



^:.?^.M^^::- 



Fig. 100. Cow in act of calving (after Fleming, Messrs Bailliere, Tindall and Cox) . 



animals it is torn. The afterbirth may not be got rid of until 

 several hours after the 3^oung is born (as in the mare). 



The normal process of parturition depends upon the integrity 

 of the spinal cord which coordinates the various muscular move- 

 ments, but as already mentioned the uterus undergoes rhythmical 

 contractions independently of its nerve connections a;nd will do so 

 after separation from the body if maintained at the normal 

 temperature and suspended m a suitable salme fluid. Goltz has 

 shown that the bitch will give birth to pups after the complete 

 exsection of the sjDinal cord in the lumbo-sacral region, and 

 Simpson in an experiment on the sow m A^hich the posterior spinal 

 cord was destroyed showed that a litter of yomig pigs could be 

 expelled by uterine action alone, excepting for the last pigling 

 which remamed m the vagina owing to the abdommal muscles 



