Period of Gestation in Cows. 327 



produced, was 220 days, and the longest 313 days; but I have 

 not been able to rear an}- calf produced at au}^ earlier period than 

 242 days. An}^ calf produced at an earlier period than 260 days 

 must be considered decidedly premature : and any period of 

 gestation exceeding ;^oo days must also be considered irregular ; 

 but in this latter case the health of the produce is not affected." 



While the number of observations which we have been able to 

 make is not enough to allow of extensive generalizations, still it 

 may be permissible to generalize somewhat till more extensive 

 observations shall make possible more definite conclusions. 



The average period of gestation with us has been almost 

 exactly 280 days and is the same regardless of the sex of the 

 offspring, which is contrary to the general belief, perhaps based 

 on Earl Spencer's tables, that the male calf is carried from one 

 to three days longer than the female. The shortest period we 

 have observed is 264 days and the longest 296. This as would 

 be expected from the much smaller number of observations is a 

 much narrower range than was observed by Earl Spencer. 



While as has been said the average period of gestation is 

 almost exactly two hundred and eighty days, a close study of 

 Table I will show that the great majority of births occur from 

 the 274th to the 287th day inclusive and that within this period 

 the births are fairly equalh' distributed. It would thus appear 

 that there is a period of about two weeks on any day of which 

 the chances are approximately equal that the gestation will end. 

 The great practical importance of a knowledge of the period of 

 gestation is of course in knowing when the gestation is likely to 

 terminate so that the animal may receive the care and attention 

 that is necessary. In studying the records of individual animals 

 in this respect we have noticed that in very many cases there 

 seems to be a characteristic peculiarity of the animal as to the 

 period of gestation. We have noticed in some animals that the 

 period of gestation is uniformly either considerably longer or 

 considerably shorter than the average. In others that the same 

 rule holds true except as to a single birth which ma}' depart 

 widely from all the other births of the same animal. Wliile with 

 still other animals the period of gestation varies very widely with 

 the different births. This has seemed of so much interest that 



