326 Bulletin 162. 



AVKRAOKS OF TaHIJ-: I. 



General average including twins 182 birihs 280 days 



Average, bull calves 90 " 280 " 



cow calves 87 " 280 " 



twin calves 5 " 275 " 



By breed affinity (exclusive of twin births). 



Holstein and Holstein grades 97 births 280 days 



bull calves 51 " 280 " 



cow calves 46 " <28o " 



Jersey and Jersey grades 56 " 279 



bull calves 28 " 279 " 



cow calves 28 " 279 " 



Mixed and cross bred 24 " 283 " 



bull calves 11 " 284 " 



cow calves 13 " 282 " 



According to the age of dam (exclusive of twin births). 



From 2-year-old cows 26 births 278 days 



bull calves 14 " 277 " 



cow calves 12 " 278 " 



From 3-year-old cows 31 " 280 " 



bull calves 19 " 280 " 



cow calves 12 " 280 " 



From 4-year-old cows 29 " 281 " 



bull calves 16 " 281 " 



cow calves 13 " 282 " 



From cows 5-year-old and over 90 " 280 ". 



bull calves 40 " 281 " 



cow calves 50 " 280 " 

 In this summar}- fractions of days have been omitted which will account 

 for some apparent divScrepances, 



The statements in text books as to the period of gestation in 



the cow are commonly drawn from Earl Spencer's tables* which 



are based on the period of gestation of 764 cows of the ' ' Durham 



or improved short-horned breed" observed for several years 



previous to 1839. The averages are as follows : 



General average, 764 births 283 days. 



bull calves, 401 births 284 " 



cow calves, 340 births 283 " 



twin calves, 23 births 277 " 



In commenting on the table Earl Spencer says : "It will be 

 seen that the shortest period of gestation, when a live calf was 



*On the Gestation of Cows, by the Right Hon. Earl Spencer, Jour. Royal, 

 Agr. Society, I, 1840, p. 165. 



