132 ILLUSTRATED STOCK DOCTOR. 
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Gestation of Cows. 
There has been much Surmised first and last upon the subject of the 
length of tima-xiL gestation,, .and its effect upon the sex of animals 
produced. It is, prevalent idea that if an animal goes over her time a 
male will be the result. Let us see how careful roeords kept by scientific 
men will tally with this.- 
Mr. Tessier,. a most accurate and acute observer for over forty- years, 
embracing various animals, gives results of over 575 cows and these 
subsequently having been extended to 1,131 cows the extremes were not 
changed but results as to averages are as stated below. 
Upon the 575 coWs the results were as follows : Twenty-one calved 
between the 240th and 270th days, the mean time being 259 "days! 
Five hundred and forty-four calved between the 270th and 299th days, 
the mean time being 282 days. 
Ten calved between the 299th and 321st days, the mean time bein« 
303 days. 
Earl Spencer has also carefully tabulated the period of gestation of 
cows as we find in the table on the following page. 
In these 706 cows the least period was 220 days ; the mean 285 days ; 
the longest period 313 days. He states that he was able to rear no calf 
produced at an earlier period than 240 days. Thus it may be accepted 
that, according to Tessier, a cow may carry a calf 321 days and produce 
it sound ; and from the fact .that Tessier and Earl Spencer agree almost 
■exactly as to the meantime of gestation, (1,895 cows being observed), 
285 days or nine and a half months may be taken as the average time of 
gestation of cows, slight variations being allowed from this for differ- 
ent breeds. 
Earl Spencer was inclined to the belief that a cow would carry a bull 
calf longer than a cow-calf. In stating the case, he says : 
“ In order to try this, the cows who calved before the 260th day, and 
those who calved after the 300th, ought to be omitted as being anomalous 
cases, as well as in cases in which twins were produced ; and it will then 
appear that, from the cows whoso period of gestation did not exceed 286 
days, the number of cow-calves produced was 283, and the number of 
bull-calves 234 ; while, from those whose period exceeded 286 days, the 
number of cow-calves was only 90, while the number of bull-calvea 
was 152.” 
The author, however, omitted to notice that all the calves bom after 
the 299th day were females, and of those born before the 260th day, 10 
were females and 15 males. And again, omitting the twin-calves, 340 
wero females and 401 males — a large excess of bull over cow-calves. It 
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