Duration of Pregnancy ' 397 



uterine development. It is reasonable also to conclude that the 

 rate of development of the young will vary according to the in- 

 dividual character of the mother and may be dependent, in a 

 degree, upon her state of nutrition. 



Duration of Pregnancy in the Mare. As a general rule, 

 the duration of pregnancy in the mare is about 1 2 lunar, or a 

 trifle over 1 1 calendar months, or about 330 to 340 days. Bon- 

 net gives 11^2 to 12 lunar months (322-336 days) as the 

 normal. Dietrichs, among 500 observations, found that 80% of 

 mares foaled between 331 and 350 days. Count L,ehndorff, 

 in his text-book on horse breeding, gives a table of more than 

 8,300 records, in which the average duration of pregnancy was 

 1 1 months and 3 days. Statistics show that, in various studs, 

 the male foals were carried from J^ to 6 or 8 days longer than 

 the female. There are great variations of opinion by different 

 writers in reference to the normal duration of pregnancy. Some 

 consider normal a birth which occurs anywhere from 300 days, 

 or 10 calendar months, to 365 or more days and some even ex- 

 tend the limit to 394 or even to 420 days, as in a case given by 

 Baumeister and Rueff . 



Saint-Cyr concludes that the normal duration of gestation in 

 the mare is 340 to 350 days, between which time most foals are 

 born. Some may be born alive and continue to live, from the 

 300th day onward, while it is not rare for foals to be born up to 

 nearly 365 days. Rarely normal gestation may be prolonged to 

 400 days or over 13 months. It would seem, therefore, that 

 there may be a variation, in the period of gestation in the mare, 

 of about 100 days, or more than three months, and that we ap- 

 parently have no means for determining in advance at what time 

 a mare will foal, except that, in a general way, we may expect 

 the vast majority of births to take place between 11 and 11^ 

 calendar months. It has been alleged that breed has a certain 

 degree of influence upon the span of pregnancy and statistics of 

 Count I,ehndorff seem to indicate that, in different studs, there 

 are more or less marked differences in the duration. 



A former client, engaged in breeding pedigreed French draft 

 horses, found that, in 55 mares, the average duration of preg- 

 nancy was 336 days. Among the 13. pregnancies in one year, 

 the average was 333 days, the longest being 364 days, a 



