150 OBSTETRICAL FHYsRiLOGV. 



3. Births are frequent between 325 and 340 days, 



4. They are not rare from 350 to 365 days, but they are indeed so 

 after the latter period. 



5. We may consider 300 to 400 days as the extreme limits within 

 which normal gestation occurs in the Mare ; below or beyond these it 

 ceases to be natural and really physiological. 



6. According to the researches of M. Gayot, pregnancy is often a little 

 longer for a Colt than a Filly ; and though this conclusion is certainly 

 not founded on a sufficiently large number of observations, it neverthe- 

 less acquires a certain degree of probability from being in conformity 

 with what is observed in the Bovine species. 



The average duration of pregnancy with thirty-three thoroughbred 

 Mares which foaled at the celebrated Middle Park Stud, Eltham, in 

 1876, T find on examination to be 335i days — the shortest periods being 

 316 days (one instance), and 318 days' (one instance) ; and the longest 

 354 days (one instance), and 348 days (one instance). Between the 

 320th and 330th days, there were only 5 instances ; between the 330th 

 and 340th days, there were 11 instances ; and between the 340th and 

 348th days there were 15 instances. Owing to some of the Mares 

 having been put to the Horse more than once, and in some cases at 

 intervals of several days, the averages may not be absolutely correct, as 

 the last coitus has been the one which is reckoned from!^ But with 

 one Mare (Entremet) put only once to the Stallion (Rosicrucian), the 

 period was 324 days ; with another (Hilda) put to the same Stallion, the 

 period was 332 days ; and with another (Imogene) and this StalHon, it 

 was 342 days. 



With regard to sex, there were sixteen Colts and seventeen Fillies: the 

 average gestation period of the former was 336^ days, and the latter 

 334 days. The shortest periods (316 and 318 days") were with Fillies, and 

 the longest periods were also with Fillies (354 and 348 days). The ages of 

 the Mares ranged from five to nineteen years ; there being three at five, 

 two at six, three at seven, two at nine, two at ten, six at twelve, four at 

 fourteen, four at fifteen, two at sixteen, one at seventeen, one at 

 eighteen, and three at nineteen. In the first group, pregnancy averaged 

 340 days ; in the second 3501 days ; in the third 3281^' days ; in the 

 fourth 340i days ; in the fifth 336 days ; in the sixth 337V.r davs ; in the 

 seventh 336.i days ; in the eighth 333 days ; in the ninth 3401 days ; in 

 the tenth 324 days ; in the eleventh 330 ; in the twelfth 325. These 

 figures would go to prove that the period of gestation decreases with age ; 

 and indeed we find that the shortest pregnancies occurred in Mares 

 nineteen years old (316 and 318 days), and the longest in six and nine 

 years old Mares (354 and 348 days). 



The animals were of course kept in the most favourable conditions 

 for breeding; and this, with their splendid qualities and precocity, 

 doubtless shortened the period of gestation, which is below the ordinary 

 average. 1 



An extensive horse-breeder in Oregon, U.S.A., has been making some interesting 

 observations on the duration of pregnancy in jMares, as influenced by the season. He 

 writes : " On the 20th of .Tuly, 1879, I bred a Mare, and bhe foaled on the 30th of the 

 following May. The next spring I bred my Mares early, and they carried their Foals 

 about eleven and a half months. "The thought occurred to me then that Mares bred early 

 in spring carried their Foals longer than those bred later. For the next two seasons I 

 took charge of a band of Mares, and found that those bred in April carried their Foals 

 longer than those bred in Maj-, and that those bred in May went longer than those bred 

 in June and .Tuly. Since then I have had considerable bad luck with ujy Mares getting 



