The Time of Ovulation in Cattle

The increased use of artificial insemination in cattle breeding has put added importance on the optimum time for mating to obtain the highest possible breeding efficiency.It is known that the life of the spermatozoa is relatively short in the female reproductive tract; consequently, the time of ovulation is of considerable importance if maximum breeding efficiency is to be obtained.The work reported here was conducted with the purpose of determining as nearly as possible at what stage of the estrual cycle ovulation occurs.Information was sought concerning the difference in time of ovulation between the types and breeds of cattle, the influence of age upon the time of ovulation, which ovary functioned more often, and the time of day ovulation was most likely to occur.No attempt was made to determine the length of estrus.The results reported in the literature on the time of ovulation in cattle have been variable and the number of animals used has been small.Hammond (6), reporting his own work and that of others, concludes that ovulation occurs spontaneously in the cow from 24 to 48 hours after the onset of estrus.In a later publication, Hammond (7) states that ovulation occurs 27 hours after the onset or just after the end of estrus.Beschlebnov (3) examined 5 cows 22 to 30 hours after mating and ovulation had occurred in all of them.In 4 others, ripe follicles were found 21 to 26 hours after mating.Nine cows examined 34 to 49 hours after breeding had all ovulated a considerable time before examination.Andreev (2) states ovulation occurs 30 to 40 hours after the onset of estrus.Kirillov (8) divided his herd into two parts.One part he mated at the beginning of estrus, the other, after 18 to 24 hours.The majority of cases indicated that ovulation occurred after 18 to 24 hours because only 26 per cent of these cows had to be rebred while 60 per cent of those bred at the beginning of estrus returned.Cole (5) states that ovulation occurs one day postestrum.Miller, Swett, Hartman, and Lewis (9) recovered a fertilized egg from the uterus of a cow 48 hours after the appearance of estrus in the cow.The second cow that they slaughtered had not ovulated.An ovum was recovered from a third cow, but it was not fertilized although she had been bred.Murphy, McNutt, Zupp, and Aitken (10) report examining a cow per rectum that ovulated between 40 and 64 hours after the beginning of estrus.