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T. L. AVERY and E. F. GRAHAM

Summary.

Recovery of ova was effected by slaughter of the donor and removal and flushing of the reproductive tract. A significantly greater percentage of ova were recovered from cows than from calves. Cow ova were fertilized at the rate of 61·49% while fertilization rate of calf ova was 23·6 %. A significantly greater percentage of cows, not possessing corpora lutea at breeding, produced more fertilized ova than did cows possessing a 'full-sized' corpus. The administration of stilboestrol to cows possessing 'full-sized' corpora lutea was observed to significantly increase the percentage of fertilized ova recovered from 14·29 to 66·6%. Also, the administration of stilboestrol increased the percentage of fertilized ova recovered from calves, and permitted the collection of fertilized ova from pregnant cows.

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T. L. AVERY, C. L. COLE and E. F. GRAHAM

Summary.

Synchronization of bovine oestrous cycles was studied with respect to methods of accomplishment. A total of 328 cows were recycled by: (a) daily subcutaneous injections of progesterone, (b) larger subcutaneous injections every 3rd day and (c) corpus luteum expression. Standing oestrous was exhibited by 262 cows. Twelve did not exhibit oestrus and fifty-four exhibited symptoms but refused mounting. Time between treatment and oestrus was 4·97 ±1 82, 6·52 ±1 ·25 and 2 ·84 ±0·68 days, respectively, for the three methods employed. Length of time between injection and oestrus did not differ significantly as influenced by day of initiation, the duration of injections or by superovulation. Differences between fifty-nine recycled and fifty-three control cows, with respect to rate of conception, were not significant nor were differences between the first and second services after recycling.

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T. L. AVERY, M. L. FAHNING and E. F. GRAHAM

Summary.

(1) Purified swine fsh and lh effectively induced superovulation in mature and immature as well as pregnant bovine females. Sixty-one of seventy-five treated cows and calves ovulated, producing a total of 1716 ovulation points which ranged from one to eighty-eight with a mean of 28·13. Twenty-eight of thirty-two cows and thirty-three of forty-three calves responded to treatment by ovulating. Calves produced an average of 12·46 more ovulations than did cows. (2) Neither the addition of prolactin to the ovulatory dosage of lh nor the administration of lh for 2 consecutive days proved superior to the single injection of lh as an ovulatory procedure for calves. (3) Calves produced 54·03% of their total ovulations on the right ovary compared to 51·17% for cows. (4) Nineteen cows, having undergone oestrus synchronization, produced an average of 7·89 ovulations more than were produced by nine similar individuals, superovulated without prior treatment with progesterone. (5) 60·21% of all cows superovulated demonstrated oestrus. A significantly greater number of cows receiving progesterone as well as those undergoing enucleation of corpora lutea exhibited oestrus than did cows not receiving treatment prior to superovulation. (6) Superovulated cows exhibiting oestrus produced an average of 3·82 ovulations more than were produced by superovulated cows failing to show heat.

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T. L. AVERY, M. L. FAHNING, V. G. PURSEL and E. F. GRAHAM

Summary.

Thirty inovulations of bovine ova were conducted. Superovulated ova as well as ova from single points of ovulation were transferred by both surgical and non-surgical means to synchronized and non-synchronized recipients. Two transfers entailed the use of follicular ova.

None of fourteen non-surgical transfers, made via the cervix or via the rectum, definitely resulted in pregnancy, nor did twelve transfers conducted by depositing ova within the peritoneal cavities of selected hosts.

One of four transfers, conducted by means of laparotomy, resulted in pregnancy and terminated in the full term birth of a 98-lb bull calf.