No abstract

We used 76 cows to determine the effect of inseminating at different times after detecting estrus and to evaluate Synchronization B as an estrus synchronizing agent. Cows were divided into five groups: (1) nonsynchronized bred naturally; (2) nonsynchronized bred once a day approximately 12 to 24 hours after detecting estrus; (3) nonsynchronized bred twice a day approximately 12 hours after estrus; (4) synchronized bred once a day, and (5) synchronized bred twice a day. Synchronizing did not affect conception rate with twice-a-day breeding, but did with once-a-day breeding. Conception rates during the first 25 days of the breeding season were 63.6, 70.0, 69.2, 40.0, 80.0 for groups 1 through 5, respectively.

One hundred seven of 112 heifers were in estrus 1 to 5 days after an injection of prostaglandin F2αgiven when a 7-day synchronization implant was removed. Checks for estrus were made every four hours and heifers were bred 6, 10, 14, 18, 22, or 26 hours after being detected in estrus. Eight heifers were not bred on schedule. Sixty-seven of 99 (67.7%) bred on schedule conceived to first artificial insemination. Conception rates were similar in heifers bred 6 to 26 hours after being detected in estrus, no differences were noted in conception rates between A.M. and P.M. breedings.

Seventy-five cows were used to compare the fertilizing abilities of sperm packaged in 0.5-ml straws and thawed in warm water to similarly packaged sperm thawed in the inseminating gun. A system of competitive mating provided for inseminating each cow twice. After cows had estrus synchronized, each was artificially inseminated with one straw of Angus semen plus one straw of Simmental semen; semen in one straw was thawed in warm water, the other in the inseminating gun. Calves produced indicated the fertilizing sperm. Of the 20 cows that conceived at the synchronized estrus, 16 conceived to warm waterthawed semen and 4 to semen thawed in the gun. These data indicate that sperm thawed in warm water before breeding were more capable of fertilization when tested in the same cow against sperm thawed in the inseminating gun.