title: The integration of the transfer of frozen embryos with artificial insemination in a commercial beef herd.
abstract: This trial was designed to examine the integration of the transfer of frozen embryos and artificial insemination (A.I.) in a commercial herd of beef cows. Embryos were collected nonsurgically from 15 superovulated cows and all embryos judged viable (n = 69) were frozen in 0.25 ml plastic A.I. straws. Glycerol was used as a cryoprotectant and the embryos were frozen with omission of the traditional "seeding" step. On three consecutive days immediately preceding the onset of a 60-day breeding season, 54 embryos were transferred to multiparous cows with calves at foot. The remaining 82 cows in the same herd were used as controls. Cows receiving embryos were maintained under observation, but not inseminated for 21 days, after which cows exhibiting signs of estrus were inseminated up to Day 60. Cows in the control group were inseminated at observed estrus throughout the 60-day period. The overall pregnancy rate for the experimental and control groups did not differ (77.8 % and 73.2 % respectively). Of the experimental cows, 24.1 % conceived to the embryo transfer, and 53.7 % to A.I. The mean calving to conception interval for the experimental cows was 96.3 days (median 101 days) and for the control cows it was 92.3 days (median 88 days). The calving pattern in the experimental cows was biphasic, calvings resulting from embryo transfer of A.I. accounting for the two peaks. Reconception rates in the following breeding season were not different between the embryo transfer or A.I. groups or between experimental and control herds. Weaning masses of calves born of embryo transfer were significantly higher than the other groups, but calves resulting from A.I. in the experimental herd were not different from calves in the control herd. It was concluded that the transfer of frozen embryos could be successfully integrated into an A.I. program with a limited breeding season without detrimentally affecting the overall reproductive performance of the recipient herd.
authors.affiliation: Department of Theriogenology, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa.
authors.forename: R O
authors.initials: RO
authors.lastname: Gilbert
authors.forename: R I
authors.initials: RI
authors.lastname: Coubrough
authors.forename: W J
authors.initials: WJ
authors.lastname: Ehret