Fixed-time insemination of porcine luteinizing hormone-treated superovulated beef cows and the resynchronization of beef cows for fixed-time embryo transfer

摘要

Two trials were conducted to compare the effectiveness of fixed-time artificialinsemination (AI) to AI based upon visual detection of estrus following superstimulationof donor beef cows. In Trial 1, multiparous beef cows (n = 31) were randomly allotted toone of three treatments following superstimulation and removal of an intravaginalprogesterone insert (CIDR). Cows in the Control group were inseminated at 12 and 24 hafter onset of estrus. Cows in the Estradiol group were injected with estradiol-17? (1 mg,im) at 12 h and inseminated at 24 and 36 h after CIDR removal. Cows in the pLH36group were injected with porcine LH (Lutropin, 12.5 mg, im) at 24 h and inseminated at36 and 48 h after CIDR removal. Mean numbers of viable embryos were 7.8, 3.6 and9.6 for Control, Estradiol and pLH36 treatment groups, respectively (P > 0.10). In Trial2, multiparous beef cows (n = 22) were randomly allotted to one of three treatmentsfollowing superstimulation and removal of a CIDR. Sixteen of the cows weresuperstimulated a second time approximately 50 days later and allotted to one of the twotreatments that differed from the initial treatment group. Cows in the Control group wereinseminated at 12 and 24 h after onset of estrus. Cows in the two pLH groups were injected with porcine LH (Lutropin,12.5 mg, im) at 24 h after CIDR removal and wereinseminated with either one unit of semen at 36 and 48 h (pLH36) or with two units ofsemen at 48 h (pLH48) after CIDR removal. Mean numbers of viable embryos were 3.0,6.4 and 3.8 for Control, pLH36 and pLH48 treatment groups, respectively (P > 0.10).These data indicate that administration of pLH can facilitate use of fixed-time AI insuperovulated beef cows without sacrificing embryo production.The second study evaluated the efficacy of resynchronizing beef cow recipientsusing CIDR devices for only 7 or 14 d. Recipient cows received CIDRs either on theday of transfer (n = 88) or 7 d post-transfer (n = 230). All CIDRs were removed on d 21and cows were observed for estrus between d 22 and 24. Cows that displayed estruswere ultrasounded on d 30, those cows not pregnant that possessed a CL had an embryotransferred that day. Cows were later examined for pregnancies approximately 23 to 30d later. There were no differences in pregnancy rates between cows with 7 or 14 dCIDRs and therefore data were combined. Pregnancy rates at two different ranchesindicate that beef cow recipients can be successfully resynchronized by insertion of aCIDR without compromising pregnancy rates of transferred embryos. At Center Ranchthe pregnancy rate for the first transfer was 57% while the resynchronized group thatreceived the second transfer had a pregnancy rate of 55%. At Mound Creek Ranch thefirst transfer of embryos produced 59% pregnancy rates while the second transfer had apregnancy rate of 71%. No significant differences (P > 0.05) were observed between thepregnancy rates of the initial transfer and those of the resynchronized transfer using only CIDRs, indicating that resynchronization using CIDRs can be used without reducingpregnancy rates.