188 Effect of Transfer of Frozen-Thawed Ivf Embryos on Pregnancy in Repeat-Breeder Inseminated or Non-Inseminated Holstein Cattle

Abstract

Repeat-breeding is one of the important factors that affect dairy management. The objective of this study was to investigate the effect of transfer of frozen–thawed IVF embryos on pregnancy in repeat-breeder Holstein cattle. Cumulus–oocyte complexes (COCs) were collected by aspiration of 2–1-mm follicles from ovaries obtained at a local abattoir. COCs were matured for 20 h in TCM-199 supplemented with 5% calf serum (CS) and 0.02 mg/mL of FSH at 38.5°C under a 5% CO2 atmosphere in air. Matured oocytes were inseminated with spermatozoa of 5 × 106/mL in BO solution (Brackett and Oliphant 1975 Biol. Reprod. 12, 260–274) containing 10 mM hypotaurine and 4 units/mL heparin. After 18 h of gamete co-culture, presumptive zygotes were cultured in CR1aa (Rosenkrans et al. 1991 Theriogenology 35, 266) supplemented with 5% CS for 8 days at 38.5°C under 5% CO2, 5% O2, 90% N2 atmosphere in air. After in vitro fertilization, Day 7 and Day 8 blastocysts were frozen in 1.5 M ethylene glycol (EG) in Dulbecco's PBS (DPBS) supplemented with 0.1 M sucrose and 20% CS. Embryos were transferred into a freezing medium, loaded into 0.25-mL straws, and allowed to stand for 15–20 min for equilibration. The straws were then plunged into a −7°C methanol bath of a programmable freezer for 1 min, seeded at −7°C, maintained at −7°C for 15 min, cooled to −30°C at the rate of −0.3°C/min, and then plunged into liquid nitrogen. Recipient animals (43 heifers, 131 cows) included those that did not conceive after being artificially inseminated (AI) 3 to 15 times. The frozen–thawed IVF embryos were directly transferred to the recipient animals 7 days after estrus or AI. Pregnancy rates were analyzed by chi-square test. The results are presented in Table 1. There were no significant differences in the pregnancy rates between treatments. However, a slightly higher pregnancy rate was achieved by embryo transfer after AI. These results suggest that embryo transfer may increase the pregnancy rate in repeat-breeder Holstein cattle. Table 1. Pregnancy rates after transfer of IVF frozen–thawed embryos in repeat-breeder Holstein cattle

A CIDR-Based Timed Embryo Transfer Protocol Increases the Pregnancy Rate of Lactating Repeat Breeder Dairy Cows

“…In addition, the pregnancy rate following TET in the present study was similar to that (48.9%) following ET in repeat breeder dairy cattle using frozen-thawed embryos collected from Japanese black cows [19]. Moreover, Dochi et al [18] demonstrated that ET using frozen-thawed in cows received TAI 30 h (Day 9) after the second EB injection in the CIDR-based TAI protocol. TET 3 : cows received TET using frozen-thawed blastocysts or morula embryos on Day 16 in the CIDR-based TET protocol.…”

“…Interestingly, embryo transfer (ET) can increase the probability of maintenance of pregnancy in lactating dairy cows by minimizing the negative effects of high milk production and heat stress on both the quality of the oocyte and early development of the embryo [17]. Similarly, this ET technique has been introduced as an efficient tool to improve fertility for repeat breeder dairy cattle [18,19]. It has also been reported that a progesterone (P4)-based timed ET (TET) protocol enables more recipients to be selected without a decrease in pregnancy rate compared with synchronization of estrus using PGF 2α [20].…”