title: Efficacy of embryo transfer in lactating dairy cows during summer using fresh or vitrified embryos produced in vitro with sex-sorted semen.
abstract: The objective was to determine whether transfer of fresh or vitrified embryos produced in vitro with sex-sorted semen improves pregnancy and calving rates during summer in lactating dairy cows compared with artificial insemination (AI). Lactating dairy cows (n=722) were enrolled during summer months at 2 commercial dairies in Central Texas and randomly assigned to 1 of 3 treatments: AI with conventional semen (n=227), embryo transfer-vitrified (ET-V; n=279) or embryo transfer-fresh (ET-F; n=216). Embryos were produced in vitro using sex-sorted semen and with Block-Bonilla-Hansen-7 culture medium. For vitrification, grade 1 expanded blastocysts were harvested on d 7 after fertilization and vitrified using the open-pulled straw method. Fresh embryos were grade 1 blastocysts and expanded blastocysts harvested on d 7 after fertilization. Cows were submitted to the Ovsynch56 protocol: d -10 GnRH, d -3 PGF(2α), d -1 GnRH and d 0 timed AI; or Select Synch protocol: d -9 GnRH, d -2 PGF(2α), and AI following detected estrus (day of AI=d 0). On d 7, all cows were examined for presence of a corpus luteum (CL). A vitrified or fresh embryo was transferred to cows with CL in ET-V and ET-F groups. Cows were considered synchronized if progesterone was <1ng/mL on d 0 and a CL was present on d 7. At d 40±7 of gestation, the percentage of cows pregnant was greater for the ET-F compared with the ET-V and AI groups among all cows (42.1 vs. 29.3 and 18.3%, respectively) and synchronized cows (45.5 vs. 31.6 and 24.8%, respectively). Also, the percentage of cows pregnant was greater for the ET-V than the AI group among all cows and tended to be greater among synchronized cows. At d 97±7 of gestation, the percentage of cows pregnant among all cows was greater for ET-F and ET-V groups than for the AI group (36.4 and 25.7 vs. 17.0%, respectively) and the percentage for the ET-F group was greater than for the ET-V group. Among synchronized cows, the percentage of cows pregnant was significantly increased for the ET-F group than for ET-V and AI groups (39.4 vs. 27.8 and 23.1%, respectively) and no difference was found between ET-V and AI groups. No effect of treatment on embryo loss was observed. The percentage of cows with live births was significantly increased for the ET-F than for ET-V and AI groups among all cows (27.5 vs. 17.1 and 14.6%, respectively) and synchronized cows (29.9 vs. 18.5 and 20.0%, respectively). The percentage of cows giving birth to a live heifer was significantly increased for the ET-F and ET-V groups compared with the AI group among all cows (79.1 and 72.5 vs. 50.0%, respectively) and synchronized cows (79.1 and 72.5 vs. 50.0%, respectively). No difference existed between ET-F and ET-V groups for percent live heifer births but both were greater than for the AI group. The transfer of fresh embryos produced in vitro using sex-sorted semen to lactating dairy cows during summer can effectively increase the percentage of cows that establish pregnancy and also the percentage of cows that give birth to a live heifer compared with percentages from AI with conventional semen.
authors.affiliation: Texas AgriLife Research and Extension, Texas A&M System, Stephenville, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Stewart
authors.forename: J
authors.initials: J
authors.lastname: Block
authors.forename: P
authors.initials: P
authors.lastname: Morelli
authors.forename: A E
authors.initials: AE
authors.lastname: Navarette
authors.forename: M
authors.initials: M
authors.lastname: Amstalden
authors.forename: L
authors.initials: L
authors.lastname: Bonilla
authors.forename: P J
authors.initials: PJ
authors.lastname: Hansen
authors.forename: T R
authors.initials: TR
authors.lastname: Bilby
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004624:Embryo Transfer / Q000379:methods / Q000662:veterinary*; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary; D007774:Lactation; D011247:Pregnancy; D018873:Pregnancy Rate; D012621:Seasons; D012661:Semen / Q000166:cytology*; D012743:Sex Preselection / Q000662:veterinary*; D013781:Texas