title: Conception rates after artificial insemination or embryo transfer in lactating dairy cows during summer in Florida.
abstract: The objective was to compare conception rates to embryo transfer relative to AI, during summer heat stress, in lactating dairy cows. Holstein cows (n = 180; 50 to 120 d postpartum) were allocated randomly to 1 of 3 groups: artificial insemination (AI, n = 84), embryo transfer using either embryos collected from superovulated donors (ET-DON, n = 48), or embryos produced in vitro (ET-IVF, n = 48). Embryos from superovulated donors were frozen in 10% glycerol and were rehydrated in a 3-step procedure, in decreasing concentrations of glycerol in a sucrose medium before transfer. Embryos produced in vitro were frozen in 1.5 M ethylene glycol, thawed and transferred without rehydration. Blood samples were collected from AI and ET recipients on Days 0, 7 and 22 for measurement of progesterone in plasma. Conception rate was estimated for the three groups at Day 22 (progesterone > 1 ng/mL) and confirmed at Day 42 by palpation per rectum. Conception rate estimates at Day 22 did not differ among groups (AI, 60.7%; ET-DON, 60.4%; ET-IVF, 54.2%), but conception rates at Day 42 differed (AI, 21.4%; ET-DON, 35.4%; ET-IVF, 18.8%; AI versus ET: P > 0.10 and ET-DON versus ET-IVF: P < 0.05). In cows considered pregnant at 22 d but diagnosed open at 42 d, the interestrous intervals were 28.8 +/- 2.2, 35.2 +/- 3.5 and 31.6 +/- 2.9 d, respectively, for AI, ET-DON and ET-IVF groups. Transfer of embryos collected from nonheat-stressed superovulated donors significantly increased conception rates in heat stressed dairy cattle. However, transfer of IVF-derived embryos had no advantage over AI. Where appropriate mechanisms are in place to attenuate the effects of heat stress, embryo transfer using frozen-thawed donor embryos increases conception rates.
authors.affiliation: Department of Large Animal Clinical Sciences, University of Florida, Gainesville 32611, USA.
authors.forename: M
authors.initials: M
authors.lastname: Drost
authors.forename: J D
authors.initials: JD
authors.lastname: Ambrose
authors.forename: M J
authors.initials: MJ
authors.lastname: Thatcher
authors.forename: C K
authors.initials: CK
authors.lastname: Cantrell
authors.forename: K E
authors.initials: KE
authors.lastname: Wolfsdorf
authors.forename: J F
authors.initials: JF
authors.lastname: Hasler
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
mesh_terms: D000818:Animals; D002417:Cattle; D015925:Cryopreservation; D004624:Embryo Transfer / Q000706:statistics & numerical data / Q000662:veterinary*; D005314:Embryonic and Fetal Development; D005260:Female; D005306:Fertilization; D005313:Fetal Death / Q000662:veterinary; D005431:Florida; D007315:Insemination, Artificial / Q000706:statistics & numerical data / Q000662:veterinary*; D007774:Lactation; D011247:Pregnancy; D012621:Seasons; D013480:Superovulation