title: Increased cleavage and blastocyst rate in ewes treated with bovine somatotropin 5 days before the end of progestin-based estrous synchronization.
abstract: Treatment with bovine somatotropin (bST) during estrous synchronization increased fertility and prolificacy in sheep. In the present study, a single dose of bST 5 days before the end of progestin treatment improved cleavage and embryo development. Stage of estrous cycle was synchronized in ewes (n=32) with progestin and superovulation was induced by use of FSH. Five days before the end of progestin treatment, ewes were randomly assigned to two groups: bST group (n=16) received a depot injection of 125 mg of bST sc (Lactotropina, Elanco, México) and the control group (n=16) received saline solution. Estrous was detected with rams fitted with an apron every 2 h and estrous sheep were mated every 8 h whilst in estrous. Embryos were recovered on Day 7 post mating, assessed microscopically and fixed in 4% paraformaldehyde. Cell number in blastocysts was counted after Hoechst 33342 staining. Plasma concentrations of IGF-I, insulin and progesterone were determined in eight sheep per group from the day of bST treatment to the day of embryo recovery. Cleavage rate, percentage of transferable embryos (transferable embryos/cleaved) and percentage of embryos reaching the blastocyst stage (blastocyst/cleaved) were compared between groups by logistic regression. IGF-I, insulin and progesterone plasma concentrations were analyzed by ANOVA for repeated measurements and cell number by ANOVA. Cleavage rate was greater (P<0.01) in bST treatment group (86%) than in the control group (62%). Similarly, the proportion of embryos reaching the blastocyst stage (bST=68.7 vs control=42.5) and the number of cells per blastocyst (bST group 91.8±5.5 compared to control group 75±6) were greater (P<0.01) in the bST-treated sheep. Plasma concentrations of IGF-I and insulin were greater (P<0.01) in the bST-treated group. No changes were observed in progesterone concentrations (P=0.5). It is concluded that bST injection 5 days before progestin removal increases cleavage rate and the proportion of embryos that reach the blastocyst stage. These effects are associated with an increase in IGF-I and insulin concentrations.
authors.affiliation: Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, Av. Universidad 3000, 04510 México DF, Mexico.
authors.forename: A
authors.initials: A
authors.lastname: Montero-Pardo
authors.forename: J
authors.initials: J
authors.lastname: Hernández-Cerón
authors.forename: S
authors.initials: S
authors.lastname: Rojas-Maya
authors.forename: J
authors.initials: J
authors.lastname: Valencia
authors.forename: A
authors.initials: A
authors.lastname: Rodríguez-Cortez
authors.forename: C G
authors.initials: CG
authors.lastname: Gutiérrez
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000187:drug effects* / Q000502:physiology; D047108:Embryonic Development / Q000187:drug effects* / Q000502:physiology; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D016015:Logistic Models; D008297:Male; D008856:Microscopy, Fluorescence / Q000662:veterinary; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D011897:Random Allocation; D012756:Sheep / Q000097:blood / Q000502:physiology*
chemical_list: D007328:Insulin; C073294:growth hormone, bovine; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone