title: Effects of postbreeding gonadotropin treatments on conception rates of lactating dairy cows subjected to timed artificial insemination or embryo transfer in a tropical environment.
abstract: The objective of experiment 1 was to evaluate the effects of treatments with human chorionic gonadotropin (hCG) or GnRH 7 d after induced ovulation on reproductive performance of lactating dairy cows submitted to timed artificial insemination (TAI) or timed embryo transfer (TET). A total of 834 potential breedings were used from 661 lactating Holstein cows (37.3±0.3 kg of milk/d). Cows had ovulation synchronized and were assigned randomly to receive TAI on d 0 or TET on d 7. Within each group, cows were assigned randomly to receive on d 7 no additional treatment (control; nTAI=156; nTET=126), a 100 μg i.m. injection of GnRH (nTAI=155; nTET=124), or a 2,500 IU i.m. injection of hCG (nTAI=151; nTET=122). Postbreeding treatment affected the percentages of pregnant cows at TET on d 28 (control: 38.1%; GnRH: 52.4%; hCG: 45.1%) and on d 60 (control: 32.5%; GnRH: 41.1%; hCG: 38.5%), but postbreeding treatment did not affect percentages of pregnant cows at TAI on d 28 (control: 30.1%; GnRH: 32.2%; hCG: 32.4%) or on d 60 (control: 25.6%; GnRH: 27.1%; hCG: 29.8%). The objective of experiment 2 was to evaluate the effect of a treatment with GnRH 7 d after TET on reproductive performance of lactating dairy cows that received a previous GnRH treatment at TET. A total of 285 potential breedings were used from 257 lactating Holstein cows (35.1±0.8 kg of milk/d). Cows had ovulation synchronized and were assigned for TET on d 7. Immediately after TET, all cows were treated with a 100 μg i.m. injection of GnRH. On d 14, cows were assigned randomly to receive (G7-14; n=147) or not (G7; n=138) an additional injection of GnRH. Pregnancy diagnosis were performed on d 28 and 60. The additional treatment with GnRH on d 14 did not affect the percentages of pregnant cows on d 28 (G7: 48.5%; G7-14: 42.9%) or on d 60 (G7: 39.8%; G7-14: 37.4%). In conclusion, treatment with GnRH or hCG 7 d after induced ovulation increased conception rates in lactating dairy cows submitted to TET, but not in cows submitted to TAI. Moreover, treatment with GnRH 7 d after TET did not enhance reproductive performance of lactating dairy cows that received a previous GnRH treatment at TET.
authors.affiliation: Departamento de Produção Animal, Faculdade de Medicina Veterinária e Zootecnia-UNESP, Botucatu-SP 18618-000, Brazil. vasconcelos@fmvz.unesp.br
authors.forename: J L M
authors.initials: JL
authors.lastname: Vasconcelos
authors.forename: O G
authors.initials: OG
authors.lastname: Sá Filho
authors.forename: P L T
authors.initials: PL
authors.lastname: Justolin
authors.forename: P
authors.initials: P
authors.lastname: Morelli
authors.forename: F L
authors.initials: FL
authors.lastname: Aragon
authors.forename: M B
authors.initials: MB
authors.lastname: Veras
authors.forename: S
authors.initials: S
authors.lastname: Soriano
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000494:pharmacology*; D004624:Embryo Transfer / Q000662:veterinary*; D005260:Female; D005306:Fertilization / Q000187:drug effects*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D011247:Pregnancy; D018873:Pregnancy Rate; D012102:Reproductive Control Agents / Q000008:administration & dosage / Q000494:pharmacology*; D014329:Tropical Climate
chemical_list: D006063:Chorionic Gonadotropin; D012102:Reproductive Control Agents