title: Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone.
abstract: We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F2alpha (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 microg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 microg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 microg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.
authors.affiliation: North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744, USA. clamb@umn.edu
authors.forename: G C
authors.initials: GC
authors.lastname: Lamb
authors.forename: J E
authors.initials: JE
authors.lastname: Larson
authors.forename: T W
authors.initials: TW
authors.lastname: Geary
authors.forename: J S
authors.initials: JS
authors.lastname: Stevenson
authors.forename: S K
authors.initials: SK
authors.lastname: Johnson
authors.forename: M L
authors.initials: ML
authors.lastname: Day
authors.forename: R P
authors.initials: RP
authors.lastname: Ansotegui
authors.forename: D J
authors.initials: DJ
authors.lastname: Kesler
authors.forename: J M
authors.initials: JM
authors.lastname: DeJarnette
authors.forename: D G
authors.initials: DG
authors.lastname: Landblom
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003692:Delayed-Action Preparations; D015237:Dinoprost / Q000008:administration & dosage / Q000494:pharmacology*; D004343:Drug Implants; D004971:Estrus / Q000187:drug effects*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000662:veterinary*; D008297:Male; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D015237:Dinoprost