title: Concentrations of luteinizing hormone and ovulatory responses in dairy cows before timed artificial insemination.
abstract: The objective was to determine the incidence of LH surges and ovulatory responses in lactating dairy cows enrolled in a timed artificial insemination (TAI) program. Cows were assigned randomly to 2 presynchronization treatments: (1) Pre10 (n=37): 2 injections of PGF2α (PG; PG-1 and PG-2) 14 d apart (Presynch); or (2) PG-3-G (n=33): one 25-mg injection of PG (Pre-PG) administered 3 d before a 100-µg GnRH injection (Pre-GnRH). Ten days after PG-2 or Pre-PG, all cows were enrolled in a 7-d Ovsynch TAI program [injection of GnRH (GnRH-1) 7 d before PG (PG-3) and GnRH (GnRH-2) administered at either 56 or 72 h after PG-3; TAI at 72 h]. Blood was collected to determine LH at (1) Pre-GnRH: 48 to 80 h after PG-2 and hourly from 72 to 78 h (Pre-GnRH at 72 h); (2) GnRH-1: 0 to 6 h after GnRH-1; and (3) GnRH-2: 48 to 80 h after PG-3 and hourly from 56 to 62 h or 72 to 78 h for cows injected with GnRH-2 at 56 or 72 h after PG-3, respectively. Ovaries were scanned and pregnancy per TAI (P/AI) was diagnosed 31 and 61 d post-TAI by transrectal ultrasonography. The Pre-GnRH injection increased the incidences of LH surges (100 vs. 43%) and ovulation (91 vs. 60%) and subsequent concentrations of progesterone in PG-3-G cows compared with Pre10 cows, respectively. Seven days later, incidence of ovulation (48 to 62%) and occurrence of LH surges (100%) did not differ between treatments after GnRH-1. In contrast, LH concentrations and area under the LH curve of Pre10 cows were greater than that of PG-3-G cows because progesterone was greater in PG-3-G than in Pre10 cows (4.6±0.4 vs. 2.8±0.4 ng/mL), respectively. Concentrations of LH did not differ after GnRH-2 at either 56 or 72 h; however, 1 cow receiving GnRH-2 at 56 h and 3 cows at 72 h had early spontaneous LH surges before GnRH-2. Ovulation was suppressed overall in 210 blood collection windows in cows with elevated progesterone concentrations. When progesterone was <1 ng/mL after either PG-2 or PG-3 injections, GnRH-induced LH surges occurred in more than 90% of cows, and incidence of ovulation exceeded 80%. Pregnancy per AI tended to differ for PG-3-G (56.7%) compared with Pre10 (37.8%) and for 56 h (54.5%) compared with 72 h (38.2%), with the Pre10-72 h treatment combination producing less than half (22.2%) the pregnancies compared with all other treatment combinations. Furthermore, in these same cows, post-TAI luteal tissue volume tended to be compromised. We conclude that incidences of GnRH-induced LH surges and ovulation are suppressed in cows with elevated progesterone, possibly contributing to some loss in P/AI in TAI programs.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201.
authors.forename: S L
authors.initials: SL
authors.lastname: Pulley
authors.affiliation: Division of Animal Sciences, University of Missouri, Columbia 65211.
authors.forename: D H
authors.initials: DH
authors.lastname: Keisler
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201. Electronic address: jss@k-state.edu.
authors.forename: J S
authors.initials: JS
authors.lastname: Stevenson
mesh_terms: D000818:Animals; D002417:Cattle; D015237:Dinoprost / Q000008:administration & dosage; D004973:Estrus Synchronization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007267:Injections; D007315:Insemination, Artificial / Q000662:veterinary*; D007986:Luteinizing Hormone / Q000097:blood*; D010053:Ovary / Q000187:drug effects* / Q000378:metabolism; D010060:Ovulation / Q000187:drug effects*; D011374:Progesterone / Q000097:blood
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone; D015237:Dinoprost
keywords: luteal function; luteinizing hormone; ovulation; presynchronization; progesterone