title: Short communication: Insertion of an intravaginal progesterone device at the time of gonadotropin-releasing hormone (GnRH) injection affects neither GnRH-induced release of luteinizing hormone nor development of dominant follicle in early diestrus of lactating dairy cows.
abstract: Our objectives were to evaluate the acute effects of a controlled internal drug release (CIDR) insert containing 1.38 g of progesterone (P4) on the release of LH, follicular growth, and circulating concentrations of P4 in cows treated with GnRH at the time of CIDR insertion. Nonpregnant, lactating dairy cows (n=27) were blocked by parity, predicted 305-d mature-equivalent milk production, and body condition score and randomly assigned to 1 of 3 treatments: (1) CIDR insertion concurrent with an injection of 200 µg of GnRH (n=10; 2GP4); (2) CIDR insertion concurrent with an injection of 100 µg of GnRH (n=10; 1GP4); and (3) injection of 100 µg of GnRH (n=7; CON). Prior to onset of treatments, cows were submitted to a presynchronization protocol that consisted of a CIDR insert containing 1.38 g of P4 from d -7 to -2, 25mg of PGF2α on d -2 and -1, and 100 µg of GnRH on d 0. Experimental treatments were applied on d 6, the early luteal phase of the estrous cycle. Concentrations of P4 in plasma were determined on d -2 and 0 and at 0, 15, 30, 60, 120, 240, 345, 600, and 1,200 min relative to treatment on d 6. Concentrations of LH were determined in plasma samples obtained at 0, 15, 30, 60, 120, 240, and 345 min relative to treatment on d 6. Ultrasonography examinations of ovarian structures were performed on d -2, 0, 2, and at 0, 600, and 1,200 min relative to treatment on d 6. Mean concentrations of P4 in the CON group (1.91±0.28 ng/mL) were lower than in 2GP4 (3.40±0.26 ng/mL) and 1GP4 (3.31±0.24 ng/mL) groups, but concentrations in 2GP4 and 1GP4 were similar. Mean concentration of LH in response to the GnRH injection on d 6 was greatest in 2GP4 cows (3.08±0.21 ng/mL) and did not differ between 1GP4 (2.23±0.21 ng/mL) and CON (2.14±0.25 ng/mL) cows. The diameter of the dominant follicle on d 6 was similar among treatments (2GP4=15.34±0.50; 1GP4=15.31±0.50; CON=14.77±0.62 mm). In conclusion, CIDR insertion concurrent with a 100- or 200-µg dose of GnRH neither altered GnRH-induced LH release nor had an acute effect on dominant follicle growth.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506; Department of Veterinary Population Medicine, University of Minnesota, Saint Paul 55108. Electronic address: mendonca@k-state.edu.
authors.forename: L G D
authors.initials: LG
authors.lastname: Mendonça
authors.affiliation: Department of Animal Science, Texas A&M University, College Station 77843.
authors.forename: M
authors.initials: M
authors.lastname: Amstalden
authors.affiliation: Department of Veterinary Population Medicine, University of Minnesota, Saint Paul 55108.
authors.forename: R C
authors.initials: RC
authors.lastname: Chebel
mesh_terms: D000282:Administration, Intravaginal; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003692:Delayed-Action Preparations; D015237:Dinoprost / Q000008:administration & dosage; D030762:Estrous Cycle / Q000187:drug effects; D004973:Estrus Synchronization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007774:Lactation; D007986:Luteinizing Hormone / Q000097:blood*; D006080:Ovarian Follicle / Q000187:drug effects; D010053:Ovary / Q000000981:diagnostic imaging; D010298:Parity; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage*; D011897:Random Allocation
chemical_list: D003692:Delayed-Action Preparations; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone; D015237:Dinoprost
keywords: controlled internal drug release insert; dairy cow; exogenous progesterone; luteinizing hormone