title: Effect of interval to resynchronization of ovulation on fertility of lactating Holstein cows when using transrectal ultrasonography or a pregnancy-associated glycoprotein enzyme-linked immunosorbent assay to diagnose pregnancy status.
abstract: The objective of this study was to compare 2 strategies for resynchronization of ovulation based on nonpregnant diagnoses using transrectal ultrasonography or a pregnancy-associated glycoprotein (PAG) ELISA. Lactating Holstein cows (n = 1,038) were submitted for first postpartum timed artificial insemination (TAI) using a Presynch + Ovsynch protocol. After the initial breeding, cows were randomly assigned to initiate resynchronization 25 d (D25) or 32 d (D32) later. Pregnancy status of cows initiating Resynch 25 d after TAI was determined 27 d after TAI by using a PAG ELISA, whereas pregnancy status of cows initiating Resynch 32 d after TAI was determined 39 d after TAI using transrectal ultrasonography. Cows diagnosed as not pregnant continued the Resynch protocol by receiving an injection of PGF(2 alpha) 7 d after the initial GnRH injection and a second GnRH injection 54 h after the PGF(2 alpha) injection. Cows in both treatments were inseminated approximately 16 h after the second GnRH injection. Blood samples for analysis of progesterone (P(4)) were collected at the first GnRH injection of each Resynch protocol. Pregnancies per AI (P/AI) of nonpregnant cows initiating Resynch 25 vs. 32 d after first postpartum TAI did not differ 39 d after TAI and were 28.3 vs. 30.9% for D25 vs. D32 cows, respectively. Mean P(4) at the first GnRH injection of Resynch was greater for D32 than for D25 cows (3.67 +/- 0.22 vs. 2.83 +/- 0.22 ng/mL), indicating that the Resynch treatments were initiated at different stages of the estrous cycle. After blocking P(4) concentration into low (<1.0 ng/mL) or high (>or=1.0 ng/mL) classes, P(4) class was not found to affect P/AI 39 d after TAI. Early resynchronization was not found to affect P/AI 39 d after TAI; however, early resynchronization did decrease days between inseminations and the interval from the initial nonpregnant diagnosis to conception. Earlier detection of nonpregnant cows using the PAG ELISA in conjunction with a TAI resynchronization program may improve the rate at which cows become pregnant in a dairy herd compared with transrectal ultrasonography conducted at a later stage after TAI.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: E
authors.initials: E
authors.lastname: Silva
authors.forename: R A
authors.initials: RA
authors.lastname: Sterry
authors.forename: D
authors.initials: D
authors.lastname: Kolb
authors.forename: N
authors.initials: N
authors.lastname: Mathialagan
authors.forename: M F
authors.initials: MF
authors.lastname: McGrath
authors.forename: J M
authors.initials: JM
authors.lastname: Ballam
authors.forename: P M
authors.initials: PM
authors.lastname: Fricke
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards / Q000662:veterinary*; D005260:Female; D005298:Fertility / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000379:methods / Q000592:standards / Q000662:veterinary*; D007774:Lactation / Q000502:physiology; D010060:Ovulation / Q000502:physiology*; D011247:Pregnancy; D011258:Pregnancy Tests / Q000379:methods / Q000592:standards / Q000662:veterinary*; D011374:Progesterone / Q000097:blood; D011897:Random Allocation; D013997:Time Factors; D014463:Ultrasonography / Q000592:standards / Q000662:veterinary*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone