title: Pregnancy outcomes after change in dose delivery of prostaglandin F₂α and time of gonadotropin-releasing hormone injection in a 5-day timed artificial insemination program in lactating dairy cows.
abstract: We demonstrated that 50mg of PGF₂α on d 6 successfully induced luteolysis in lactating dairy cows enrolled in a traditional 5-d Ovsynch-72 program [GnRH injection 5 d before (d 0; GnRH-1) and 56 (p.m. on d 7; GnRH-2) or 72 h (d 8; GnRH-2) after a 25-mg injection of PGF₂α (d 5 and 6 after GnRH injection); timed artificial insemination (AI) on d 8]. Our current objective was to determine pregnancy outcomes in lactating dairy cows after a 50-mg injection of PGF₂α on d 6 or a 25-mg injection of PGF₂α on d 5 and 6 in a 5-d Ovsynch program. Cows in herd 1 diagnosed not pregnant between 30 and 36 d since last AI were enrolled to receive either a 50-mg injection of PGF₂α on d 6 (1 × 50; n=134) or a 25-mg injection of PGF₂α on d 5 and 6 (2 × 25; n=139) after GnRH-1 (d 0), with GnRH-2 at 72 h after PGF₂α injection (d 5), concurrent with timed AI (d 8). Cows in herd 2 diagnosed not pregnant between 34 and 40 d were treated similarly: even-tagged cows received the 2 × 25 (n=422) treatment, and odd-tagged cows received the 1 × 50 (n=450) treatment, except that GnRH-2 was administered at 56 h. Blood collected from cows in herd 1 at d 0, 5, 6, and 8 was assayed for progesterone. Luteolysis was defined to occur when progesterone concentration was ≥1 ng/mL on d 5, and 72 h later (d 8) was either <0.5 ng/mL or <1 ng/mL. Progesterone concentrations did not differ between treatments on pretreatment d 0 and 5, but were greater in 1 × 50 than 2 × 25 cows on d 6 (4.7 ± 0.2 vs. 1.1 ± 0.2 ng/mL) and d 8 (0.43 ± 0.04 vs. 0.19 ± 0.04 ng/mL), respectively. Luteolysis was greater in the 2 × 25 versus 1 × 50 treatment when the cut point was 0.5 ng/mL, whereas no difference was detected when the cut point was <1 ng/mL on d 8. Lack of complete luteolysis was greater in cows classified as early cycle on d 0 or having a new corpus luteum after d 0 because progesterone concentration was greater on d 5 and 6 than for cows classified as late cycle on d 0 or cows having low progesterone on d 0 and 5. Pregnancy per AI at 30 to 40 d did not differ between 2 × 25 and 1 × 50 cows having luteolysis by d 8 or in all cows (37.2 vs. 33.3%) in herd 1, respectively, but differed in herd 2 (24.7 vs. 19.5%; no treatment by herd interaction). We conclude that incomplete luteolysis by d 8 was greater in 1 × 50 cows using a cut point of <0.5 ng/mL at AI. The difference in pregnancy outcome in herd 2 may have resulted from insufficient time for complete luteolysis before GnRH-2 at 56 h compared with GnRH-2 at 72 h (at AI) in herd 1.
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
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: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201.
authors.forename: S L
authors.initials: SL
authors.lastname: Hill
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000187:drug effects; D036861:Delivery, Obstetric / Q000662:veterinary; D015237:Dinoprost / Q000008:administration & dosage*; D004973:Estrus Synchronization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation / Q000187:drug effects* / Q000502:physiology; D003341:Luteolysis / Q000187:drug effects; D011247:Pregnancy; D011256:Pregnancy Outcome; D011374:Progesterone / Q000097:blood; D013997:Time Factors
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D015237:Dinoprost
keywords: luteal tissue; luteolysis; ovulation; progesterone