title: Low progesterone concentration during the development of the first follicular wave reduces pregnancy per insemination of lactating dairy cows.
abstract: Objectives were to determine the effect of progesterone (P4) concentration on fertility of lactating dairy cows induced to ovulate follicles of the first follicular wave. Lactating dairy cows (n=989) at 38±3d postpartum were balanced by parity and body condition score and randomly assigned to 3 treatments: first follicular wave (FFW), first follicular wave with exogenous P4 (FFWP), or second follicular wave (SFW). All cows had their estrous cycle presynchronized with 2 injections of prostaglandin (PG) F(2α) given 14 d apart. Cows in the FFW and FFWP treatments started the ovulation synchronization protocol 3 d after the last PGF(2α) of the presynchronization protocol, whereas SFW cows received a GnRH injection (100 μg of gonadorelin diacetate; Cystorelin, Merial Ltd., Duluth, GA) 3 d after the last PGF(2α) of the presynchronization protocol and started the synchronization protocol 7 d later. The synchronization protocol consisted of GnRH on d -10, PGF(2α) on d -3, and GnRH concurrent with timed artificial insemination (AI) on d 0. Cows in the FFWP treatment received 2 controlled internal drug release inserts containing 1.38 g of P4 from d -8 to -3. Progesterone concentration was determined on d -10, -8, -6, -3, and 0 from all cows and at 7, 14, and 21 d after AI from a subsample of cows (n=170). Cows (n=715) had their ovaries scanned by ultrasound on d -10, -3, and 7 d. Pregnancy was diagnosed at 38 and 66 d after AI. Concentration of P4 from study d -8 to -3 was lowest for FFW cows (1.4±0.1 ng/mL) and similar between SFW (3.7±0.2 ng/mL) and FFWP (3.7±0.1 ng/mL) cows. Diameter of the dominant follicle on study d -3 was greater for FFW cows (16.5±0.3 mm) than for SFW cows (15.4±0.3 mm), but diameter of the dominant follicle of FFWP cows was not different (15.9±0.3 mm) compared with that of SFW and FFW cows. The incidence of multiple ovulation was largest for FFW cows (SFW=19.5, FFW=33.6, FFWP=19.0%), but pregnancy per AI (P/AI) at 66 d was smallest for FFW cows (SFW=38.9, FFW=22.3, FFWP=32.0%). Anovular cows in the SFW (19.4 vs. 42.8%) and FFWP (22.1 vs. 37.2%) treatments had reduced P/AI compared with cyclic cows, despite having similar or greater P4 concentration from study d -8 to -3, respectively. Estrus and ovulation synchronization protocols for lactating dairy cows must result in growth of ovulatory follicle under P4 concentration >2 ng/mL to ensure high P/AI.
authors.affiliation: School of Veterinary Medicine, University of California-Davis, Tulare 93274, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Denicol
authors.forename: G
authors.initials: G
authors.lastname: Lopes
authors.forename: L G D
authors.initials: LG
authors.lastname: Mendonça
authors.forename: F A
authors.initials: FA
authors.lastname: Rivera
authors.forename: F
authors.initials: F
authors.lastname: Guagnini
authors.forename: R V
authors.initials: RV
authors.lastname: Perez
authors.forename: J R
authors.initials: JR
authors.lastname: Lima
authors.forename: R G S
authors.initials: RG
authors.lastname: Bruno
authors.forename: J E P
authors.initials: JE
authors.lastname: Santos
authors.forename: R C
authors.initials: RC
authors.lastname: Chebel
mesh_terms: D000034:Abortion, Veterinary / Q000453:epidemiology; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004973:Estrus Synchronization; D005260:Female; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation / Q000502:physiology*; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D010062:Ovulation Induction / Q000662:veterinary; D011247:Pregnancy; D011374:Progesterone / Q000097:blood*; D014463:Ultrasonography
chemical_list: D011374:Progesterone