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In ruminants, uterine pulses of prostaglandin (PG) F2α characterize luteolysis, while increased PGE2/PGE1 distinguish early pregnancy. This study evaluated intrauterine (IU) infusions of PGF2α and PGE1 pulses on corpus luteum (CL) function and gene expression. Cows on day 10 of estrous cycle received 4 IU infusions (every 6 h; n = 5/treatment) of saline, PGE1 (2 mg PGE1), PGF2α (0.25 mg PGF2α), or PGE1 + PGF2α. A luteal biopsy was collected at 30 min after third infusion for determination of gene expression by RNA-Seq. As expected, IU pulses of PGF2α decreased (P < 0.01) P4 luteal volume. However, there were no differences in circulating P4 or luteal volume between saline, PGE1, and PGE1 + PGF2α, indicating inhibition of PGF2α-induced luteolysis by IU pulses of PGE1. After third pulse of PGF2α, luteal expression of 955 genes were altered (false discovery rate [FDR] < 0.01), representing both typical and novel luteolytic transcriptomic changes. Surprisingly, after third pulse of PGE1 or PGE1 + PGF2α, there were no significant changes in luteal gene expression (FDR > 0.10) compared to saline cows. Increased circulating concentrations of the metabolite of PGF2α (PGFM; after PGF2α and PGE1 + PGF2α) and the metabolite PGE (PGEM; after PGE1 and PGE1 + PGF2α) demonstrated that PGF2α and PGE1 are entering bloodstream after IU infusions. Thus, IU pulses of PGF2α and PGE1 allow determination of changes in luteal gene expression that could be relevant to understanding luteolysis and pregnancy. Unexpectedly, by third pulse of PGE1, there is complete blockade of either PGF2α transport to the CL or PGF2α action by PGE1 resulting in complete inhibition of transcriptomic changes following IU PGF2α pulses.

This study evaluated the influence of GnRH analogs (gonadorelin vs. buserelin) and doses (single vs. double) on LH release and ovulatory response in Bos indicus (Nelore) females on Day 7 of the estrous cycle. Cycling heifers and non-lactating cows were pre-synchronized: Day −10: progesterone (P4) implant insertion plus 2 mg of estradiol benzoate; Day −2: implant removal and 0.53 mg of cloprostenol sodium (PGF); Day 0: 25 μg of lecirelin (GnRH). Over four replicates, heifers (n = 57) and cows (n = 53) that ovulated to the GnRH treatment on Day 0, having a visible corpus luteum (CL) and a dominant follicle (DF) ≥ 8.5 mm, were allocated to receive the following GnRH treatments on Day 7: G-Single (100 μg of gonadorelin); G-Double (200 μg of gonadorelin); B-Single (10 μg of buserelin); and B-Double (20 μg of buserelin). At GnRH treatment, a P4 implant was inserted in heifers (0.5 g) and cows (1 g). Ultrasound examinations were done on Days −10, −2, 0, 2, 7, 9, 12, and 14 to evaluate DF diameter, ovulation and presence of CL. Blood samples were collected on Day 7 at 0, 2, and 4 h from GnRH treatment, to evaluate circulating P4 and LH concentrations. On Day 12, the P4 implant was removed, females received two PGF treatments (24 h apart), and 2 d later, 25 μg of GnRH was given to start the next replicate. In both heifers and cows, P4 concentrations were elevated on Day 7, and similar among groups (3.9 and 4.2 ng/mL, respectively). In heifers, buserelin induced greater LH peak (9.5 vs. 2.6 ng/mL; P < 0.01) and greater ovulation (88.9 [24/27] vs. 16.7% [5/30]; P < 0.01) than gonadorelin treatments, regardless of the dose. Similarly, in cows, buserelin induced greater LH peak than gonadorelin (9.9 vs. 4.9 ng/mL; P < 0.01). However, ovulation was only increased in cows from the B-Double group (90.9% [10/11]), whereas in the other groups the ovulatory response was similar (35.7% [15/42]). Regardless of treatment, heifers had similar P4 concentrations (P = 0.22), but smaller DF (P < 0.01) than cows on Day 7. Only in G-Double group the LH peak was lower (P = 0.05) in heifers than in cows, with no difference within other groups. In heifers, but not in cows, the single dose of buserelin resulted in high ovulatory response, equivalent to that produced by the double dose. In conclusion, in Bos indicus heifers and cows on Day 7 of the cycle, with elevated P4 concentrations, buserelin induced greater LH release and ovulatory response than gonadorelin treatments. Double doses increased the LH release, however, only resulted in greater ovulation in females treated with buserelin. Finally, although circulating P4 concentrations did not differ between parities, heifers were more likely to ovulate in response to a GnRH-induced LH peak than cows. • Buserelin induced greater LH release and ovulation than gonadorelin in Bos indicus. • Double doses increased LH release, but only double buserelin increased ovulation. • In heifers, but not cows, the single dose of buserelin resulted in high ovulation. • Heifers had similar circulating P4 but smaller dominant follicles than cows. • Heifers were more likely to ovulate after a GnRH-induced LH peak than cows. [ABSTRACT FROM AUTHOR]

Inappropriate corpus luteum (CL) regression can produce pregnancy loss. An experimental model was utilized to investigate regression of accessory CL during pregnancy in dairy cows. Cows were bred (day 0) and treated with gonadotrophin-releasing hormone 6 days later to form accessory CL. Transrectal ultrasound (every other days) and blood samples for progesterone (P4; daily) were performed until day 56 of pregnancy. On day 28, 13 cows were confirmed pregnant, and accessory CL were found contralateral (n = 9) or ipsilateral (n = 4) to previous ovulation. On day 18, CL biopsy was performed to analyze mRNA expression for interferonstimulated genes (ISGs). Luteolysis occurred more frequently in cows that had contralateral accessory CL (88.9% (8/9)) than in cows with ipsilateral accessory CL (0% (0/4)). Luteolysis of contralateral accessory CL occurred either earlier (days 19-23; 2/8) or later (days 48-53; 6/8) in pregnancy and occurred rapidly (24 h), based on daily P4. After onset of earlier or later accessory CL regression, circulating P4 decreased by 41.2%. There was no difference in luteal tissue mRNA expression for ISGs on day 18 between accessory and original CL and between CL that subsequently regressed or did not regress. On day 56, an oxytocin challenge dramatically increased prostaglandin F2a metabolite (PGFM) in all cows but produced no pregnancy losses, although cows with previous accessory CL regression had greater PGFM. In summary, ipsilateral accessory CL did not regress during pregnancy, whereas most contralateral CL regressed by 63 days of pregnancy, providing evidence for local mechanisms in regression of accessory CL and protection of CL during pregnancy. [ABSTRACT FROM AUTHOR]

The 5-day CO-Synch is an extensively used TAI protocol; however, it requires multiple administrations of prostaglandin F2a (PGF). The objective of the present study was to evaluate the effect of increasing progesterone (P4) device insertion from 5 to 6 days during a TAI protocol on ovarian dynamics and fertility in beef cows. Suckled beef cows (n = 867) at six locations were randomly assigned to either a 5-day or 6-day CO-Synch. Cows received an intravaginal P4 device (CIDR, Zoetis) and 100 µg of gonadorelin acetate (GnRH, Parnell) on d-9 (6-day) or d-8 (5-day). On d-3 CIDR's were removed, an estrus detection patch applied (Estrotect, Rockway Inc.) and either one (6-day) or two (5-day) doses of PGF (500 µg of cloprostenol sodium, Estroplan, Parnell) was administered. On d0 (72 h after CIDR removal) all cows received 100 µg of GnRH, estrus expression was evaluated, and AI was performed. Pregnancy was determined by ultrasonography 34 days after TAI. Ovarian dynamics were evaluated in a subset of animals (n = 20) between d-3 and d7 to determine preovulatory follicle size, time of ovulation and corpus luteum (CL) size. Data were analyzed using generalized linear mixed models (SAS 9.4). Cows in the 6-day group tended (P = 0.09) to have a larger maximum follicle diameter (16.2±0.4mm) than cows in the 5-day group (15.0±0.6mm). In addition, CL volume on d7 was greater (P = 0.01) in the 6-day (4302±495mm3) than 5-day (2406±455mm3) group. There were, however, no differences (P = 0.15) in the interval between CIDR removal and ovulation. Cows assigned to the 6-day group had greater (P < 0.05) estrus expression [56.1% (215/385) vs 41.5% (161/388)] and pregnancy rate [54.6% (236/438) vs 47.4% (207/435)] than cows in the 5-day group. In conclusion, extension of the period of P4 device insertion in a prolonged proestrus protocol increases preovulatory follicle size, estrous expression, and fertility to TAI. [ABSTRACT FROM AUTHOR]