The pathophysiology underlying follicular cysts appears to be lack of an estradiol (E2)-induced GnRH/LH surge due to hypothalamic insensitivity to E2. In addition, progesterone (P4) can cause animals with follicular cysts to resume normal cyclicity and normal hypothalamic responsiveness to E2. We postulated that follicular cysts may be a pathological manifestation of a physiological state that cows, and possibly other species, go through during the normal estrous cycle but the rise in P4 following ovulation induces them back to normal hypothalamic responsiveness to E2. Based on this hypothesis, we expected that removal of the ovary containing the corpus hemorrhagicum would prevent the normal rise in P4 following ovulation and induce development of follicular cysts. Cows (n = 24) on day 7 of the estrous cycle were treated with prostaglandin F2agr; (PGF2agr;) and time of ovulation was detected by ovarian ultrasonography every 8 h. Immediately following detection of ovulation, cows were randomly but unequally assigned to have the ovary containing the corpus hemorrhagicum removed (TRT; n = 16) or the ovary opposite to the corpus hemorrhagicum removed (CON; n = 8). Cows were subsequently evaluated by daily ultrasound and blood sampling to determine follicular dynamics. Ovulation was detected at 93.7 ± 4.5 h after PGF2agr; injection. All CON cows had a normal estrous cycle length (22.0 ± 0.6 days) after ovariectomy (OVX). Half of the TRT cows became anovular (TRT-ANO; n = 8) after OVX with large anovular follicles developing on the ovary (maximal size, 25.4 ± 1.4 mm; range, 20–32 mm). However, eight TRT cows ovulated (TRT-OV; n = 8) 7.3 ± 0.6 days after OVX. Control cows had a normal P4 rise after ovulation. Removal of the newly formed corpus hemorrhagicum prevented the rise in circulating serum P4 in TRT-ANO cows throughout the 25-day experimental period. The TRT-OV cows had a delayed increase in circulating P4 but it was normal in relation to time of ovulation. Serum E2 concentrations were similar among groups (TRT-OV, TRT-ANO and CON cows) until 7 days after OVX. Serum E2 concentrations then decreased in TRT-OV and CON cows but remained elevated (>5 pg/ml) in TRT-ANO cows. Thus, the endogenous increase in circulating E2 that induces the GnRH/LH surge and estrus is sufficient to induce cows into a physiological state that resembles follicular cysts if it is not followed by increased circulating P4.
Ahmet Gümen and Milo C Wiltbank
Rafael R Domingues, O J Ginther, Mateus Z Toledo, and Milo C Wiltbank
Understanding the impacts of nutrition on reproductive physiology in cattle are fundamental to improve reproductive efficiency for animals under different nutritional conditions. Starting on Day 0 (day of ovulation) until next ovulation, Holstein heifers (n = 24) were fed: low energy diet (ad libitum grass hay; LED) and high energy diet (ad libitum grass hay + concentrate supplement; HED). Heifers on HED gained more weight (average daily gain: 0.824 ± 0.07 vs 0.598 ± 0.09 kg/day) and had increased insulin concentrations. The dominant follicle of wave 1 in HED had greater growth rate overall from Days 0 to 8 and on Days 6–7 and 8–9 and started atresia later. The dominant follicle of wave 2 in HED had greater growth rate overall from Day 9 to 18 and on Days 14–15 and 15–16. In two-wave patterns, there was no difference in estradiol or progesterone concentrations but concentrations of FSH were lower in HED on Days 15 and 16. Estradiol concentrations increased earlier in two-wave patterns in association with earlier luteolysis. The frequency of two follicular waves was greater in HED than LED (11/12 vs 6/11; 92.7% vs 54.5%). In conclusion, an acute increase in dietary energy altered not only growth rate of the dominant follicle but also follicular wave pattern in heifers by increasing frequency of two follicular waves. The hypotheses were supported that an acute increase in dietary energy (1) prolongs growth period of dominant follicles and (2) alters follicular wave pattern in heifers.
Victor E Gomez-León, O J Ginther, Rafael R Domingues, José D Guimarães, and Milo C Wiltbank
Previous research demonstrated that acute treatment with GnRH antagonist, Acyline, allowed follicle growth until ~8.5 mm and no dominant follicle was selected. This study evaluated whether deficient LH was the underlying mechanism for Acyline effects by replacing LH action, using human chorionic gonadotropin (hCG), during Acyline treatment. Holstein heifers (n = 24) during first follicular wave were evaluated by ultrasound and randomized into one of three treatments: Control (saline treatments), Acyline (5 µg/kg Acyline), or Acyline+hCG (Acyline plus 50 IU of hCG at start then 100 IU every 12 h). Pulses of LH were present in Control heifers (9 Pulses/10 h) but not during Acyline treatment. Data were normalized to the transition to diameter deviation (day 0; F1 ~7.5 mm). Diameter deviation of the largest (F1) and the second largest (F2) follicle was not observed in Acyline-treated heifers, whereas control heifers had decreased growth of F2 at F1 ~7.5 mm, indicating deviation. Selection of a single dominant follicle was restored by providing LH activity in Acyline+hCG heifers, as evidenced by F1 and F2 deviation, continued growth of F1, and elevated circulating estradiol. Separation of F1 and F2 occurred 12 h (~7.0 mm) earlier in Acyline+hCG heifers than Controls. Circulating FSH was greater in Acyline than Controls, but lower in Acyline+hCG than Controls after day 1.5. In conclusion, dominant follicle selection and growth after follicle deviation is due to LH action as shown by inhibition of this process during ablation of GnRH-stimulated LH pulses with Acyline and restoration of it after replacement of LH action by hCG treatment.
Pedro L J Monteiro, Roberto Sartori, Aurea M O Canavessi, Leonardo F Melo, Jessica C L Motta, Carlos E C Consentini, and Milo C Wiltbank
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 interferon-stimulated 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 F2α 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.
Pedro L J Monteiro, Caio A Gamarra, Rodrigo S Genari, Alexandre B Prata, Rafael V Barletta, Peregrino G Duran, Aurea M O Canavessi, Roberto Sartori, and Milo C Wiltbank
The objective of this study was to evaluate the effect of accessory corpus luteum (CL) induction on fertility in dairy cows. On day 5 after artificial insemination (AI), lactating Holstein cows were assigned unequally to receive gonadotrophin-releasing hormone treatment (GnRH) (n = 641) or no treatment (control; n = 289). Cows had their blood sampled for progesterone (P4), and ovaries were scanned by ultrasound on days 5, 12, 19, 26, 33, 47, and 61 after AI. Pregnancy diagnosis was performed on days 26, 33, 47, and 61. On day 12, cows treated with GnRH were allocated to ipsilateral (n = 239) or contralateral (n = 241) groups based on the side of accessory CL formation relative to previous ovulation. Accessory CL cows had greater P4 than controls. In total, 52.7% (78/148) of pregnant cows in contralateral group had accessory CL regression earlier (<day 33; 30.8%) or later (days 33–61; 69.2%) in pregnancy with coincident decrease in P4. No cows with ipsilateral accessory CL underwent regression. There was no difference in pregnancy/AI among groups. Cows with contralateral accessory CL that underwent early regression had greater pregnancy loss (30%) than controls (10%), or cows with ipsilateral CL (3%) or contralateral CL with either later or no regression (12%). Cows with ipsilateral accessory CL had lower pregnancy loss than controls. In conclusion, elevating circulating P4 by the induction of accessory CL, particularly ipsilateral CL, increases P4 and reduces pregnancy loss. However, contralateral accessory CL that undergoes regression before day 33 of pregnancy has increased pregnancy loss, possibly due to an abrupt decrease in P4 at a pivotal period of pregnancy (days 26–33).