Luteal changes after treatment with sub-luteolytic doses of prostaglandin (cloprostenol sodium) in cattle

The effect of a double dose of cloprostenol sodium on luteal blood flow and pregnancy rates per artificial insemination in lactating dairy cows

Inadequate luteolysis in fertility programs is a problem for lactating dairy cows treated with a single dose of PGF_2α. The proportion of cows with complete luteolysis can be increased by administering 2 doses of PGF_2α 24 h apart. This study hypothesized that a double dose of cloprostenol sodium (1.0 mg) could take the place of 2 doses 24 h apart due to its enhanced half-life. Cows were allocated to receive 1 of 3 treatments: negative controls: 0.5 mg of cloprostenol sodium (single; n = 337); positive controls: two 0.5-mg doses of cloprostenol sodium 24 h apart (two/24; n = 313); and treated: 1.0 mg of cloprostenol sodium (double; n = 298) at the final PGF_2α of Double-Ovsynch. Cows received artificial insemination (AI) 16 h after final GnRH of Double-Ovsynch. Pregnancy diagnosis was determined at 24, 34, 62, and 184 d post-AI. Pregnancy loss was categorized in the following periods: between 24 to 34, 34 to 62, and 62 to 184 d post-AI. Ultrasonography (B-mode and color Doppler) was used to assess luteal function pre- and posttreatment with various doses of cloprostenol sodium. Luteal volume and luteal blood flow (LBF) from d 7 and 14 corpora lutea were determined before treatment (d -1), and 2 and 4 d after treatment. No evidence was observed of an effect of treatment on pregnancy rates per AI at 24, 34, or 62 d post-AI. No effect was observed of treatment on pregnancy losses occurring between d 24 and 34, 34, and 62, and between 62 and 184 d post-AI. However, third-plus parity cows treated with the single treatment had greater pregnancy loss compared with two/24 and double between d 24 and 34 post-AI. Third-plus parity cows that received the double treatment had lower LBF 2 and 4 d after treatment compared with cows treated with single. Amount of LBF present 4 d after treatment was not a predictor of pregnancy or pregnancy loss. A double dose (1.0 mg) of cloprostenol sodium may be a feasible alternative for fertility programs based on nondifferent outcomes to the two/24 treatment, lower pregnancy losses, and reduced LBF disappearance following treatment in third-plus parity cows in comparison with the single treatment.

Effect of cloprostenol sodium dose on luteal blood flow and volume measurements in Holstein heifers with both day-4 and day-10 corpora lutea

Establishment of a vascular system within the corpus luteum (CL) is critical for progesterone (P₄) secretion. Measurement of luteal blood flow (LBF) may be a feasible way to determine luteolysis induced with cloprostenol sodium (CLO). Our overall objective was to establish timelines to assess luteolysis via Doppler ultrasonography. Estrous cycles were synchronized in 11- to 12-mo-old Holstein heifers (n = 37). Heifers were injected CLO at a random stage of the estrous cycle 12 d from treatment. Gonadotropin-releasing hormone (GnRH) was administered 2 (d -10) and 8 d (d -4) after the initial CLO. This satisfied the study objective of inducing simultaneous presence of CL at d 4 of development (D4 CL) and CL at d 10 of development (D10 CL) on the day of treatment with different CLO doses (hereafter referred to as d 0). Heifers were randomly assigned to 1 of 5 treatments on d 0: negative control (NC) consisting of no treatment with CLO (n = 8); a quarter dose of CLO (0.125 mg; n = 8); half dose of CLO (0.25 mg; n = 8); full dose of CLO (0.5 mg; n = 8); or positive control (PC) consisting of 4 doses of 0.5 mg of CLO at 24-h intervals starting at d 0 (n = 5). Data collection was performed at d 0 (before and 1 h after treatment) and 2, 4, 6, and 8 d following treatment, to determine luteal volume (LV), LBF, and circulating concentrations of P₄. Both NC and PC were efficient in mimicking physiological scenarios that occur during normal luteal development and luteolysis. Heifers that received PC had complete LBF disappearance of both D4 and D10 CL between d 2 and 4 after the first of 4 CLO treatments given 24 h apart (average 4.0 ± 0.0 and 3.2 ± 0.7 d, respectively). Complete LBF disappearance was used as a luteolysis marker. Treatment with different doses of CLO did not impair luteal development of the D4 CL. However, concurrent complete LBF disappearance for D10 CL in heifers treated with half (5/8 heifers) and full doses of CLO (8/8 heifers) resulted in less LBF in the half dose, and less LV and LBF in the full-dose treatment, in D4 CL at d 8 post-treatment, compared with NC. Treatment with various doses of CLO induced an acute increase in LBF 1 h after treatment, regardless of dose in D10 but not in D4 CL. We found a lack of dose response in LV reduction of D4 and D10 CL. Interestingly, LV of the D10 CL decreased in untreated NC between d 0 and 8 after treatment (d 10-18 of luteal development). Assessment with color Doppler ultrasound was sensitive enough to identify dose-response patterns in Holstein heifers (absence, partial, or complete luteolysis) following various doses of CLO. Variability in time to complete LBF disappearance of mature D10 CL following a full dose of CLO limits the use of Doppler ultrasonography to detect luteolysis at a single time point following treatment.

Diestrous Ovulations in Pregnant Mares as a Response to Low Early Postovulatory Progestogen Concentration

Simple Summary

During early pregnancy in mares, progestogen is synthesized by the primary corpus luteum, which is the only source of progestogen until endometrial cup and accessory corpus luteum formation, from day 36 of pregnancy onwards. In the present study, we investigated the hormonal profile (gonadotrophin and progestogen concentrations) of 11 mares after experimental reduction of primary corpus luteum function. Two pregnancies of each mare were assigned to the control and treatment groups, respectively, and were analyzed until day 34. Low plasma progestogen concentration caused by the treatment reduced the negative feedback on the hypothalamic-pituitary axis, stimulating gonadotropin release, and luteal tissue response. Progestogen concentration restoration soon after treatment suggests a rebound effect and the resurgence of luteal function. In addition, diestrous ovulation was observed between days 11 and 15 in five treatment pregnancies (5/11), but none of the controls (0/11). Although the total luteal area increased after diestrous ovulations, corpus luteum size was not correlated to progestogen secretion. Results suggest that diestrous ovulations during early pregnancy in mares may reflect low progestogen concentrations in the early postovulatory period.

Abstract

Spontaneous prolongation of the luteal phase has been described in horses, but the underlying causes are still unclear. The present study investigated details of gonadotrophin and progestogen secretion in pregnant mares (n = 11) with or without experimentally reduced early postovulatory luteal function. From days 0 to 3 after ovulation, they were treated with the prostaglandin F_2α (PGF_2α) analogue cloprostenol or left untreated. After conceptus collection on day 34, they were assigned to the opposite treatment. Mares were affiliated to the group primary corpus luteum (n = 6) or diestrous corpus luteum (n = 5) depending on diestrous corpus luteum (CL) detection in the PGF pregnancy. For statistical comparisons, a p-value < 0.05 was significant. There was an effect of treatment (p < 0.01), but not of group on progestogen concentration. The concentration of LH was higher in PGF-treated than in untreated pregnancies (p < 0.05), but did not differ between groups. The FSH concentration did not differ between groups nor treatments. The total luteal tissue area was greater in mares with a diestrous ovulation during the PGF treatment pregnancy. Low progestogen concentration in the early postovulatory phase diminish the negative feedback on the hypothalamic-pituitary axis in early pregnancy and, thus, stimulate a luteal tissue response. Detection of secondary CL at the time of pregnancy examination in mares may reflect that early post-ovulatory progestogen concentrations were low.

Partial luteolysis during early diestrus in cattle downregulates VEGFA expression and reduces large luteal cell and corpus luteum sizes and plasma progesterone concentration

Our objectives were to investigate potential changes in the size of steroidogenic large luteal cells (LLC) during partial luteolysis induced by a sub-dose of cloprostenol in early diestrus and to determine transcriptional variations in genes involved in corpus luteum (CL) functions. Cows were subjected to an Ovsynch protocol, with the time of the second GnRH treatment defined as Day 0 (D0). On D6, cows were randomly allocated into three treatments: Control (2 mL saline, im; n = 10), 2XPGF (two doses of 500 μg of cloprostenol, im, 2 h apart; n = 8) or 1/6PGF (single dose of 83.3 μg of cloprostenol, im; n = 10). Before treatments and every 8 h during the 48-h experimental period, blood samples were collected and CL volumes measured. Furthermore, two CL biopsies were obtained at 24 and 40 h post-treatment. The 1/6PGF treatment caused partial luteolysis, characterized by sudden decreases in plasma progesterone (P₄) concentrations, luteal volume and LLC size, followed by increases (to pretreatment values) in P₄ and luteal volume at 24 and 40 h post-treatment, respectively. However, at the end of the study, P4, luteal volume and LLC size were all significantly smaller than in Control cows. Temporally associated with these phenotypes, there was a lower mRNA abundance of VEGFA at 24 and 40 h, and ABCA1 at 24 h (P < 0.05). In conclusion, a sudden reduction in CL size during partial luteolysis induced by a sub-dose of PGF_2α analog on day 6 of the estrous cycle was attributed to a reduction in LLC size, although these changes did not account for the entire phenomenon. In addition to its involvement in reducing CL size, decreased VEGFA mRNA abundance impaired CL development, resulting in a smaller luteal gland and lower plasma P₄ concentrations compared to Control cows.

Responses to intra-luteal administration of cloprostenol in dairy cows

The aim of the study was to determine the luteolytic dose of cloprostenol administered directly into the corpus luteum (CL; intra-luteal treatment, ILT) in dairy cattle. Cows of two control groups were treated with 500 μg of cloprostenol (Estrumate®) intramuscularly (IM-500) or via ILT with 0.2 mL of physiological solution (ILT-0). Cows of four experimental groups were treated by ILT with cloprostenol in doses 5, 25, 50 and 100 μg (ILT-5, -25, -50 and -100 groups). Progesterone concentrations (P4) and size of CL were evaluated to assess luteolysis at 0, 0.5, 1, 2, 4, 8, 24 and 48 h or at 0, 24 and 48 h after ILT, respectively. Cows in the ILT-0 and -5 groups were unaffected by ILT. The P4 concentrations were less in cows of the IM-500, as well as ILT-25, -50 and -100 groups at 48 h subsequent to ILT. The size of the CL was less in cows of IM-500, as well as ILT-25, -50 and -100 groups at 48 h after ILT. There were P4 concentrations of about 1 ng/mL 48 h after ILT in cows of the IM-500, as well as ILT-50 and -100 groups. In conclusion, the cloprostenol dose of 50 μg administered intra-luteally is a luteolytic dose in cows.

Short communication: Heat stress does not affect induced luteolysis in Holstein cows

Heat stress (HS) has deleterious effects on bovine reproduction, including prolongation of the luteal phase in Holstein cows, perhaps due to compromised luteolysis. The objective was to characterize effects of HS on luteolytic responses of nonlactating Holstein cows given 25 or 12.5 mg of PGF_2α on d 7 of the estrous cycle. Cows were randomly distributed into 2 environments: thermoneutral (n = 12; 25°C) or HS (n = 12; 36°C). In each environment, cows were treated with 2 mL of saline, 25 or 12.5 mg of PGF_2α (n = 4 cows per group). The HS environment induced a significant increase in rectal temperature and respiratory rate compared with the thermoneutral environment. Heat stress did not have significant effects on luteolytic responses or circulating progesterone concentrations. Rapid and complete luteolysis occurred in all cows given 25 mg of PGF_2α and in 4 of 8 cows given 12.5 mg; the other 4 cows given 12.5 mg had partial luteolysis, with circulating progesterone concentrations initially suppressed, but subsequently rebounding. Therefore, we conclude that HS does not change corpus luteum sensitivity to PGF_2α.

Progesterone-based timed AI protocols for Bos indicus cattle II: Reproductive outcomes of either EB or GnRH-type protocol, using or not GnRH at AI

The aim of these experiments was to study ovarian dynamics and fertility of Bos indicus beef cattle submitted to 7-d progesterone (P4)-based fixed-time AI (FTAI) protocols using different hormonal treatments. In Exp. 1, 2 yr old Nelore heifers (n = 973) were randomly assigned to one of four treatments: EB-0 (estradiol benzoate, EB on D0 and no GnRH at AI), EB-G (EB on D0 and GnRH at AI), G-0 (GnRH on D0 and no GnRH at AI), or G-G (GnRH on D0 and at AI). On D0, heifers received an intravaginal P4 implant (0.5 g) for 7 d and EB (1.5 mg) or GnRH (16.8 μg). On D7, the P4 implant was withdrawn and heifers received cloprostenol (PGF; 0.5 mg) and estradiol cypionate (EC, 0.5 mg). Heifers in G groups also received PGF and eCG (200 IU) on D6, whereas EB heifers received eCG on D7. At FTAI on D9, only EB-G and G-G groups received GnRH (8.4 μg). In Exp. 2, Nelore cows (n = 804) received the same treatments (EB-0, EB-G, G-0, or G-G) using a 1.0 g P4 implant, 2.0 mg EB, and 300 IU eCG. Effects were considered significant when P ≤ 0.05. After treatment on D0, G had more ovulations than EB in heifers (60.3 [287/476] vs. 12.7% [63/497]) and cows (73.7 [83/112] vs. 24.4% [28/113]). Luteolysis after D0 was greater in EB than G in heifers (39.2 [159/406] vs. 20.0% [77/385]) and cows (25.5 [14/55] vs. 1.6% [1/64]). Heifers in G had larger follicles (mm) than EB on D7 (10.3 ± 0.2 vs. 9.2 ± 0.2) and at AI (11.9 ± 0.2 vs. 11.3 ± 0.2). Cows had larger follicles in G than EB on D7 (11.0 ± 0.3 vs. 9.9 ± 0.3) but not at AI. More estrus was observed in G than EB for heifers (80.3 [382/476] vs. 69.6% [346/497]) and cows (67.6 [270/400] vs. 56.2% [227/404]). There was no interaction between D0 and D9 treatments on pregnancy per AI (P/AI) in heifers (EB-0: 56.7 [139/245], EB-G: 53.6 [135/252], G-0: 52.6 [127/241], and G-G: 57.5% [135/235]). However, cows from EB-G had greater P/AI than EB-0 (69.5 [142/204] vs. 60.2% [120/200]), whereas P/AI for G-0 (62.7% [127/203]) was similar to G-G (60.9% [120/197]). In heifers, there was no interaction of GnRH at AI with estrus, however, cows that did not display estrus had greater P/AI if they received GnRH at AI (GnRH = 59.1 [91/154] vs. No GnRH = 48.2% [78/162]). Thus, protocols initiated with EB or GnRH for Bos indicus heifers and cows had differing ovarian dynamics but similar overall fertility, enabling their use in reproductive management programs. Treatment with GnRH at time of AI increased fertility in some instances in Bos indicus cows but not in heifers.

Corpus luteum dynamics after ovulation induction with or without previous exposure to progesterone in prepubertal Nellore heifers

The objectives of this study were 1) to monitor corpus luteum (CL) dynamics after two different protocols of ovulation induction in prepubertal Nellore heifers, and 2) to determine differences in luteal function. Fifty-seven heifers (weight 289.61 ± 32.28 kg, BCS 5.66 ± 0.65, age 17.47 ± 0.81 months) were divided into two groups: GP4+GnRH received a progesterone (P4) device of 3rd use for 10 days, followed by the administration of 0.02 mg buserelin acetate (GnRH) 48 h after removal of the device, and GGnRH received only GnRH. The CLs formed were monitored by ultrasonography every 2 days until their functional regression (decrease in the color Doppler signal and serum P4 concentration < 1 ng/mL), determining their diameter and area, numerical pixel value (NPV), pixel heterogeneity, and vascularization percentage. The peak systolic velocity, end diastolic velocity, resistivity index and pulsatility index (PI) of the ovarian artery and serum P4 concentration were also measured. A lifespan of the CL of more than 16 days was classified as normal-function and of less than 16 days as premature regression. The variables were compared between treatments, CL categories (normal-functional, prematurely regressed or non-functional), days of evaluation, and their interactions using the MIXED procedure of the SAS program (p ≤ 0.05). Three animals of each group (6/57 = 11%) did not respond to treatment, corresponding to an ovulation rate of 89%. There was a higher percentage of normal-function CLs in GP4+GnRH (81%) and a higher percentage of non-functional CLs in GGnRH (52%; P4 concentration < 1 ng/mL in all assessments). Normal-function CLs exhibited a greater area, vascularization percentage and P4 concentration than prematurely regressed and non-functional CLs. Lower diameter, area, NPV and P4 concentration were observed for non-functional CLs, but there was no difference in vascularization percentage compared to prematurely regressed CLs. Progesterone concentration was efficient in diagnosing CL function and was positively correlated with CL area (r = 0.62; p < 0.001) and vascularization percentage (r = 0.38; p < 0.001). Diameter and PI were important for the early diagnosis of non-functional and prematurely regressed CLs, respectively. In conclusion, luteal function differed for the first CL that develops after ovulation induction in prepubertal heifers. Ultrasonographic parameters (diameter, area, NPV, vascularization percentage, and PI) can be used to predict CL function.

Hemodynamics of the corpus luteum in mares during experimentally impaired luteogenesis and partial luteolysis

The aim of the current project was to characterize the luteal vascularity and the plasma concentrations of progesterone (P4), prolactin (PRL) and 13,14-dihydro-15-keto-PGF_2α (PGFM) in mares with luteal disturbances during early and mid-diestrus. In Experiment 1, twenty-one mares were treated with 2 mL of 0.9% NaCl, or 1 mg Dinoprost, or 10 mg Dinoprost on day two after ovulation (Control-D2, 1/10PGF-D2 and PGF-D2 groups, respectively; n = 7 mares/group). In Experiment 2, similar treatments were performed eight days post-ovulation using a different cohort of 21 mares (Control-D8, 1/10PGF-D8 and PGF-D8 groups, respectively; n = 7 mares/group). Blood samples were collected hourly and power-Doppler examinations of the corpus luteum (CL) were performed every 6 h from H0 (moment immediately before treatment) to H48. Data collection was also done once a day from D0 (day of ovulation) to D20. In Experiment 1, the PGF-D2 and 1/10PGF-D2 groups had lower increase of plasma concentration of P4 until H48 and reduced maximum P4 concentrations on D8-D11 than mares from the Control-D2 group. However, no differences among groups were detected for luteal vascularity during early and mid-diestrus. In Experiment 2, complete and partial luteolysis were detected in mares from the PGF-D8 and 1/10PGF-D8 groups, respectively. Luteal vascularity and plasma P4 concentrations differed among Control-D8, PGF-D8 and 1/10PGF-D8 groups on H48. Partially regressed CLs (1/10PGF-D8 group) generated more Doppler signals than completed regressed CLs (PGF-D8 group) between D10 and D13. In both experiments, a transient increase in PRL activity was observed in parallel to the PGFM pulse in mares receiving 1 or 10 mg Dinoprost. The use of prostaglandin on D2 at conventional or 1/10 of the dose impaired the luteal development in mares. Moreover, the low dose of prostaglandin lead to partial regression of mature CLs. The blood supply was reduced in partially regressed CLs, but not in CLs undergoing impaired luteogenesis.

Luteolytic efficiency of reduced doses of cloprostenol in the ewe. Effect of progesterone concentrations at the time of treatment

Seventy six ewes were treated with 7.5, 12.5, 25 or 50μg of cloprostenol on day 6 or 9 post-estrus to compare the luteolytic efficiency of the PGF2α analogue at each stage and to evaluate if progesterone concentrations at the time of treatment affect such efficiency. Blood samples were obtained before cloprostenol administration and 12, 24, 48, and 72h thereafter. There was an effect of dose (p<0.05) but not of day post-estrus on the proportion of animals completing luteolysis. As the dose increased, the proportion of ewes completing luteolysis also increased. Also, as the dose increased from 7.5 to 25μg, more ewes showed a transient progesterone decline instead of an absence of response, indicating that in some ewes reduced doses initiated luteolysis but were not able to finish the process. Since the dose of 25μg resulted in close to 50% luteolytic efficacy, this group was used to study the effects of progesterone concentrations at the time of treatment on the response to cloprostenol. Pre-treatment progesterone concentrations were higher (p<0.01) in ewes experiencing luteolytic failure than in those that completed luteolysis. There was a negative correlation between initial progesterone concentrations and their reduction by 12h post-treatment. It is concluded that high progesterone concentrations are associated with a reduction in sensitivity to small doses of cloprostenol. Possible mechanisms and implications of this luteoprotective effect are discussed.

A weekly postpartum PGF2α protocol enhances uterine health in dairy cows

Postpartum uterine health in dairy cows is crucial for the maintenance of good reproductive performance. In order to improve uterine health and reduce puerperal intrauterine infection, 608 Holstein cows received a weekly PGF_2α protocol (3 i.m. injections of PGF_2α at 7, 14 and 21 d postpartum). For comparison, 593 cows in the control group received injections of sterile saline at the same time. Uterine score at 14 d postpartum, the prevalence of endometritis at 21-27 d postpartum, and subsequent reproduction performance was evaluated. Cows in the treated group exhibited higher tonicity (P<0.05) of the uterus, with less prevalence of endometritis (10.4%, 63/608 vs. 34.6%, 205/593; P<0.001), and required shorter time to the first AI postpartum (67.5±3.4 d vs. 84.4±3.7 d, P<0.05) and to pregnancy (114.5±5.4 d vs. 131.4±5.8 d, P<0.05). In conclusion, the present study demonstrated that uterine health in Holstein cows can be promoted while puerperal infection can be suppressed by this weekly postpartum PGF_2α protocol.