Diurnal variation in LH and temporal relationships between oscillations in LH and progesterone during the luteal phase in heifers

Diurnal rhythms in testicular blood flow, testicular morphometry and reproductive hormones in Shiba goats

Context Testicular blood flow (TBF) is crucial for testicular function. The pattern of TBF in Shiba goats indicates seasonal variations. Aims This study aimed to investigate the effect of diurnal variations on TBF, testis volume (TV), testicular echogenicity, and reproductive hormones in goats over a 24-h period. Methods In three trials that went for three consecutive days each, 12 bucks were scanned using Triplex ultrasonography to assess the TV, pixel intensity of testicular echotexture (PIX), and Doppler indices of TBF (resistive index: RI and pulsatility index: PI) in four-time points a day (at 6.00, 12.00, 18.00, and 00.00 h). Concomitantly, the changes in circulating FSH, LH, inhibin, testosterone (T), estradiol (E2), cortisol, and melatonin were assessed. Key results Results revealed diurnal alterations in the calculated RI of TBF and the PIX of testicular parenchyma (P < 0.05). Lower RI values of the TBF were observed at 6.00 h compared to other time points. There were significant diurnal alterations in the levels of FSH (P < 0.05), LH (P < 0.05), T (P < 0.0001), E2 (P < 0.0001), cortisol (P < 0.0001), and melatonin (P < 0.0001). FSH attained a higher concentration at 18.00 h compared to 12.00 h. Concentrations of LH were significantly higher at 06.00 h compared to those at 18.00 h. Concentrations of T were significantly higher at 6.00 compared to other time points. E2 showed higher concentrations at 6.00 h and 00.00 h compared to 12.00 h and 18.00 h. On the contrary, concentrations of cortisol were significantly higher at 12.00 h and 18.00 h compared to 06.00 h and 00.00 h. The highest concentrations of melatonin were observed at 00.00 h compared to other time points, while the lowest concentrations were at 12.00 h. Conclusions Diurnal rhythm induces significant changes in TBF, testicular PIX, and circulating FSH, LH, T, E2, cortisol, and melatonin over the 24-h day. Implications The outcomes of the study are reflected in the advisability of monitoring the TBF at a fixed time a day to avoid the circadian rhythm effect.

Effect of circadian system disruption on the concentration and daily oscillations of cortisol, progesterone, melatonin, serotonin, growth hormone, and core body temperature in periparturient dairy cattle

Metabolic, circadian, sleep, and reproductive systems are integrated and reciprocally regulated, but the understanding of the mechanism is limited. To study this integrated regulation, the circadian timing system was disrupted by exposing late pregnant nonlactating (dry) cows to chronic shifts in the light-dark phase, and rhythms of body temperature and circulating cortisol (CORT), progesterone (P4), serotonin (5HT), melatonin (MEL), and growth hormone (GH) concentrations were measured. Specifically, across 2 identical studies (1 and 2), at 35 d before expected calving (BEC) multiparous cows were assigned to control (CON; n = 24) and exposed to 16 h light and 8 h dark or phase shift (PS; n = 24) treatments and exposed to 6-h light-dark phase shifts every 3 d until parturition. All cows were exposed to control lighting after calving. Blood samples were collected in the first study at 0600 h on d 35 BEC, d 21 BEC, and 2 d before calving, and d 0, 2, 9, 15, and 22 postpartum (PP). A subset of cows (n = 6/group) in study 1 was blood sampled every 4 h over 48 h beginning on d 23 BEC, 9 BEC, and 5 PP. Body temperature was measured every 30 min (n = 8-16/treatment) for 48 h at 23 BEC and 9 BEC in both studies; and at 14 PP and 60 PP only in study 2. Treatment did not affect levels of CORT, GH, or P4 at 0600 h, but overall level of 5HT was lower and MEL higher in PS cows across days sampled. A 2-component versus single-component cosinor model better described [>coefficient of determination (R²); <Akaike information criterion and <Bayesian information criterion] daily oscillations of all hormones and temperature for both treatments. Circadian rhythm fit (R²) of body temperature and MEL increased from 23 BEC to 9 BEC in CON and was marked by loss of feeding time influence on oscillations in both treatments. Both treatments exhibited circadian rhythms of CORT at 9 BEC, CON cows also exhibited circadian rhythms in P4 at 23 BEC, and 5HT at 9 BEC. Daily oscillations in temperature and hormones, except CORT, were affected by PS treatment in the prepartum and were associated with longer gestation. In the PP, circadian rhythmicity was lost or diminished for all hormones and body temperature in both treatments. Stronger rhythms of body temperature and multiple hormones at 1 wk prepartum may indicate a synchronizing cue to time parturition. Therefore, dairy systems may need to consider management factors that affect circadian clocks in late-gestation cows.

Prostaglandin F2α influences pre-ovulatory follicle characteristics and pregnancy per AI in anovular dairy cows

Objectives were to determine the effects of a dose of PGF_2α administered 2 days before timed artificial insemination (AI) on LH pulsatility, characteristics of the pre-ovulatory follicle, and pregnancy per artificial insemination (P/AI) in anovular dairy cows, particularly in cows not subjected to hyperthermia. In experiment 1, 2,011 lactating Holstein cows had ovaries scanned by ultrasound to determine corpus luteum (CL) presence and only those without a CL in two consecutive exams were enrolled (n = 437). Cows had the estrous cycle synchronized with an estradiol-progesterone based protocol starting on experiment Day -11 and timed AI on Day 0. Cows were assigned randomly to receive a single dose of 25 mg of PGF_2α as dinoprost on Day -4 (1PGF, n = 222) or two doses of 25 mg each of PGF_2α, one on Day -4 and one on Day -2 (2PGF, n = 215). Rectal temperatures were evaluated on the day of AI and 7 days later and cows were classified as being normothermic (<39.1 °C) or hyperthermic (≥39.1 °C). Ovulatory responses and P/AI were determined. In experiment 2, cows with regressed CL were exposed to low concentrations of progesterone and then randomly assigned to the same estrous synchronization protocol and treatments, 1PGF (n = 28) and 2PGF (n = 28). Blood was sampled and analyzed for concentrations of progesterone, and for concentrations of LH and 13,14-dihydro-15-keto-PGF_2α metabolite (PGFM) every 15 min starting 1 h before to 6 h after treatments and then every 2 h from 12 to 59 h after treatments. The pre-ovulatory follicle was aspirated 44 h after treatments and concentrations of estradiol quantified. In experiment 1, treatment of anovular cows with a second dose of PGF_2α increased P/AI in normothermic cows (19.8 [18/91] vs. 38.8% [31/80]), but not in hyperthermic cows. Synchronization was not affected by treatment, but it was greater for normothermic than hyperthermic cows (87.1 [149/171] vs. 77.8% [207/266]). When only synchronized cows were evaluated, the same responses were observed; treatment with 2PGF increased P/AI compared with 1PGF in normothermic cows (23.1 [18/78] vs. 43.7% [31/71]), but not in hyperthermic cows. In experiment 2, administration of 25 mg of dinoprost in 2PGF resulted in concentrations of PGFM 26-fold greater than 1PGF in the first 6 h after treatment (48 vs. 1,242 pg/mL). Cows receiving 2PGF had smaller basal LH concentration (0.57 vs. 0.46 ng/mL) and less frequent LH pulses (4.5 vs. 3.9 pulses/6 h), but duration of the LH surge was longer for 2PGF than 1PGF (13.1 vs. 15.5 h). Treatment with 2PGF increased the diameter and volume of the pre-ovulatory follicle, and concentration of estradiol (115 vs. 262 ng/mL) and total follicular estradiol content (124 vs. 505 ng) compared with 1PGF. Collectively, these results suggest that PGF_2α has a role in fertility of anovular cows that is unrelated to its luteolytic effect.

Physiologic responses to feeding rumen-protected glucose to lactating dairy cows

It was hypothesized that rumen-protected glucose (RPG) in diets of dairy cows increases concentrations of insulin resulting in greater blood progesterone concentrations because elevated insulin decreases activity of liver enzymes inactivating steroid hormones. Timing of ovulation was synchronized among 64 postpartum Holstein cows using GnRH and PGF_2α (Day 0 = ovulation). Cows were milked thrice daily and assigned randomly a basal diet supplemented with 0, 1, 2, or 4 kg of an RPG product in place of corn grain, top-dressed in the diet beginning on Day -3. Blood was collected pre- and post-prandial on Days 0, 2, and 4 to determine plasma glucose and insulin concentrations and daily from Days 2 through 12. Intake of crude protein and energy-soluble carbohydrates increased linearly with dose, whereas starch intake decreased linearly with dose. Neither daily milk yield nor dry matter intake (DMI), energy-corrected milk (ECM), somatic cell count, or percentages of milk fat, protein and lactose on Day 8 differed among dietary treatments. Neither pre- nor post-prandial changes in plasma glucose differed among treatments. In contrast, post-prandial glucose decreased from Days 0 through 4. A change in plasma insulin (post-prandial minus pre-prandial) was detected. Milk urea nitrogen increased linearly with RPG dose. Concentrations of progesterone were unaffected by RPG dose. It is concluded that insulin response to RPG was decreased relative to the control and RPG supplementation linearly increased crude protein intake and milk urea nitrogen with increasing dose, but did not affect concentrations of progesterone, milk yield, or dry matter intake.

Determination, intercorrelation and intraindividual stability of five steroids in hair, saliva and urine among chinese college students

Hair steroids and their ratios are believed to be reliable biomarkers reflecting the long-term exposure of circulating steroids. Hereinto, two underlying assumptions are that hair biomarkers have consistency with traditional biomarkers in saliva or urine, and good long-term intraindividual stability across a long time. However, these two assumptions have not been well verified for most of hair biomarkers except for hair cortisol. Thus, this study aimed to verify the two issues on eight hair biomarkers: cortisol, cortisone, dehydroepiandrosterone (DHEA), testosterone, progesterone, the ratios of cortisol to cortisone, DHEA and testosterone. The five steroids in hair, saliva and urine were measured with high performance chromatography tandem mass spectrometry. The results revealed that the hair biomarkers had significant correlations with the salivary biomarkers calculated by the mean area under curve (AUC_g) in a matched time span (ps < 0.05) where the coefficients of correlations (r) were >0.3 (r = 0.322-0.616) except cortisone and progesterone (r = 0.177 and 0.212, respectively). It indicated that hair biomarkers had weak to moderate consistency with salivary ones. But only three biomarkers showed the consistency between hair and urine, such as testosterone (r = 0.352, p < 0.01), progesterone (r = 0.228, p < 0.05) and the ratio of cortisol to testosterone (r = 0.502, p < 0.01). Hair biomarkers showed no absolute stability, but moderate to high long-term relative stability across 12 months where interclass correlation coefficients ranged between 0.356 and 0.678 (ps < 0.01). These results implied that the eight biomarkers in hair could retrospectively reflect their cumulative exposure in vivo. Therefore, the hair biomarkers would be considerable reliable long-term biomarkers for psychological and physiological research.

Trio a novel bovine high-fecundity allele: II. Hormonal profile and follicular dynamics underlying the high ovulation rate

The newly discovered Trio high-fecundity allele produces multiple ovulations in cattle. This study evaluated (1) size and growth rates of follicles in Trio carriers during a synchronized follicular wave, induced by follicle aspiration; (2) follicle-stimulating hormone (FSH) patterns associated with the follicular wave; (3) size of corpora lutea (CL) and circulating progesterone; and (4) intrafollicular estradiol concentrations prior to normal deviation. Trio carriers had mean dominant follicles that were significantly smaller in diameter and volume than noncarriers. Onset of diameter deviation occurred at ∼3 days after the last follicle aspiration in both genotypes despite Trio carriers having much smaller individual follicles. Follicles of Trio carriers grew at a slower rate than noncarrier follicles (∼65% in mm/day or ∼30% in mm3/day) resulting in much smaller individual dominant follicles (∼25% volume). However, total dominant follicle volume, calculated as the sum of all dominant follicles in each animal, was similar in carriers and noncarriers of Trio throughout the entire follicular wave. Circulating FSH was greater in Trio carriers during the 24 h encompassing deviation. Trio carriers had significantly more ovulations than noncarriers, and individual CL volume was smaller, although total luteal tissue volume and circulating P4 were not different. Thus, increased ovulation rate in Trio carriers relates to smaller individual follicles (one-third the volume) near the time of deviation due to slower follicle growth rate, although time of deviation is similar, with increased circulating FSH near deviation leading to selection of multiple dominant follicles in Trio carriers with similar total follicle volume.

Trio, a novel bovine high fecundity allele: III. Acquisition of dominance and ovulatory capacity at a smaller follicle size

The acquisition of dominance and ovulatory capacity was evaluated in follicles from cows that were carriers or half-sibling noncarriers of the Trio allele. Follicle size at acquisition of follicular dominance was determined by evaluating whether follicles ovulate after GnRH challenge (ovulatory capacity-experiment 1) and by determination of intrafollicular concentrations of estradiol and free insulin like growth factor 1 (IGF1) and relative mRNA expression of cytochrome P450 family 19 subfamily A member 1 (CYP19A1), luteinizing hormone/choriogonadotropin receptor (LHCGR), and pappalysin 1 (PAPPA, previously known as pregnancy-associated plasma protein A, pappalysin 1) in granulosa cells from follicles of different sizes (experiment 2). Ovulatory capacity developed in follicles at 8.3 mm (50% ovulatory capacity) in noncarriers but at smaller sizes (5.5 mm) in Trio carriers. Similarly, in experiment 2, follicles of Trio carriers acquired a dominant phenotype, as determined by intrafollicular estradiol and CYP19A1, LHCGR, and PAPPA mRNA expression in granulosa cells, at significantly smaller sizes but at a similar time after wave emergence. Overall, dominance/ovulatory capacity was acquired when follicles of Trio carriers were ∼30% the size (volume basis) of follicles in noncarriers. In addition, follicles in Trio carriers appear to acquire dominance in a hierarchal manner, as demonstrated by the progressively greater number of follicles with a dominant phenotype between days 2 and 4 after wave emergence. Thus, results from this study provide further support for a physiological model in which selection of multiple follicles in Trio allele carriers is characterized by acquisition of dominance at a smaller follicle size but at a similar time in the follicular wave with multiple follicles acquiring dominance in a hierarchal sequence.

Locational relationship between corpus luteum and ovulatory follicle on ovaries alters follicular dynamics and progesterone concentrations of Thai indigenous beef cows exhibiting two follicular waves

The present study aims to determine the impact of differences in the locational relationship between the previous corpus luteum (CL) and the further ovulatory follicle (OF) on follicular dynamics and progesterone (P4) concentrations in Thai indigenous beef cows (White Lamphun) exhibiting two follicular waves. Twenty-one cows, exhibiting the two-wave follicular pattern, were studied through interovulatory intervals (IOI), and classified according to the relationship between the previous CL and the further OF on the cattle model ovaries. Classifications were outlined as either an ipsilateral (same ovary) relationship (n = 12), or a contralateral (opposite ovaries) relationship (n = 9). Ultrasound monitoring, which evaluated the follicular diameter, and collection of blood for determining the P4 concentration were performed each day throughout the IOI. The IOI was longer (P &lt; 0.05) in the contralateral cows than in the ipsilateral cows (19.7 ± 0.33 days vs 18.5 ± 0.29 days). Cows with an ipsilateral relationship were found to have further OFs with greater (P &lt; 0.05) diameters than were cows with a contralateral relationship (13.9 ± 0.31 mm vs 12.1 ± 0.21 mm). The mean growth rate of the further OF was greater (P = 0.05) in the ipsilateral cows than in the contralateral cows (1.1 ± 0.11 mm/day vs 0.8 ± 0.04 mm/day). On Day 17 of the IOI, the ipsilateral cows demonstrated their lowest concentration of P4 (P &lt; 0.05). On Day 18 of the IOI, the concentrations of P4 tended to be lower (P = 0.09) in the ipsilateral cows than in the contralateral cows (0.6 ± 0.04 ng/mL vs 1.1 ± 0.12 ng/mL). The interval from the luteinisation until the end of the luteolysis was longer (P &lt; 0.05) in the contralateral group than in the ipsilateral group (18.5 ± 0.50 days vs 16.7 ± 0.33 days). Thus, we conclude that in Thai indigenous beef cows, the growth rate and diameter of the further OF during luteolysis increases more in the ipsilateral relationship than in the contralateral relationship.

Ultrasonography-accessed luteal size endpoint that most closely associates with circulating progesterone during the estrous cycle and early pregnancy in beef cows

The aim was to evaluate the associations between circulating P4 concentrations, corpus luteum (CL) size (diameter, area or volume) and blood perfusion (BP) in cows. In Experiment 1, Pearson's correlations (P < 0.05) with P4 concentrations were observed during CL development (D8) for total area (TA; r = 0.76), luteal area (ACL; r = 0.72), total and luteal diameter (TD and DCL respectively; r = 0.46). During mid-late diestrus, there was a positive correlation (P < 0.05) only at D15 with TA and ACL (r > 0.60), TD, total volume (TV) and luteal volume (VCL; r > 0.434). During luteal regression, the correlation was only observed at D18 for ACL (r = 0.478) and D20 with several variables. In Experiment 2, CL weight and ACL had the greatest correlation with P4 (r > 0.6). In Experiment 3, TA and ACL were the variables that were most closely correlated with serum P4 concentrations at D7 in recipient cows. Correlation coefficients were greater for luteal measurements when there were compact compared with cavitary CLs. In Experiment 4, there was no correlation (P > 0.05) between P4 and any of the variables measured on D4 and D7 in recipient cows detected in estrus. On D18 to D20, all CL characteristics were correlated (P < 0.05) with plasma P4, and luteal BP and BP area were more closely (P < 0.05) correlated than ACL. In conclusion, CL perimeter area measurements had the greatest association with luteal function during CL development; whereas for BP there was a greater correlation with P4 than luteal size during luteolysis.

An intraovarian mechanism that enhances the effect of an FSH surge on recovery of subordinate follicles in heifers

The effect of the future dominant follicle (DF), corpus luteum (CL), and side (left ovary [LO] and right ovary [RO]) on FSH-induced recovery (increase in diameter) of regressing subordinate follicles was studied in heifers. The DF of wave 2 and the largest subordinate follicle remained intact (controls, n = 14 heifers) or were ablated (n = 14 heifers) on a mean of 13 d postovulation when the DF was ∼10 mm (hour 0). Concentration of FSH (P < 0.0004) and diameter of subordinate follicles (P < 0.0002) decreased between hours -48 to 0 combined for the control and ablation groups. Thereafter, follicle diameter continued to decrease in the controls. Concentration of FSH increased (P < 0.05) and diameter of subordinates began to increase at hour 12 in the ablation group. Follicle-stimulating hormone increased to hour 24 and then returned to the hour 0 concentration by hour 72, completing the induced FSH surge. Concentration of LH began to increase at hour 0 in each group and at a similar rate between groups. Follicle recovery in the ablation group was compared among 8 subgroups as defined by the 2 sides and 4 intraovarian patterns (DF-CL pattern, both structures in same ovary; DF pattern, DF alone; CL pattern, CL alone; and devoid pattern, both structures absent). Follicle diameter increased (P < 0.05) between hours 24 and 48, and diameter at hours 24, 48, 72, and 96 involved a 3-way interaction (P < 0.0001) of pattern, side, and hour. The interaction was similar when diameter of the DF that originated from a recovered subordinate was either included or excluded in the analysis. Diameter of subordinate follicles in the ablation group at hour 96 was greater (P < 0.05) in the DF-CL/RO and DF/RO subgroups than that in the devoid/LO, devoid/RO, and CL/LO subgroups. The DF-CL/LO and CL/RO subgroups were intermediate. For follicles that decreased in diameter before hour 0, a greater (P < 0.05) percentage increased after hour 0 when the ovary contained a DF and was in the RO (DF-CL/RO and DF/RO subgroups) than for the remaining subgroups even after excluding the DF that originated from a subordinate. Results supported the hypotheses that (1) an induced FSH surge can stimulate the recovery of regressing subordinate follicles and (2) recovery of regressing subordinate follicles by FSH involves an intraovarian mechanism. Our interpretation is that the intraovarian mechanism that enhances the stimulatory effect of FSH on recovery of subordinate follicles was effective only in RO and only when it contained a DF.

Characteristics and functions of a minor FSH surge near the end of an interovulatory interval in Bos taurus heifers

The apparent function of a minor FSH surge based on temporality with follicular events was studied in 10 heifers with 2 follicular waves per interovulatory interval. Individual follicles were tracked from their emergence at 2 mm until their outcome was known, and a blood sample was collected for FSH and LH assay every 12 h from day -14 (day 0 = ovulation) to day 4. A minor FSH surge occurred in each heifer (peak, day -4.6 ± 0.2). Concentration of LH increased (P < 0.05) during the FSH increase of the minor surge but did not decrease during the FSH decrease. A minor follicular wave with 8.2 ± 2.0 follicles occurred in 6 of 10 heifers. The maximal diameter (mean, 3.4 ± 0.9 mm) of 77% of the minor-wave follicles occurred in synchrony on day -4.4 ± 0.4. Most (59%) of minor-wave follicles regressed before ovulation and 41% decreased and then increased in diameter (recovered) on day -1.9 ± 0.3 to become part of the subsequent wave 1. A mean of 3.7 ± 0.9 regressing subordinate follicles from wave 2 recovered on the day before or at the peak of the minor FSH surge. The growth rate of the preovulatory follicle decreased (P < 0.02) for 3 d before the peak of the minor FSH surge and then increased (P < 0.03). Concentration of LH increased slightly but significantly temporally with the resurgence in growth rate of the preovulatory follicle. A minor LH surge peaked (P < 0.0002) on day 3 at the expected deviation in growth rates between the future dominant and subordinate follicles. Results indicated on a temporal basis that the recovery of some regressing subordinate follicles of wave 2 was attributable to the minor FSH surge. The hypothesis was supported that some regressing follicles from the minor follicular wave recover to become part of wave 1.

A novel monoclonal antibody-based enzyme-linked immunosorbent assay to determine luteinizing hormone in bovine plasma

The development of a novel enzyme-linked immunosorbent assay (ELISA) for determining luteinizing hormone (LH) in bovine plasma is described. Anti-bovine LH (bLH) monoclonal antibodies (mAbs) were produced and characterized. One mAb recognizing the bLH β subunit was used for immunoaffinity purification of substantial amounts of biologically active bLH from pituitary glands. The purified bLH in combination with 2 anti-bLH β subunit mAbs was used to develop a sandwich ELISA, which satisfied all the criteria required to investigate LH secretory patterns in the bovine species. The ELISA standard curve was linear over the range 0.05 to 2.5 ng/mL, and the assay proved suitable for measuring bLH in plasma without any prior treatment of samples. Cross-reactivity and recovery tests confirmed the specificity of the method. The intra- and inter-assay coefficients of variation ranged between 3.41% and 9.40%, and 9.29% and 15.84%, respectively. The analytical specificity of the method was validated in vivo by provocative tests for LH in heifers, using the LH releasing peptide gonadotropin-releasing hormone. In conclusion, the adoption of mAbs for this ELISA for coating the wells and labeling, combined with the easy one-step production of reference bLH, ensures long-term continuity in large-scale measurements of LH in the bovine species.

Corpus luteum development and function after supplementation of long-acting progesterone during the early luteal phase in beef cattle

Strategic supplementation of P4 may be used to increase conception rates in cattle, but timing of supplementation in relation to ovulation, mass of supplementary P4 and formulation of the P4-containing supplement has not been determined for beef cattle. Effects of supplementation of long-acting progesterone (P4) on Days 2 or 3 post-ovulation on development, function and regression of corpus luteum (CL) were studied in beef cattle. Cows were synchronized with an oestradiol/P4-based protocol and treated with 150 or 300 mg of long-acting P4 on Day 2 or 3 post-ovulation (6-7 cows/group). Colour-doppler ultrasound scanning and blood sample collection were performed from Day 2-21.5. Plasma P4 concentrations were greater (p < 0.05) from Day 2.5-5.5 in the Day 2-treated groups and from Day 3.5-5.5 in the Day 3-treated cows than in the control group. CL area and blood flow during Day 2-8.5 did not differ (p > 0.05) among groups, suggesting no effect of P4 treatment on luteal development. The frequency of cows that began luteolysis before Day 15 was greater (p < 0.04) in cows treated with 300 mg than in the controls, but there were no differences between non-treated and 150 mg-treated cows. The interval from pre-treatment ovulation to functional and structural luteolysis was shorter (p < 0.01) in the combined P4-treated groups than in the control cows. In conclusion, was showed for the first time that long-acting P4 supplementation on Day 2 or 3 post-ovulation increases P4 concentrations for ≥3 day, has no effect on luteal development, but anticipates the beginning of luteolysis in beef cattle.

Endocrinology of number of follicular waves per estrous cycle and contralateral or ipsilateral relationship between corpus luteum and preovulatory follicle in heifers

A 3-d extension of the luteal phase occurs in interovulatory intervals (IOIs) with a contralateral relationship between the corpus luteum (CL) and preovulatory follicle with 3 follicular waves (Contra-3W group). Concentrations of FSH, progesterone, LH, and estradiol-17β for the ipsilateral versus contralateral CL and/or follicle relationship and 2 versus 3 waves per IOI were studied in 14 heifers. Follicular waves and FSH surges were designated 1, 2, or 3, according to order of occurrence in the IOI. The day (day 0 = ovulation) of the FSH peak in surge 2 occurred earlier (P < 0.02) in 3-wave IOIs (day 6.3 ± 0.5) than in 2-wave IOIs (day 8.5 ± 0.5). Mean FSH was higher in 3-wave than in 2-wave IOI on 82% of the days in the IOI. Repeatability or individuality in FSH concentration was indicated by a correlation (r = 0.54, P < 0.04) in FSH concentrations between ovulations at the beginning and at the end of the IOI. Concentrations of LH and estradiol increased (P < 0.05) near the beginning of the luteolytic period in 2-wave IOI regardless of the CL and/or follicle relationship. In the Contra-3W group, LH and estradiol remained at basal concentrations concurrently with FSH surge 3 and extension of the luteal phase. The hypotheses were supported that FSH surge 2 occurs earlier in 3-wave IOIs than in 2-wave IOIs and that the development of 3-wave IOIs occurs in individuals with greater FSH concentrations. Extension of the luteal phase in the Contra-3W group was temporally associated with lower concentrations of LH and estradiol.

Follicular-phase concentrations of progesterone, estradiol-17β, LH, FSH, and a PGF2α metabolite and daily clustering of prolactin pulses, based on hourly blood sampling and hourly detection of ovulation in heifers

Circulating concentrations of hormones were determined each hour in 13 heifers from the end of the luteolytic period to ovulation (follicular phase, 3.5 days). Diameter of the preovulatory follicle was determined every 8 hours, and the time of ovulation was determined hourly. The diameter of the preovulatory follicle decreased 0.8 ± 0.1 mm/h in heifers when there was 1 to 3 hours between the last two diameter measurements before ovulation. The concentration of progesterone (P4) after the end of the luteolytic period (P4 < 1 ng/mL) changed (P < 0.0001), as shown by a continued decrease until Hour -57 (Hour 0 = ovulation), then was maintained at approximately 0.2 ng/mL until 2 hours before the peak of the LH surge at Hour -26, and then a decrease to 0.1 ng/mL along with a decrease in estradiol-17β. Concentrations of LH gradually increased (P < 0.007) and concentrations of FSH gradually decreased (P < 0.0001) after the end of luteolysis until the beginning nadirs of the respective preovulatory surges. A cluster of prolactin (PRL) pulses occurred (P < 0.0001) each day with approximately 24 hours between the maximum value of successive clusters. Hourly concentrations of a PGF2α metabolite decreased (P < 0.007) until Hour -40, but did not differ among hours thereafter. Novel observations included the gradual increase in LH and decrease in FSH until the beginning of the preovulatory surges and follicle diameter decrease a few hours before ovulation. Results supported the following hypotheses: (1) change in the low circulating P4 concentrations during the follicular phase are temporally associated with change in LH concentrations; and (2) PRL pulses occur in a cluster each day during the follicular phase of the estrous cycle.

Circadian influence on the preovulatory LH surge, ovulation, and prolactin concentrations in heifers

A novel circadian study of the effect of clock hours on the preovulatory LH surge, ovulation, and maximal PRL concentration was done in 13 nontreated Holstein heifers. Hourly blood sampling and hourly ultrasound examinations to detect the hour of ovulation began at 8 and 48 hours, respectively, after CL area (cm(2)) had decreased 15% from the area at 15 days postovulation. The resulting experimental period began at the beginning of postluteolysis (progesterone, <1 ng/mL) and encompassed a mean of 3.5 days until ovulation. The frequency of the peak of the preovulatory LH surge for the three 8-hour periods of a 24-hour day was different (P < 0.02) between 2:00 AM to 9:00 AM (N = 9), 10:00 AM to 5:00 PM (N = 3), and 6:00 PM to 1:00 AM (N = 1). The median was 6:00 AM. The frequency of ovulations for 8-hour periods was different (P < 0.02) between 3:00 AM to 10:00 AM (N = 9), 11:00 AM to 6:00 PM (N = 3), and 7:00 PM to 2:00 AM (N = 1). The median was 7:30 AM. Two or three clusters of PRL pulses occurred during the 3.5 days. Based on all available PRL pulse clusters (N = 36), the clock hours of the maximal concentration/cluster was greater (P < 0.0001) for 9:00 AM to 2:00 PM (N = 33 clusters) than for each of the three other 6-hour periods (N = 0, 1, or 2 per period). The median was 11:30 AM. The hypothesis was supported that the peak of the preovulatory LH surge, ovulation, and maximal PRL concentration during pulse clusters occur with greater frequency during certain clock hours in heifers.

Effect of progesterone on magnitude of the luteinizing hormone surge induced by two different doses of gonadotropin-releasing hormone in lactating dairy cows

Ovulation to the first GnRH injection of Ovsynch-type protocols is lower in cows with high progesterone (P4) concentrations compared with cows with low P4 concentrations, suggesting that P4 may suppress the release of LH from the anterior pituitary after GnRH treatment. The objectives of this study were to determine the effect of 1) circulating P4 concentrations at the time of GnRH treatment on GnRH-induced LH secretion in lactating dairy cows and 2) increasing the dose of GnRH from 100 to 200 μg on LH secretion in a high- and low-P4 environment. A Double-Ovsynch (Pre-Ovsynch: GnRH, PGF(2α) 7d later, GnRH 3d later, and Breeding-Ovsynch 7d later: GnRH, PGF(2α) 7d later, and GnRH 48 h later) synchronization protocol was used to create the high- and low-P4 environments. At the first GnRH injection of Breeding-Ovsynch (high P4), all cows with a corpus luteum ≥ 20 mm were randomly assigned to receive 100 or 200 μg of GnRH. At the second GnRH injection of Breeding-Ovsynch (low P4) cows were again randomized to receive 100 or 200 μg of GnRH. Blood samples were collected every 15 min from -15 to 180 min after GnRH treatment, and then hourly until 6h after GnRH treatment. As expected, mean P4 concentrations were greater for cows in the high- than the low-P4 environment. For cows receiving 100 μg of GnRH, the LH peak and area under the curve (AUC) were greater in the low- than in the high-P4 environment. Similarly, for cows receiving 200 μg of GnRH, the LH peak and AUC were greater in the low- than the high-P4 environment. Cows receiving 100 or 200 μg of GnRH had greater mean LH concentration in the low- than the high-P4 environment from 1 to 6h after GnRH treatment. On the other hand, when comparing the effect of the 2 GnRH doses in the high- and low-P4 environments, cows receiving 200 μg of GnRH had a greater LH peak and AUC than cows treated with 100 μg of GnRH both in the high- and low-P4 environments. For the high-P4 environment, mean LH was greater from 1.5 to 5h after GnRH treatment for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH. In the low-P4 environment, mean LH was greater for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH from 1 to 2.5h after GnRH treatment. We conclude that the P4 environment at GnRH treatment dramatically affects GnRH-induced LH secretion, and that a 200-μg dose of GnRH can increase LH secretion in either a high- or a low-P4 environment.

Induction of PGFM pulses and luteolysis by sequential estradiol-17β treatments in heifers

The effects of sequential induction of PGFM pulses by estradiol-17β (E2) on prominence of PGFM pulses and progesterone (P4) concentration were studied in heifers. Three treatments of vehicle (n = 12) or E2 (n = 12) at doses of 0.05 or 0.1 mg were given at 12-h intervals beginning on Day 15 postovulation. Blood samples were collected every 12 h from Days 13-24 and hourly for 12 h after the first and third treatments. On Day 15, all heifers were in preluteolysis and on Day 16 were in preluteolysis in the vehicle-treated heifers (n = 11) and either preluteolysis (n = 4) or luteolysis (n = 8) in the E2-treated heifers. Peak concentration of induced PGFM pulses during preluteolysis on Day 15 was greater (P < 0.04) than for pulses during preluteolysis on Day 16. The interval from ovulation to the beginning of luteolysis was shorter (P < 0.04) in the E2-treated heifers than in the vehicle-treated heifers. An E2-induced PGFM pulse was less prominent (P < 0.008) in heifers in temporal association with a transient resurgence in P4 than in heifers with a progressive P4 decrease. The hypothesis that repeated E2 exposure stimulates increasing prominence of PGFM pulses was not supported. Instead, repeated exposure reduced the prominence of PGFM pulses, in contrast to the stimulation from the first E2 treatment. Reduced prominence of a PGF(2α) pulse during luteolysis can lead to a transient resurgence in P4 concentration.

Effect of dose of estradiol-17β on prominence of an induced 13,14-dihydro-15-keto-PGF(2α) (PGFM) pulse and relationship of prominence to progesterone, LH, and luteal blood flow in heifers

Various doses of estradiol-17β (E(2)) were used in heifers to induce a pulse of 13,14-dihydro-15-keto-prostaglandin F(2α) (PGFM). The effect of E(2) concentration on the prominence of PGFM pulses and the relationship between prominence and intrapulse concentration of progesterone (P(4)), LH, and luteal blood flow were studied. A single dose of 0 (vehicle), 0.01, 0.05, or 0.1 mg of E(2) was given (n = six/group) 14 d after ovulation. Blood samples were collected, and luteal blood flow was evaluated hourly for 10 h after the treatment. The 0.05-mg dose increased and the 0.1-mg dose further increased the prominence of the induced PGFM pulse, compared with the 0.0-mg dose and the 0.01-mg dose. The PGFM pulses were subdivided into three different prominence categories (<50, 50 to 150, and >150 pg/mL at the peak). In the 50 to 150 category, P(4) concentration increased (P < 0.05) between -2 h and 0 h (0 h = peak of PGFM pulse). In the >150 category, P(4) decreased (P < 0.05) between -1 h and 0 h, LH increased (P < 0.05) at 1 h, and luteal blood flow apparently decreased (P < 0.05) at 2 h of the PGFM pulse. The novel results supported the following hypotheses: (1) an increase in E(2) concentration increases the prominence of a PGFM pulse, and (2) greater prominence of a PGFM pulse is associated with a greater transient intrapulse depression of P(4) at the peak of the PGFM pulse. In addition, the extent of the effect of prostaglandin F(2α) on the increase in LH and changes in blood flow within the hours of a PGFM pulse was related positively to the prominence of the PGFM pulse.

Effect of luteinizing hormone oscillations on progesterone concentrations based on treatment with a gonadotropin-releasing hormone antagonist in heifers

Close temporality has been reported between the episodic secretion of luteinizing hormone (LH) and progesterone (P4) during the midluteal phase and preceding the beginning of luteolysis in cattle. In the present studies, the relationship between LH and P4 was examined by blocking LH oscillations with the gonadotropin-releasing hormone (GnRH) antagonist, acyline. In a titration study, the minimal single acyline dose for blocking LH oscillations in heifers was 3 μg/kg. The main experiment compared LH and P4 concentrations and oscillations between a group treated with acyline on day 15 after ovulation (n = 8) and a control group (n = 4). Concentrations of P4 in blood samples collected every 8 h on days 13 to 18 indicated that acyline treatment did not alter the time that luteolysis began or the length of the luteolytic process. In blood samples collected every hour for 24 h beginning at the hour of treatment, acyline reduced the LH concentrations and blocked LH oscillations. The hourly LH means were 0.06 to 0.08 ng/mL, comparable to the mean concentration at the nadirs of LH oscillations in controls (0.07 ng/mL). During the hourly sampling, the GnRH antagonist produced the following P4 responses: (1) lower P4 concentrations, (2) fewer and reduced prominence of P4 oscillations, and (3) increased length and variability in the interval between the peaks of P4 oscillations. Results indicated that LH oscillations affect both the prominence and the rhythmicity of P4 oscillations during preluteolysis but not the onset and length of luteolysis.

Concomitance of luteinizing hormone and progesterone oscillations during the transition from preluteolysis to luteolysis in cattle

The temporal relationships of episodes of luteinizing hormone (LH) oscillations, 13,14-dihydro-15-keto-PGF2α (PGFM) pulses, and progesterone (P4) fluctuations during the latter portion of preluteolysis and the early portion of luteolysis were characterized. In Experiment 1, the detection of LH episodes in blood samples collected every 15 min for 8 h was compared with detection in the samples collected every hour in 4 heifers. The number of independently detected episodes/heifer (total = 7) was the same for the 15-min and hourly collection intervals. In Experiment 2, blood samples were collected every hour (n = 7 heifers) and retrospectively assigned to 15 h before and 15 h after the transitional hour between preluteolysis and luteolysis. During preluteolysis, compared with luteolysis, the amplitude of LH oscillations was greater (0.28 ± 0.03 vs 0.18 ± 0.03 ng/mL; P < 0.02) and the interval between peaks of LH oscillations was shorter (3.3 ± 0.3 h vs 4.3 ± 0.6 h; P < 0.04). The LH peaks occurred at the same hour as the peak of a P4 fluctuation in 77% and 29% of LH oscillations (P < 0.0009) during preluteolysis and luteolysis, respectively. In preluteolysis, synchrony between LH and P4 episodes occurred consistently during the P4 rebound after the peak of a PGFM pulse. In luteolysis, the LH peak preceded the peak of the P4 rebound. On a temporal basis, the hypothesis was supported that episodic LH accounts, at least in part, for the reported P4 rebound that occurs after the P4 suppression at the peak of a PGFM pulse.