Intraovarian effect of dominant follicle and corpus luteum on number of follicles during a follicular wave in heifers

Use of color-Doppler ultrasonography for selection of recipients in timed-embryo transfer programs in beef cattle

We aimed to study the association between CL characteristics assessed by color-Doppler ultrasonography (Doppler-US) at the time of embryo transfer (ET) and pregnancy rate (P/ET) in beef recipients. Estrous cycles of crossbred beef recipients were synchronized for timed-ET. On the day of ET (Day 7), CL area, proportion of luteal blood perfusion (BP), and the relationship between the largest dominant follicle (DF) and CL (ipsilateral or contralateral) were determined. Animals (n = 444) received an in vitro produced embryo from Nelore donors, placed in the uterine horn ipsilateral to the CL. Recipients were split retrospectively in three subgroups according to CL area [small (<3 cm²), medium (3-4 cm²), or large (>4 cm²)] and three subgroups according to luteal signals of BP [low (≤40%), medium (45-50%) or high (≥55%)]. Pregnancy was detected on Days 30-45 by transrectal ultrasonography and P/ET was analyzed considering the effects of cow's category (suckling or non-suckling), CL area, luteal BP and side of DF. P/ET increased along with BP category [low, 45.9%^B, (62/135); medium, 54.1%^AB (93/172); and high, 58.4%^A (80/137)]. When luteal BP was evaluated as a continuous variable, a significant (P < 0.05) linear and positive effect was observed on P/ET. A greater (P < 0.05) CL area and serum progesterone concentrations were observed in the medium and high BP than in the low BP category. Although an effect of luteal size category was not significant on P/ET [small, 49% (76/155); medium, 59.7% (83/139); and large, 50.7% (75/148); P > 0.1], when CL area was evaluated as a continuous variable, a quadratic effect (P < 0.05) indicated a positive relationship between P/ET and CL area until luteal tissue reached 4.07 cm², followed by a negative relationship. The location of the first-wave DF in relation to the CL did not affect P/ET (P > 0.1). In conclusion, Doppler-US is an innovative tool that has the potential to be used for selection of suitable embryo recipients based on luteal BP. Selection of recipients that have a greater chance of maintaining pregnancy will increase the success of timed-ET programs.

Role of intraovarian mechanisms and side of ovary on characteristics of follicle selection in Bos taurus heifers

Intraovarian effects on diameter of future dominant follicle (DF or F1) and future largest subordinate follicle (F2) during the few days before selection of the future DF and subordinate follicles were studied in 147 bovine interovulatory intervals. Follicle selection involves diameter deviation or the beginning of separation of growth rates between F1 and F2. Diameter deviation is classified as conventional (F2 ≥ 7.0 mm when F1 is 8.5 mm or at expected deviation) and as undersized (F2 < 7.0 mm when F1 is 8.5 mm). Diameter separation of F1 and F2 in conventional and undersized deviations is characteristically abrupt and gradual, respectively. The predeviation diameter of F2 when located in an ovary that later becomes the F1 intraovarian patterns of DF-CL, devoid (ovary without a DF or CL), DF alone, or CL alone and in left or right ovaries (LO, RO) was compared between conventional and undersized deviations. In conventional deviation, ovaries with the future DF (combined DF-CL and DF patterns) were associated with greater (P < 0.02) predeviation growth rate of F2 when the DF was in the right ovary (DF/RO, 1.6 ± 0.1 mm/d) than when in the left ovary (DF/LO, 1.2 ± 0.1 mm/d). The F2 was in DF/RO more frequently (75%, P < 0.002) than in non-DF/RO. When F2 was in the future devoid F1 pattern and F1 was 6 mm, F2 was smaller (P < 0.002) in the undersized class (5.3 ± 0.2 mm) than in the conventional class (6.3 ± 0.1) but not when F2 was in one of the other future F1 patterns. Only the devoid pattern was greater in frequency (P < 0.03) in the undersized class than in the conventional class. The novel hypothesis was supported that location of F2 in ovaries with different future F1 intraovarian patterns and on different sides affects the predeviation diameter and growth rate of F2 and thereby the frequencies of conventional and undersized deviations during follicle selection.

Effects of plane of nutrition and arginine on ovarian follicles in non-pregnant sheep: Cell proliferation, and expression of endothelial nitric oxide and its receptor

The aim of this study was to investigate the role of the nitric oxide (NO) system in ovarian function, by determining if arginine (Arg) supplementation impacts follicle number, cell proliferation, and expression of the NO system members in nutritionally compromised ewes. Ewes were randomly assigned into maintenance (C, 100% requirements), excess (O; 2xC), or restricted (U; 0.6xC) diets 8 weeks prior to Arg treatment. Ewes were individually fed twice daily with pelleted diets. Ewes from each nutritional group were randomly assigned to one of two treatments: saline or Arg, which was initiated on day 0 of the estrous cycle and administered 3 times per day. Ovaries were collected at the early-luteal, mid-luteal and late-luteal/follicular phases of the estrous cycle to determine 1) the number of surface follicles, 2) follicle cell proliferation marked by Ki67 protein expression, and 3) expression of endothelial nitric oxide (eNOS; NOS3) and soluble guanylyl cyclase beta (sGC; GUCY1B3) protein and mRNA in granulosa (G) and theca (T) layers using immunohistochemistry followed by image analysis and qPCR, respectively. During nutritional treatment, C maintained body weight, O gained 6±1.2 kg, and U lost 14±1.3 kg. Our data show that: 1) Ki67 was expressed in all ovarian compartments, eNOS protein was detected in blood vessels of T and stroma, and sGC protein was detected in T cells, and blood vessels of T layer and other ovarian compartments; 2) plane of nutrition affected the number of surface follicles, and thus folliculogenesis, cell proliferation in the T layer, eNOS and sGC protein expression in T, and NOS3 and GUCY1B3 mRNA expression in G; 3) Arg treatment affected cell proliferation in G and T, eNOS and sGC protein expression in T, mRNA expression of NOS3 in T in all groups, and GUCY1B3 in G depending on the stage of the estrous cycle; and 4) G and T cell proliferation, and expression of eNOS and sGC protein in T was affected by the stage of the estrous cycle. Our data demonstrated that plane of nutrition and Arg are involved in the regulation of follicular functions in non-pregnant sheep.

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.

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.