Subordinate Follicles Research Articles

Control and regulation of folliculogenesis--a symposium in perspective.

The Intervet Symposium 'Control and Regulation of Folliculogenesis' took place at the Annual Conference of the Society for the Study of Fertility in University College, Dublin in July, 1995. Five papers were presented, of which abstracts have been published. Discussion centred on monotocous species and principally addressed the question 'How is the ovulatory follicle selected and nurtured?' Many follicles start to develop simultaneously, but most become atretic. During the luteal phase of the cycle, several waves of follicles are initiated, and although one in each wave gains dominance, all ultimately atrophy. The dominant follicle in the wave produced towards the end of the luteal phase ovulates. The biochemical characteristics of dominant and subordinate follicles were contrasted, and the endocrine environment in which they waxed and waned was analysed. Interaction of autocrine and paracrine effectors, principally with FSH, LH and their receptors, ultimately determines follicular destiny.

Control and regulation of folliculogenesis--a symposium in perspective

The Intervet Symposium 'Control and Regulation of Folliculogenesis' took place at the Annual Conference of the Society for the Study of Fertility in University College, Dublin in July, 1995. Five papers were presented, of which abstracts have been published. Discussion centred on monotocous species and principally addressed the question 'How is the ovulatory follicle selected and nurtured?' Many follicles start to develop simultaneously, but most become atretic. During the luteal phase of the cycle, several waves of follicles are initiated, and although one in each wave gains dominance, all ultimately atrophy. The dominant follicle in the wave produced towards the end of the luteal phase ovulates. The biochemical characteristics of dominant and subordinate follicles were contrasted, and the endocrine environment in which they waxed and waned was analysed. Interaction of autocrine and paracrine effectors, principally with FSH, LH and their receptors, ultimately determines follicular destiny.

Aspiration of the dominant follicle in mares and its effect on subsequent follicular development

An attempt was made to increase the number of small- and medium-sized follicles present for ultrasound-guided oocyte recovery by aspirating the dominant follicle prior to its inhibition of growth of other follicles. Cyclic mares were randomly assigned to one of four groups on day of ovulation. Each mare was examined daily with ultrasound beginning 8 days after ovulation to determine growth and regression of individual follicles at least 15 mm in diameter. Once a dominant follicle was identified, the dominant follicle in Group 1 mares was aspirated and all other follicles (at least 15 mm) aspirated 3 days later; the dominant follicle in Group 2 mares was identified but not aspirated and all follicles (at least 15 mm) aspirated 3 days later; the dominant follicle in Group 3 mares was aspirated and all other follicles (at least 15 mm) aspirated 6 days later; and the dominant follicle in Group 4 mares was identified but not aspirated and all follicles (at least 15 mm) aspirated 6 days later. A dominant follicle was defined as the largest follicle present for 2 consecutive days beginning 8 days after ovulation. Identification did not occur until the dominant follicle was at least 25 mm in diameter. The dominant follicle was identified 15.1 ± 3.4 days after ovulation. Mean number of small (3–17 mm) and medium (18–27 mm) sized follicles 3 or 6 days after identification/aspiration of the dominant follicle were similar among all treatment groups ( P > 0.05). Mares in Group 2 had a greater ( P < 0.05) number of large follicles (at least 28 mm) 3 days after identification of the dominant follicle than Group 1 mares (1.3 vs. 0.5, respectively); means for Groups 3 and 4 were similar. Based on linear regression slopes of growth patterns for individual follicles, a higher rate of atresia occurred in subordinate follicles within 6 days following identification, but no aspiration of the dominant follicle (−0.63 mm day −1), than for those follicles present following aspiration of the dominant follicle (−0.10 mm day −1, P < 0.05). A greater percentage of follicles were growing (+ slope) after aspiration of the dominant follicle ( 47 137 or 34.3%) than those follicles present without aspiration of the dominant follicle ( 15 133 or 11.3%, P < 0.05). In summary, aspiration of the dominant follicle did not increase the number of small- or medium-sized follicles 3 or 6 days later. However, a smaller proportion of follicles underwent atresia following aspiration of the dominant follicle compared with those follicles present with the dominant follicle still intact. Minimizing the number of subordinate follicles undergoing atresia may be a benefit for recovering viable oocytes from these follicles.

Effect of season on follicular dynamics and plasma concentrations of estradiol-17β, progesterone and luteinizing hormone in lactating Holstein cows

Lactating Holstein cows (n=16), averaging 64.1 d in milk, were utilized over 4 replicate months (April, June, August and November) in a shade management system to examine the effects of season on follicular dynamics and plasma concentrations of estradiol (E2), progesterone (P4) and luteinizing hormone (LH). Cows were synchronized to estrus using a combination of Buserelin (GnRH, 8 ug) and prostaglandin F2α (PGF2α, 25 mg) given 7 d apart. Follicular development was monitored daily by ultrasonography, and plasma concentrations of E2, P4 and LH measured by radioimmunoassay. The replicate month had no detectable effects on estrus interval (3.1 ± 0.3 d) or percentage of cows (78.1 ± 9.4%) that expressed estrus following GnRH and PGF2α treatment. Preovulatory follicles grew at faster rates (P<0.01) in June (2.0 ± 0.6 mm/d), than in April (1.1 ± 0.6 mm/d), August (1.0 ± 0.6 mm/d) or November (1.2 ± 0.6 mm/d). First wave dominant follicles were consistently larger in April than in June, August and November. The larger and more persistent size of the first wave dominant follicle in April was associated with an earlier regression of the largest subordinate follicle and a sharper decrease in the number of medium size follicles (6 to 9 mm) by Day 9 of the estrous cycle. Conversely, growth of the first wave dominant follicle was slower and the largest subordinate follicle was more persistent in August than in April, June or November. The proestrous rise in plasma E2 occurred faster (P<0.01) in August (10.1 ± 2.1 pg/d) than in April (4.6 ± 2.1 pg/d), June (5.3 ± 2.1 pg/d) or November (5.9 ± 2.1 pg/d). Concentrations of P4 in plasma increased and reached higher (P<0.01) luteal values in August (15.1 ± 0.6 ng/ml) and November (16.0 ± 0.6 ng/ml) than in April (6.1 ± 0.6 ng/ml) and June (10.6 ± 0.6 ng/ml). There was no detectable effect of month on LH pulse characteristics 48 h post-PGF2α. The maximum size of the corpus luteum (CL) was greatest in November and was related positively to diameter of the ovulatory follicle of the preceding cycle. Results indicated that ovarian follicular development and dominance may be altered during summer months. However, it is uncertain whether these changes can be related to the well-documented low breeding efficiency during warmer months of the year in subtropical environments.

Oocyte structure in dominant and subordinate follicles in zebu cattle (Bos indicus).

The objective of the study was to investigate the light and ultrastructural morphology of dominant and subordinate oocytes from zebu (Bos indicus) cattle. Healthy cycling animals, which had a well-developed corpus luteum as judged by rectal palpation, were administered cloprostenol to induce luteolysis and therefore ovulation. The animals were slaughtered at days 3-11 post-ovulation, but those slaughtered at days 8-11 received a second injection of cloprostenol at day 7. Cumulus-oocyte complexes were aspirated from the largest (dominant) and the second largest (subordinate) follicles, and processed for transmission electron microscopy. Up to day 7, the dominant oocyte presented a peripherally located spherical oocyte nucleus with a compact dense fibrillar nucleolus. After day 7, the nuclear envelope became undulated and the nucleolus vacuolated. The nuclei contained an average of four nucleoli. In addition to vesicles, mitochondria, smooth endoplasmic reticulum, Golgi complexes and cortical granules, the ooplasm contained annulate lamellae and microtubules. Moreover, mitochondrial granules and pleomorphic forms of mitochondria were commonly observed. Some subordinate oocytes exhibited advanced stages of meiotic maturation. It is concluded that (1) the dominant oocyte undergoes certain prematurational changes, including nucleolus vacuolation, in the period from luteolysis up to the presumptive occurrence of the LH peak and (2) subordinate oocytes may undergo meiotic maturation.

Follicular and hormonal development in prepubertal heifers from 2 to 36 weeks of age

The aim of this study was to characterize changes in ovarian follicle dynamics in relation to changes in hormone secretion in heifer calves from birth to 8 months of age. The position and diameter of ovarian follicles > or = 4 mm in diameter were recorded, the number of ovarian follicles > or = 2 mm in diameter counted, and blood samples collected daily for periods of 18 days, starting at 2, 8, 14, 24 and 34 weeks of age in ten heifers. The mean age at first ovulation was 52.8 +/- 1.6 weeks. At all ages ovarian follicular development occurred in a wave-like manner, as in mature cattle. The maximum diameter of the dominant and the largest subordinate follicles increased between 2 and 34 weeks of age (P < 0.05); however, the greatest increase occurred between 2 and 8 weeks of age. There was a similar increase in the numbers of small and large ovarian follicles (P < 0.05). The duration of detection of dominant follicles (number of days visible at a diameter of > or = 4 mm) also increased between 2 and 34 weeks of age (P < 0.05). The emergence of waves of follicular development was preceded by peaks in plasma FSH concentrations (P < 0.05) at 2 weeks of age but this was less clear at other ages. There was a rise in circulating concentrations of gonadotrophins between 4 and 14 weeks of age. We concluded that in heifer calves as young as 2 weeks of age ovarian follicles grew in a wave-like fashion, similar to those of adult cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Infrequent structures in cattle oocytes

Uncommon and controversial structures in cattle oocytes were studied in dominant and subordinate follicles of unstimulated Bos taurus and zebu (Bos indicus), and in FSH-stimulated B. taurus cattle, before or after administration of cloprostenol. Growing oocytes were very rare in follicles more than or equal to 5 mm in diameter. For the first time, special vesicles that may be involved in cortical granule synthesis were observed. Classical rough endoplasmic reticulum was very rare in unstimulated oocytes, but was seen at superovulation. Vacuolation of the nucleolus was a common feature in dominant oocytes that were collected after cloprostenol injection, except in superovulated cattle. Annulate lamellae were very rare or absent in oocytes of B. taurus, while they were more frequent in zebu oocytes.

Oocyte morphology in dominant and subordinate follicles

The structure of oocytes aspirated from the dominant and its subordinate follicles was investigated from the achievement of follicular dominance to ovulation. Ovulation was induced in 18 heifers and 5 cows by injection of cloprostenol at days 8-14 (day 0 = day of ovulation), and follicular development was monitored by ultrasonography. The animals were slaughtered at days 3-11, but animals slaughtered on days 8-11 were given a second injection of cloprostenol at day 7 to allow ovulation of the dominant follicle of the first follicular wave. Oocytes were aspirated from the dominant (largest) and two largest subordinate follicles and processed for transmission electron microscopy, whereas the follicular fluids were analyzed for concentrations of estradiol-17 beta (E2) and progesterone (P4). Dominant follicular growth was associated with increase in the concentration of E2 and P4 in the follicular fluid, which was E2-dominated. From days 3-7, the dominant oocytes had pronounced junctional contacts with the cumulus cells and a nonundulating nuclear envelope but showed an increase in the number of lipid droplets and a decrease in the size of Golgi complexes, the size of cortical granule clusters, and the number of microvilli stacks. After cloprostenol injection on day 7, but before the anticipated LH surge, the dominant oocytes showed a reduced oocyte-cumulus contact, vacuolization of the nucleolus, undulation of the nuclear envelope, and dispersal of the mitochondrial clusters. The morphological alterations occurring in the dominant oocytes before the anticipated LH surge are suggested to be a prerequisite for the oocyte to achieve the competence to undergo final maturation. Subordinate follicles ceased growing at about days 3-4 and their follicular fluid had low E2:P4 ratio or was P4-dominated. Subordinate oocytes displayed degenerative features in their cumulus investment and nuclear activation and maturation especially after day 5. The structural changes associated with oocyte degeneration showed similarities with the processes seen before and during final maturation of the dominant oocytes.

Effect of somatotropin and/or equine chorionic gonadotropin on serum and follicular insulin-like growth factor I and insulin-like growth factor binding proteins in cattle.

We investigated the effect of administration of somatotropin (ST) and/or eCG on insulin-like growth factor I (IGF-I) and IGF-binding proteins (IGFBP) in serum and follicular fluid (FFL) of cattle actively immunized against growth hormone-releasing factor (GRF). Cyclic beef cattle, previously immunized against GRF-(1-29)-Gly-Gly-Cys-NH2 conjugated to human serum albumin (synthesized and provided by Hoffmann-LaRoche, Inc., Nutley, NJ; GRFi, n = 31) or to human serum albumin alone (HSAi, n = 26), received (i.m.): 1) 25 mg recombinantly derived methionyl somatotropin (rbST, n = 14; sometribove provided by Monsanto Co., St. Louis, MO); 2) 1100 IU eCG (n = 10); 3) rbST and eCG (rbST-eCG, n = 15); or 4) vehicle (VEH, n = 17) at 0 and 24 h after receiving prostaglandin F2 alpha (PGF2 alpha). Serum samples were collected at 0 and 40 h after PGF2 alpha, and the ovary bearing the largest follicle (DOM) was removed 44.0 +/- 0.5 h after PGF2 alpha; FFL was harvested from DOM and the subordinate follicle (SUB). Before treatment (0 h), GRFi cows had lower serum ST (0.6 +/- 0.2 vs. 2.2 +/- 0.2 ng/ml; p < 0.01) and IGF-I (26 +/- 4 vs. 72 +/- 4 ng/ml; p < 0.01), but greater IGFBP-2 (594 +/- 48 vs. 384 +/- 52 ng/ml; p < 0.01) than HSAi cows. Serum and FFL concentrations of IGF-I or IGFBP-2 were not different between rbST- and rbST-eCG-treated cows or between VEH- and eCG-treated cows at Hour 40 after the initial treatment injection; therefore, data were combined and designated as rbST and VEH, respectively. Serum IGF-I was increased to a greater extent (percentage increase above 0 h) by rbST treatment in GRFi (362 +/- 24) than in HSAi (176 +/- 16) cows (immunization by treatment, p < 0.01). Across GRFi and HSAi, rbST lowered serum IGFBP-2 (342 +/- 31 vs. 541 +/- 27 ng/ml, rbST vs. VEH; p < 0.01). Diameters of DOM or SUB were not affected by immunization or treatment. Concentrations of IGF-I and IGFBP-3 (determined by ligand blot analysis) in FFL from both DOM and SUB were lower (p < 0.05) in GRFi than in HSAi cows. In contrast, IGFBP-2 in FFL was elevated in SUB, but not DOM, in GRFi compared to HSAi cows.(ABSTRACT TRUNCATED AT 400 WORDS)

Follicular waves and circulating gonadotrophins in 8-month-old prepubertal heifers

Eleven age-matched (+/- 4 days) Hereford heifers were examined by transrectal ultrasonography daily for 18 days beginning 20 weeks (5 months) before puberty (first ovulation) to determine the suitability of the transrectal ultrasound technique for imaging the ovaries of prepubertal heifers and to test the hypothesis that ovarian follicular development occurs in waves in prepubertal heifers. Satisfactory ovarian images were obtained during preliminary ultrasound examinations conducted 4 weeks before the observational period (that is 32 weeks of age), during which a semirigid probe extension was used to allow external manipulation of the intrarectally placed ultrasound transducer. Daily examinations commencing at 36 weeks of age were accomplished by intrarectal placement of the operator's hand and transducer, without complication, in all 11 heifers throughout the observational period. Periodic increases in the number of follicles detected (day effect, P < 0.02) were inversely related to the diameter of the largest follicle (r = -0.3, P < 0.03). Portions of three anovulatory follicular waves were detected in all heifers during the observational period (first and third waves in part and second wave in whole). Individual follicles destined to assume a dominant or subordinate position in a wave were retrospectively identified and monitored beginning at a diameter of 4-5 mm. The interval between the emergence of dominant follicles of successive waves (interwave interval) was 8.0 +/- 0.4 days and the interval between successive maxima in the number of follicles per heifer per day was 8.1 +/- 0.5 days. The growing phase of the dominant follicles best fit a quadratic curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular dynamics during the bovine estrous cycle: A limiting factor in improvement of fertility?

The use of ultrasonographic techniques for visualizing bovine ovaries has elucidated patterns of follicular development in cattle and provided some insight into the regulation of follicular growth and development. In cattle the development of large antral follicles occurs in waves that consist of the contemporaneous appearance of around three to six follicles 5 mm or more in diameter. Over several days one follicle grows larger than the others and is selected to become the dominant follicle, while the smaller subordinate follicles regress. The dominant follicle appears to regulate the growth of subordinate follicles, since the appearance of the next wave is accelerated if the dominant follicle is destroyed and delayed if the lifespan of the dominant follicle is prolonged experimentally. Follicular waves occur regularly when plasma gonadotropin concentrations are basal and the number of waves per cycle is correlated with cycle length. There is evidence that subtle changes in hormonal milieu regulate the pattern of waves. Waves are preceded by small increases in plasma follicle stimulating hormone (FSH) and natural or experimentally induced decreases in basal FSH are associated with the demise of the dominant follicle. Increases in luteinizing hormone (LH) pulse frequency are observed during prolonged development of dominant follicles. Although the mechanisms that promote the selection of a dominant follicle have not been elucidated, the results reviewed in this paper make it clear that a great deal of progress has been made in understanding patterns of follicular development and their regulation. These advances have provided insight into some of the limitations of current methods for regulating bovine fertility, interesting experimental models for future studies, and information that may be used for improving reproductive efficiency in cattle.

Effect of the dominant follicle on regression of its subordinates in heifers

The relationship between a dominant follicle of a follicular wave and the suppression of subordinate follicles was studied during the first postovulatory wave (Wave 1) in Holstein heifers. The dominant follicle (largest follicle) was cauterized or a sham-operation was done on day 3 (day 0 = ovulation) using seven heifers per group. In the cautery group, compared to the controls, the largest subordinate follicle attained a larger diameter (11 7 vs 8 0 mm; P &lt; 0.01), reached maximum diameter at a later day (day 9.2 vs. day 3.1; P &lt; 0 01) and began to regress at a later day (day 14.3 vs. day 5.7; P &lt; 0.01). In addition, the emergence of Wave 2 was hastened (day 6.4 vs. day 9.3; P &lt; 0.05) and more heifers had more than two waves per interovulatory interval (5 of 6 vs. 2 of 7; P &lt; 0.05). In heifers with the dominant follicle eliminated, the largest subordinate grew to the diameter of a dominant follicle during Wave 1 (n = 3) or became the dominant follicle of a newly emerged wave (n = 2). A subordinate sometimes persisted as a small follicle (e.g., 5 mm) for several days before resurging. However, it was not convincingly demonstrated that a subordinate follicle could resurge after it had begun to regress (decrease in diameter). Results supported the hypothesis that suppression of subordinate follicles is a prolonged process, so that resurgence of a subordinate can occur if the dominant follicle is removed. Key words: Ovaries, follicular waves, selection, cattle, cauterization

Effect of environmental heat stress on follicular development and steroidogenesis in lactating Holstein cows

Lactating Holstein cows were utilized over two replicate periods (July and September, 1990) to examine the effect of summer heat stress on follicular growth and steroidogenesis. On day of synchronized ovulations, cows were assigned to shade (n=11) or no shade (n=12) management systems. Follicular development was monitored daily by ultrasonography until ovariectomy on Day 8 post estrus. At time of ovariectomy, dominant and second largest follicles were dissected from the ovary. Aromatase activity and steroid concentrations in dominant and subordinate follicles were measured. Acute heat stress had no effects on patterns of growth of first wave dominant and subordinate follicles between Days 1 and 7 of the cycle. Compared with shaded cows, the heat stressed cows did not have suppression of medium size (6 to 9 mm) follicles between Days 5 and 7. A treatment × follicle interaction was detected (P<0.01) for follicular diameter and fluid volume at Day 8. Dominant follicles in shade were bigger (16.4>14.5 mm) and contained more fluid (1.9>1.1 ml) than dominant follicles in no shade. Conversely, subordinate follicles in no shade were bigger (10.1>7.9 mm) and contained more fluid (0.4>0.2 ml) than subordinate follicles in shade. Concentrations of estradiol in plasma and follicular fluid were higher (P<0.01) in July than in September. Heat stress appears to alter the efficiency of follicular selection and dominance, and to have adverse effects on the quality of ovarian follicles.

Relationships between FSH surges and follicular waves during the estrous cycle in mares

Individual follicles ≥15 mm were monitored daily by ultrasonography in 12 mares during the estrous cycle. Follicular waves were designated as major waves (primary and secondary) and minor waves based on maximum diameter of the largest follicle of a wave (major waves, 34 to 47 mm; minor waves, 18 to 25 mm). Dominance of the largest follicle of major waves was indicated by a wide difference (mean, 18 mm) in maximum diameter relative to the second largest follicle. Dominant follicles of primary waves (n=12) emerged (attained 15 mm) at a mean of Day 12 and resulted in the ovulations associated with estrus (ovulation=Day 0). The dominant follicle of a secondary wave (n=1) emerged on Day 2 and subsequently ovulated in synchrony with the dominant follicle of the primary wave, which emerged on Day 9. The largest follicles of minor waves (n=4) emerged at a mean of Day 5, reached a mean maximum diameter 3 days later, and subsequently regressed. There was a significant increase in mean daily FSH concentrations either 6 days (primary wave) or 4 days (minor waves) before the emergence of a wave. Mean concentrations of FSH decreased significantly 2 days after emergence of the primary wave. Divergence between diameter of the dominant and largest subordinate follicle of the primary wave was indicated by a significantly greater mean diameter of the dominant follicle than of the largest subordinate follicle 3 days after wave emergence and by the cessation of growth of the largest subordinate follicle beginning 4 days after the emergence of a wave. Surges of FSH were identified in individual mares by a cycle-detection program; surges occurred every 3 to 7 days. Elevated mean FSH concentrations over the 6 days prior to emergence of the primary wave was attributable to a significantly greater frequency of individual FSH surges before wave emergence than after emergence and to an increase in magnitude of peak concentrations of FSH associated with individual surges.

Ovarian Follicular Populations in Lactating Dairy Cows Treated with Recombinant Bovine Somatotropin (Sometribove) or Saline and Fed Diets Differing in Fat Content and Energy

Interactions of dietary energy and fat with recombinant bST (sometribove) injections were tested for their effects on ovarian function. Lactating dairy cows were fed one of three diets differing in energy concentration (NEL) and percentage of DM of calcium salts of long-chain fatty acids: diet 1, 1.68 Mcal/kg and 0%; diet 2, 1.68 Mcal/kg and 2.2%; and diet 3, 1.78 Mcal/kg and 2.2%. Cows were injected daily with bST or saline during one of two 19-d interestrous periods (crossover design) in which ovarian follicles were measured by ultrasonography. The bST-treated cows produced more FCM and were in lower energy balance than saline-treated cows. Before d 12 (first follicular wave, estrus = d 0), bST-treated cows had more ovarian follicles in classes 1 (3 to 5mm; cows on diet 3) or 2 (6 to 9mm; cows on diets 1 and 2) than saline-treated cows. After d 12 (preovulatory follicular wave), numbers of follicles in different size classes were similar for bST-treated and saline-treated cows, but cows fed diet 2 had larger preovulatory follicles. Lower dietary energy and bST treatment were both associated with larger subordinate follicles. Ovarian follicles less than 10mm were stimulated by bST, and calcium salts of long-chain fatty acids increased diameters of preovulatory follicles.

A method for characterizing ultrasonically-derived follicular data in heifers

A method was developed for ultrasonically characterizing follicular waves in heifers without the necessity of maintaining day-to-day identities of individual follicles (nonidentity method). Results were compared to a method in which the identities of individual follicles were maintained from day to day (identity method). Data collected daily during 5 estrous cycles were processed by each method, independently, by different operators. The nonidentity method involved grouping and then profiling follicles in order of decreasing diameters without regard to day-to-day identities. The profiling scheme distinguished between follicles of the left versus the right ovary. The dominant and subordinate follicles were readily distinguishable in the nonidentity profiles. When successive dominant follicles developed in the opposite ovary, the follicles were profiled directly. When two successive dominant follicles developed on the same ovary, size information was obscured for a few days where the profiles for each follicle crossed, but continuity of the profiles on each side of the area of ambiguity was maintained. The nonidentity method seemed equivalent to the identity method in determining characteristics of the dominant follicle (e.g., maximal diameter, growth rate, regression rate). Day of emergence of a wave and day of divergence in diameters between dominant and subordinate follicles were readily determined by inspection of the nonidentity profiles. A greater number of subordinate follicles per wave was detected by the nonidentity method due to the inability to individually identify all detected follicles by the identity method. Regression of follicles from a previous wave into the subordinate follicles of a succeeding wave was apparent by either method. The nonidentity method seemed suitable for most needs, was less tedious, and required less skill than the identity method.

Ovarian Activity in Ultrasound Image and Milk Progesterone Concentration in Postpartum Dairy Cows

Dolezel, R., K. Karl berg, E. Ropstad: Ovarian Activity in Ultrasound Image and Milk Progesterone Concentration in Postpartum Dairy Cows. Acta vet. Bmo, 62, 1993: 173-178. Eighteen pluriparous dairy cows were ultrasonographically observed twice a week from day 9-10 post partum to the 2nd ovulation. Milk samples were taken three times a week and progesterone was assayed by RIA. Before the 1st postpartum ovu­ lation and during the 1st sexual cycle, 1.09 ± 1.09 and 1.8 ± 1.11, respectively, subordinate follicles and 1.5 ± 0.52 and 2.4 ± 0.72, respectively, follicular waves were found. The 1st ovulation occurred 17.9 ± 5.04 days after parturition, the length of the 1st sexual cycle was 19.4 ± 4.66 days and clinical involution of the uterus was completed 22.6 ± 4.34 days after parturition. The period from parturition to the time of the 1st postpartum ovulation and the length of the 1st sexual cycle were positively correlated with the number of follicular waves during the periods. About 81 % of the first postpartum follicular waves and 88 % of the 1st ovulations occurred in the ovary contralateral to the previous pregnant uterine hom. The differences disappeared after the 1st postpartum ovula­ tion. Average values of milk progesterone were discovered during the 1st and 2nd sexual cycles at day 5-7 (5.9 ± 4.78 and 6.3 ± 5.16ng/ml) and at day 10-12 (5.6 ± 5.83 and 11.4 ± 7.74 ng/ml).

Selection of a dominant follicle and suppression of follicular growth in heifers

The following aspects of follicle-stimulating hormone (FSH)-follicular relationships were studied in heifers: (1) the role of the decline in circulating levels of FSH in selection of a dominant follicle of a follicular wave; (2) the relationship of an FSH nadir (low levels between surges) to the absence of development of new follicles of a detectable diameter during the interim between the emergence of successive waves. A recombinant DNA-derived bovine FSH was used. Administration of bovine follicle-stimulating hormone (bFSH) for two days before the time of selection of the dominant follicle of the first post-ovulatory follicular wave delayed the time of divergence of the follicles into dominant and subordinates (first significant divergence: bFSH treatment before selection, Day 4.0; bFSH treatment after selection, Day 2.5; controls, Day 2.5: ovulation, Day 0). Significantly greater growth of the first and second largest subordinates occurred in the pre-selection group. A superovulatory dose of bFSH for 4 days with PGF 2α-induction of luteolysis resulted in multiple ovulations when begun on Day 1 (before the expected time of follicle divergence; mean 2.8 ovulations per heifer) than when begun on Day 5 (after divergence; mean 1.0 ovulation per heifer). Administration of bFSH during the expected time (Days 5 and 6) of an FSH nadir did not alter the day of detectable emergence of the next follicular wave. Results supported the following hypotheses: (1) a decline in the wave-stimulating FSH surge is an integral component of the selection mechanism that results in the divergence into dominant and subordinate follicles; (2) the nadir between FSH surges does not account directly for the absence of the development of new follicles between the emergence of waves.

Oocyte morphology in dominant and subordinate follicles during the first follicular wave in cattle

Oocyte morphology in dominant and subordinate follicles during the first follicular wave in cattle

The effect of recombinant bovine somatotrophin on ovarian follicular growth and development in heifers

The effects of recombinant bovine somatotrophin (BST) on the dynamics of ovarian follicular growth and development and peripheral insulin concentrations were investigated. Initially, studies were carried out in a population of Hereford x Friesian heifers to validate the ultrasound technique. In the first experiment, 12 heifers were injected daily with either 25 mg BST or vehicle for two oestrous cycles, and the effects on follicular dynamics and peripheral insulin were determined. In a second experiment, 12 heifers were given a single injection of 10 ml saline or 320 mg BST in a sustained-release formulation to examine the temporal relationships between growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin and the number of follicles. The validation studies demonstrated that small follicles (< 5 mm in diameter) could be clearly detected by real-time ultrasound, and that 75% (9 of 12) of heifers showed three waves of dominant follicle development during the oestrous cycle, whereas the remainder had only two waves. The changes in the numbers of follicles of the three size categories (< 5 mm, small; 5-10 mm, medium-sized and > 10 mm, large) also displayed a wave pattern similar to that of the dominant follicle, with a marked reduction in the number of subordinate follicles as the dominant follicle grew and reached its maximum size. In Expt 1, BST treatment increased the number of small follicles and caused a rise in peripheral insulin concentrations (P < 0.01) throughout the treatment period.(ABSTRACT TRUNCATED AT 250 WORDS)