Ovulation In Heifers Research Articles

The revolution and future frontiers of reproductive management of dairy cattle

The 21-d pregnancy rate is determined by an interaction be­tween the AI service rate and pregnancies per AI (P/AI) and is a key performance indicator for the reproductive efficiency of dairy farms. Over the past 2 decades, the reproductive per­formance of lactating dairy cows increased. A greater under­standing of endocrinology and the physiology of lactating dairy cows generated fertility programs (the Presynch-Ovsynch and Double Ovsynch protocols for TAI) that increase the service rate and P/AI compared with detection of estrus. Previously, synchronization of ovulation in heifers was associated with poor reproductive performance compared with detection of estrus. Several modifications determined through randomized-controlled studies gave rise to the 5-d CIDR-Synch protocol that has similar and more P/AI when heifers are inseminated with conventional and sexed semen, respectively, compared with detection of estrus. A hierarchy of reproductive needs exists for dairy farms that require fulfillment before a new need can emerge. Dairy farms must have a high 21-d pregnancy rate and good heifer management before adopting other advanced re­productive technologies such as genomic selection, sexed and beef semen, and in vitro-produced embryos. Adopting these ad­vanced reproductive technologies benefits dairy farms, howev­er, challenges still exist that need further investigation through randomized-controlled experiments to maximize the benefits

Short Estrous Cycle Post-ovulation in Peri-pubertal Sahiwal and Jersey Crossbred Heifers

This investigation focuses on analysing the follicular dynamics exhibited during peri-pubertal period in Sahiwal and Jersey crossbred heifers. The aim of the study was to assess first ovulation in the heifers following puberty (N=20; 10 for each breed). Heifers were subjected to alternate day trans-rectal ultrasonography (TRUS) when the diameter of dominant follicle surpassed 9 mm diameter. Transrectal ultrasonography (TRUS) was performed to observe and assess first ovulation in heifers. The size of the first pre-ovulatory follicle in Sahiwal and Jersey Crossbred heifer in peri-pubertal stage was 10.52±0.13 and 10.15±0.51 mm, respectively and the corpus luteum attained its maximum size of 13.89 and 11.26 mm, was significantly different (p<0.01) at day 8.6±0.4 and 8.2±0.48 in Sahiwal and Jersey crossbred heifers, respectively. The regression of corpus luteum (CL) adjudged by the Colour Doppler initiated on 10.6±0.4 and 11.0±0.63 day for Sahiwal and Jersey crossbred heifers, respectively. Some other follicular dynamics parameters i.e. day of wave onset, number of follicles recruited, inter-wave duration along with maximum diameter of dominant follicle, day of maximum diameter, growth rate, length of growth and static phase, duration of static phase and onset of atresia was recorded, however, no significant difference (p>0.05) was recorded between breeds. On an interesting note, the next estrous cycle for heifers did not lead to ovulation despite having follicular size more than10 mm in both the breeds.
 Conclusion: In peroration, peri-pubertal Sahiwal and Jersey crossbred heifers had notably precocious luteal regression after first ovulation, without subsequent ovulation in next estrous cycle.

6 Immunological aspects of ovarian follicle ovulation and corpus luteum formation in cattle

Ovarian follicle ovulation and subsequent luteinization have been described as a controlled inflammatory event, comprising tissue damage and repair. To elaborate this further in cattle, the contribution of immune cells to dominant follicle luteinization, ovulation, and corpus luteum formation was investigated. Ovulation in beef heifers was synchronized using an 8-day progesterone-based synchronization program. Heifers were slaughtered at a local abattoir at 5 timepoints (T): (T1) 24h before ovulation (n=10); (T2) 2h before ovulation (n=9); (T3) 6h after ovulation (n=10); (T4) 24h after ovulation (n=10); (T5) 72h after ovulation (n=10), and ovarian tissue was collected and returned to the laboratory on ice. Follicular fluid, theca, granulosa, and corpus luteum (CL) tissues were recovered by dissection and processed for analysis. The concentrations of a panel of cytokines were measured using an antibody-conjugated magnetic bead immunoassay. The abundance of T-lymphocytes, mast cells, neutrophils, eosinophils, monocytes, macrophages, and dendritic cells was determined by immunohistochemistry. The mRNA relative abundance of candidate genes, including angiogenic growth factors, adhesion factors, chemokines and cytokines, was determined by quantitative real-time PCR analysis. The resulting datasets were analysed using the linear mixed model procedure of SAS and data are presented as least squares means; reported differences were deemed significant at P≤0.05. The cytokines IFNy, IP-10, IL-10, IL-36RA, MCP-1, MIP-1a, MIP-1b, and VEGF-A were detected in follicular fluid. The concentrations (pg mL−1) of IL-10 and VEGF-A were significantly higher in T1 follicular fluid samples compared with T2 (7.70 vs. 0.86 and 2193.33 vs. 293.93, respectively). Although dendritic cells were the most abundant cells in bovine ovulatory follicular and early corpus luteum tissue at all time points (P<0.05), their numbers peaked in ovulatory (T2) thecal tissue (261.5 cells/mm2). The greatest number of neutrophils was identified in thecal tissue at T1 (45/mm2); thereafter, their numbers declined to 1.1/mm2 in CL tissue by T5. Similarly, the numbers of T-lymphocytes, mast cells, monocytes, and macrophages declined in CL tissue at T4 and T5. Candidate gene mRNA expression profiles appeared to be time- and tissue-specific; for example, IFNA was highest in the preovulatory granulosa tissue (T1), IL8 was highest in peri-ovulatory thecal tissue (T2), VEGFA and MMP9 were highest in the early CL tissue (T4 and T5), MMP1, TIMP1, and VCAM1 expression was highest in theca, granulosa, and CL tissue collected on or after ovulation (T2, T4, T5), expression of the prostaglandin-related genes PTGES and PTGS2 was lowest in CL tissue, and that of PTGIS was highest. The current findings support the hypothesis that ovulation in heifers is characterised by an initial proinflammatory cascade followed by a dramatic switch to tissue repair, growth, and remodelling, all occurring within a 72-h period and commencing with the LH surge. Our results highlight the roles of neutrophils, dendritic cells, and macrophages as the key actors in this process.

Effect of number of 6-mm predeviation follicles and intraovarian patterns on right-side ovulation in heifers

The mechanisms underlying the greater frequency of ovulation from right ovary (RO) than left ovary (LO) were studied in 145 Bos taurus heifers. Diameter deviation during a follicular wave is indicated by continued diameter increase in the future preovulatory follicle (PF) and a decrease in diameter of future subordinate follicles. The PF (ovulation) was in the RO (63/105, 60%) more frequently (P < 0.04) than in the LO (40%) for ovulatory wave 2 of two-wave interovulatory interval (IOI) but not for wave 3 of three-wave IOI (RO, 45%; LO, 55%). The difference between waves 2 and 3 was associated with a greater (P < 0.01) number of 6-mm follicles during predeviation in the RO (2.3 ± 0.2 follicles) than LO (1.8 ± 0.1) for wave 2 but not for wave 3. Combined for ovulatory waves 2 and 3, the PF developed in the ovary with more 6-mm follicles during more (P < 0.0001) ovulatory waves (72%) than when the PF developed in the ovary with fewer follicles (11%). Ovulation from RO was more frequent (P < 0.02) when both PF and CL were in RO (46/72, 64%) than in LO (36%), but not when PF was alone in RO without the CL. Results supported the hypotheses that: (1) the number of 6-mm predeviation follicles developing during the ovulatory wave is greater for RO and (2) the number of predeviation follicles is greater for the ovary in which the preovulatory follicle subsequently develops.

Factors affecting side of ovulation in heifers and mares—A comparative study

Effect of side (left ovary, LO; right ovary, RO) and intraovarian presence of the regressing corpus luteum (CL) on the preovulatory follicle (PF) and ovulation were studied using ultrasonic- records of complete interovulatory intervals (IOI) for 500 IOI in heifers and 485 IOI in mares. Only IOI with a recording of side of a single PF and a single CL at each end of the IOI were used. In heifers, ovulation at the end of the IOI occurred more frequently (P < 0.0001) from RO (n = 285, 57%) than LO (n = 215, 43%). In mares, frequency of ovulation did not differ between RO (n = 250. 52%) and LO (n = 235, 48%). In heifers but not in mares, the number of predeviation follicles has been reported to be greater in RO than LO. In heifers, RO ovulation was more frequent when CL was in PF ovary (66%) than when CL was in opposite ovary (50%). There was no difference in side of ovulation (RO, 50%, LO, 50%). In mares, there were no significant main effects or interactions for frequency of ovulation involving side and intraovarian presence of the CL. On a species comparative basis, the present and reported results supported hypothesis 1 that a greater number of predeviation follicles in RO than in LO is associated with the predilection for RO ovulation. Results supported hypothesis 2 that ovulation in heifers is more frequent from RO than LO only when the preovulatory follicle and regressing CL are in the same ovary.

Synchronization of ovulation in cattle with an aromatase inhibitor–based protocol

A study was designed to determine the effect of stage of the estrous cycle on the proportion of animals that ovulated and the synchrony of ovulation of heifers treated with an aromatase inhibitor–based protocol. Forty-eight heifers were treated intramuscularly with 500 μg of cloprostenol (PGF) followed by 100 μg of GnRH 24 hours later to serve as control data for comparison of the ovulatory response to a subsequent aromatase inhibitor protocol. Daily ultrasound examinations were done to determine the incidence of and interval to ovulation. At the time of ovulation (Day 0), heifers were assigned randomly to five day-groups (n = 8-11/group) and given an intravaginal device containing 3 g of letrozole for 4 days starting on Day 0, 4, 8, 12, or 16. At the time of device removal, heifers were given PGF followed by GnRH 24 hours later. Ultrasound examinations were done daily from 2 days before device insertion to 9 days after the posttreatment ovulation. The preovulatory follicle diameter after letrozole treatment was larger in the Day 4 group compared to the Day 0 and 16 groups and intermediate in the Day 8 and 12 groups (P < 0.001). Compared to control data, the percentage of heifers that ovulated after letrozole treatment was greater (87.1% vs. 69.4%, respectively; P < 0.05) as was the synchrony of ovulation (residuals: 0.24 ± 0.07 vs. 0.68 ± 0.13; P < 0.01). The day on which letrozole treatment was initiated did not affect the proportion of heifers that ovulated or the interval to ovulation. Plasma estradiol concentrations at the time of removal of the letrozole device in the Day 0 and 4 groups was lower (P < 0.05) than in the corresponding controls. Estradiol concentrations in the Day 8 and 12 groups did not differ from already low concentrations in the respective controls. Corpus luteum diameter profiles and progesterone production were not affected by day-group although reduced luteal lifespan after letrozole treatment was observed and requires further investigation. In summary, a protocol involving a letrozole-impregnated intravaginal device for 4 days, PGF treatment at device removal, and GnRH 24 later resulted in a greater ovulation rate and greater synchrony of ovulation than in heifers not given letrozole. Results suggest that the protocol may be initiated effectively at random stages of the estrous cycle and may provide impetus for further studies to assess the efficacy of a letrozole-based synchronization protocol for fixed-time insemination.

Systemic effect of follicle-stimulating hormone and intraovarian effect of the corpus luteum on complete regression vs recovery of regressing wave-2 follicles in heifers

Each subordinate of the second follicular wave (wave 2) was monitored, and the outcome was classified as fully regressed (decreased in diameter to 2 mm) or recovered (decreased initially and then increased to become a growing follicle of the subsequent wave 1). The changing diameter of each follicle after emergence at 2 mm and plasma concentration of follicle-stimulating hormone were determined every 12 h from the day of ovulation (Day 0) to 4 d after the subsequent ovulation in heifers with 2 follicular waves per interovulatory interval (n = 10). The number and percentage of wave-2 subordinates that initially regressed and then recovered (7.2 ± 1.0 follicles; 33.2 ± 5.1%) were less (P < 0.0008) than the number and percentage that completely regressed (15.0 ± 1.7; 66.8 ± 5.1%). Follicles that later recovered initially reached maximal diameter on a later day (P < 0.0001) after emergence at 2 mm (4.3 ± 0.2 d) and at a larger (P < 0.0001) diameter (5.8 ± 0.2 mm) than follicles that completely regressed (3.2 ± 0.1 d; 4.7 ± 0.1 mm). The follicle-stimulating hormone surge that stimulated wave 2 began earlier and was more sustained in a subgroup with a high percentage of recovered follicles (61%) than in a subgroup with a low percentage (24%). Recovery began on Day −1.0 ± 0.1 when the follicles had regressed to 3.7 ± 0.1 mm. Diameter of subordinate follicles on Day −6 or before the expected days of luteolysis was greater (P < 0.05) when in the corpus luteum (CL) ovary than when in the non-CL ovary. During expected luteolysis, more follicles (P < 0.008) per ovary continued to regress when ipsilateral to the CL (9.2 ± 1.1 follicles) than when contralateral (5.8 ± 1.1), and more follicles (P < 0.02) recovered from regression when contralateral to the CL (5.0 ± 0.8) than when ipsilateral (2.2 ± 0.6). The hypothesis that the CL has a local effect on the development, regression, and recovery of the subordinate follicles of wave 2 was supported.

Bioactivity of ovulation inducing factor (or nerve growth factor) in bovine seminal plasma and its effects on ovarian function in cattle

To understand the role of ovulation-inducing factor (or nerve growth factor) (OIF [NGF]) in bovine seminal plasma, we (1) used an in vivo llama bioassay to test the hypothesis that bovine seminal plasma induces ovulation and CL development in llamas similar to that of llama seminal plasma when the dose of seminal plasma is adjusted to ovulation-inducing factor content (experiment 1) and (2) determined the effect of bovine seminal plasma on the interval to ovulation and luteal development in heifers (experiment 2). Within species, seminal plasma was pooled (n = 160 bulls, n = 4 llamas), and the volume of seminal plasma used for treatment was adjusted to a total dose of 250 μg of ovulation-inducing factor. In experiment 1, mature female llamas were assigned randomly to four groups and treated intramuscularly with either 10 mL of PBS (negative control, n = 5), 50-μg GnRH (positive control, n = 5), 6-mL of llama seminal plasma (n = 6), or 12 mL of bull seminal plasma (n = 6). Ovulation and CL development were monitored by transrectal ultrasonography. In experiment 2, beef heifers were given a luteolytic dose of prostaglandin followed by 25-mg porcine LH (pLH) 12 hours later to induce ovulation. Heifers were assigned randomly to three groups and given 12 mL bovine seminal plasma intramuscularly 12 hours after pLH treatment (n = 10), within 4 hours after ovulation (n = 9), or no treatment (control, n = 10). Ovulation was monitored by ultrasonography every 4 hours, and the CL development was monitored daily until the next ovulation. In experiment 1, ovulation was detected in 0/5, 4/5, 4/6, 4/6 llamas in the PBS, GnRH, llama seminal plasma, and bovine seminal plasma groups, respectively (P < 0.05). Luteal development was not different among groups. In experiment 2, the interval to ovulation was more synchronous (range: 4 vs. 22 hours; P < 0.0001) in heifers treated with seminal plasma before ovulation compared with the other groups. Luteal development was not different among groups; however, plasma progesterone concentrations tended to be greater in the postovulation treatment group compared with other groups. In summary, results confirmed the presence of bioactive ovulation-inducing factor in bull seminal plasma and supported the hypothesis that bovine and llama seminal plasma have similar ovulatory effects, using a llama bioassay. Treatment with bovine seminal plasma resulted in greater synchrony of ovulation in heifers pretreated with pLH. Plasma progesterone concentration tended to be higher in heifers given bovine seminal plasma within 4 hours after ovulation, suggesting that bovine ovulation-inducing factor is luteotrophic.

Minor FSH surge, minor follicular wave, and resurgence of preovulatory follicle several days before ovulation in heifers

Blood samples were collected and follicle diameters were determined daily beginning on Day 12 (Day 0 = ovulation) in 35 interovulatory intervals (IOIs) in heifers. A minor follicular wave with maximal diameter (6.0 ± 0.3 mm) on Day −4 was detected in six of seven IOIs that were scanned for follicles 4 mm or greater. The number of IOIs with a CV-identified minor FSH surge toward the end of the IOI was greater (P < 0.03) in two-wave IOIs (10/17) than in three-wave IOIs (4/18). The 17 two-wave IOIs were used for study of the temporal relationships among preovulatory follicle, FSH, LH, and estradiol. Daily growth rate of the preovulatory follicle was maximum on Days −11 to −7, minimum (P < 0.05) on Days −7 to −4, and increased (resurged, P < 0.05) on Days −4 to −3. A transient increase in FSH was maximum on mean Day −4, and the peak of a minor FSH surge occurred on Day −4.5 ± 0.2. Concentration of LH and estradiol increased between Days −5 and −4. Results demonstrated resurgence of the preovulatory follicle apparently for the first time in any species. Resurgence seemed more related temporally to the minor FSH surge than to the LH increase, but further study is needed. Results supported the novel hypotheses that a minor FSH surge near the end of the IOI is temporally associated with (1) the emergence of a minor follicular wave and (2) the resurgence in growth rate of the preovulatory follicle.

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.

Effect of purified llama ovulation-inducing factor (OIF) on ovarian function in cattle

Two experiments were designed to determine the effect of purified ovulation inducing factor (OIF) on ovarian function in cattle. In Experiment 1, prepubertal heifers (n = 11 per group) were treated on Day 5 (Day 0 = day of follicular wave emergence) of the follicular wave with an intramuscular dose of saline (1 mL), GnRH (100 μg), or purified OIF (1 mg/100 kg body weight). Ovulation occurred in 9/11 heifers treated with GnRH, and 1/11 heifers in each of the OIF- and saline-treated groups (P < 0.05). Compared to saline-treated controls, OIF treatment was associated with a smaller dominant follicle diameter (P < 0.01), a rise in plasma FSH concentration (P < 0.1), and earlier emergence of the next follicular wave (P < 0.05). In Experiment 2, sexually mature heifers were given either GnRH or purified OIF on Days 3, 6 or 9 of the first follicular wave (i.e., early growing, early static, or late static phase of the dominant follicle; n = 5 per group per day), or were untreated (n = 10). In heifers treated with OIF on Day 6, the dominant follicle diameter profile tended to be smaller than in controls, and was associated with a rise (P < 0.05) in plasma FSH concentrations. A similar rise in FSH was detected after OIF treatment on Day 9. Compared to untreated controls, treatment with OIF and GnRH was associated with a larger CL diameter (Days 3 and 6 groups; P < 0.05) and a greater concentration of plasma progesterone (Days 6 and 9 groups; P < 0.05). Treatment with purified OIF did not induce ovulation in heifers, but hastened new follicular wave emergence in prepubertal heifers, influenced follicular dynamics in a phase-specific manner in mature heifers, and was luteotrophic.

Inhibition of prostaglandin biosynthesis during postluteolysis and effects on CL regression, prolactin, and ovulation in heifers

The beginning of postluteolysis (progesterone, <1 ng mL−1) in heifers was targeted by using 8 h after ultrasonic detection of a 25% decrease in CL area (cm2) and was designated Hour 0. Flunixin meglumine (FM; n = 10) to inhibit PGF2α secretion or vehicle (n = 9) were given intramuscularly at Hours 0, 4, 8, 16, 24, 32, and 40. The dose of FM was 2.5 mg/kg at each treatment. Blood sampling and measurement of the CL and dominant follicle were done every 8 h beginning 14 days postovulation in each group. Blood samples for detection of pulses of PRL and pulses of a metabolite of PGF2α (PGFM) were obtained every hour for 24 h beginning at Hour 0. Pulse concentrations of both PGFM and PRL were lower in the FM group than in the vehicle group. Concentration of PRL was greatest at the peak of a PGFM pulse. Neither CL area (cm2) nor progesterone concentration differed between groups during Hours 0 to 48 (postluteolysis). Ovulation occurred in nine of nine heifers in the vehicle group and in three of 10 heifers in the FM group. The anovulatory follicles in the FM group grew to 36.2 ± 2.9 mm, and the wall became thickened from apparent luteinization. The hypothesis that PGF2α was involved in the continued P4 decrease and structural CL regression during postluteolysis was not supported. However, the hypotheses that pulses of PGFM and PRL were temporally related and that systemic FM treatment induced an anovulatory follicle were supported.

219 FOLLICLE AND HORMONE DYNAMICS IN SINGLE- v. DOUBLE-OVULATING HEIFERS

The present experiment used the Day 4 ablation model for increasing the incidence of double ovulations in heifers. The objective was to compare follicle growth and plasma hormone concentrations associated with single v. double ovulations. Follicles ≥5 mm were ablated at 4 days post-ovulation to induce a prominent FSH surge and a new follicular wave, and 2 injections of PGF2 (12 h apart) were given 2 days later (Day 6) to favor ovulation. Beginning on Day 5, the 3 largest follicles of the induced wave were scanned twice a day until 36 h after the next ovulation. Blood samples were taken at 6-h intervals starting when the largest follicle reached ≥8.0 mm (expected deviation at 8.5 mm; Ginther et al. 1996) and continued until 36 h after the next ovulation. Concentrations of LH and FSH were measured by validated RIA for cattle (LH measured by Ginther et al. 1999; FSH measured by Adams et al. 1992) and concentrations of oestradiol measured by a commercially available RIA kit (Siddiqui et al. 2009). From a total of 31 heifers, 16 (52%) or 15 (48%) developed a single or more than 1 dominant (≥ 10 mm) follicle in the follicular wave after ablation, respectively. For heifers with 2 dominant follicles, the second-largest follicle ovulated in 9 (60%) heifers and the overall double ovulation rate was 29% (9/31). Follicle diameters and plasma hormone concentrations were compared between single ovulators (n = 12) and double ovulators (n = 8). Diameter of the preovulatory follicles did not increase between the LH peak and ovulation in either the single or double ovulations. In double ovulators, the interval from follicle deviation to the peak of the preovulatory LH surge was shorter (1.9 ± 0.2 days v. 2.5 ± 0.2 days; P &lt; 0.02) and the diameter of the largest preovulatory follicle was smaller (12.2 ± 0.5 mm v. 13.3 ± 0.3 mm; P &lt; 0.02) than in single ovulators, respectively. The LH concentrations of the preovulatory surge did not differ between single and double ovulators for 24 h on each side of the peak (main effect of hour only; P &lt; 0.0001). When data were normalized to the LH peak, the peak of the preovulatory FSH and estradiol surges occurred in synchrony with the peak of LH surge for both groups. A group effect (P &lt; 0.0001) for FSH resulted from a lower concentration averaged over hours in double ovulators. Estradiol showed a group by hour interaction (P &lt; 0.008), reflecting greater concentrations in the double ovulators before and at peak. In conclusion, an increased Supported by the Eutheria Foundation, Cross Plains, WI, USA. Submission supported by FAPEMIG.

Effect of Escherichia coli infection of the bovine uterus from the whole animal to the cell

Following parturition, contamination of the uterine lumen by bacteria is ubiquitous, and uterine health is impaired in cattle because infection persists in 10% to 15% of animals as endometritis. Endometritis causes infertility for the duration of infection, and subfertility persists even after apparent successful resolution of the disease. Escherichia coli is the pathogenic bacterium most frequently isolated from the post partum uterus, and is associated with increased concentrations of peripheral plasma acute phase proteins and fetid vaginal mucus. The presence of E. coli is also associated with slower growth of the first post partum dominant follicle and perturbed oestradiol secretion. Furthermore, in animals that ovulate the first dominant follicle, the corpus luteum is smaller and secretes less progesterone. The endotoxin lipopolysaccharide (LPS), which is released from E.coli, can pass from the uterine lumen to the peripheral circulation and LPS concentrations are increased in cows with uterine infection. Infusion of E. coli LPS into the uterine lumen suppresses the pre-ovulatory luteinising hormone surge and disrupts ovulation in heifers. In vitro, endometrial explants produce prostaglandins in response to LPS. Addition of LPS or E. coli to stromal or epithelial cells increases cyclooxygenase-2 mRNA expression, and stimulates the production of prostaglandin E2 and prostaglandin F2α. Furthermore, uterine and ovarian cells express mRNA of the molecules required for recognition of LPS, Toll-like receptor-4 and CD14. In summary, E. coli is a common cause of infertility involving the perturbation of the hypothalamus, pituitary and ovary in dairy cows.

Effect of Monopropylene Glycol on Luteinizing Hormone, Metabolites, and Postpartum Anovulatory Intervals in Primiparous Dairy Cows

This study examined the effect of monopropylene glycol (MPG) supplementation on LH secretion, postpartum interval to first ovulation, and milk production in heifers calving with poor body condition score (BCS). Forty-seven heifers were allocated to 3 treatments: 1) heifers with high BCS (BCH; n=13) that calved at a BCS of 3.4 (BCS scale of 1 to 5); 2) heifers with low BCS (BCL; n=17) that calved at a BCS of 2.8; and 3) heifers with low BCS that calved at a BCS of 2.8 and were assigned to receive MPG supplementation (BCL + MPG; n=17) and grazed pasture ad libitum. Monopropylene glycol was drenched (250mL) twice daily for 16 wk after calving. Patterns of change in plasma LH were measured at 2 and 5 wk after calving. Pulsatile release of LH at 2 and 5 wk was greater in BCL + MPG and BCH cows compared with the BCL control cows. The BCL + MPG cows had lower NEFA concentrations than did the BCL cows during wk 1 to 6 after calving. At 12 wk postpartum, the proportion of cows cycling was 77, 82, and 28% for the BCH, BCL + MPG, and BCL treatments, respectively. Mean milk fat yield was greater for the BCH treatment during the first 12 wk postpartum compared with the BCL + MPG or BCL treatments, which did not differ from each other. Results of this study indicate that MPG supplementation reduced the interval from calving to first ovulation in heifers having poor body condition at calving.

164 EFFECT OF OVULATION-INDUCING FACTOR (OIF) ON OVARIAN FUNCTION IN CATTLE

Systemic administration of ovulation-inducing factor (OIF), discovered recently in seminal plasma of llamas, alpacas (induced ovulators), and cattle (spontaneous ovulators), stimulated ovulation in &gt;90% of female llamas and alpacas. The objective of the present study was to test the hypothesis that purified OIF from llama seminal plasma would induce ovulation in cattle. Peripubertal heifers, weighing 323 � 27 kg, were used to minimize the confounding effect of spontaneous ovulation. Heifers (n = 11/group) were treated intramuscularly with 1.0 mg/100 kg of purified OIF, 100 µg of GnRH (positive control), or 2.5 mL of phosphate-buffered saline (negative control). Ovarian dynamics were monitored daily by transrectal ultrasonography for 10 days post-treatment. Blood samples were collected at 0.5- to 1-h intervals for 8 h, beginning at the time of treatment. Ovulation occurred in 9/11 (82%) of GnRH-treated heifers and in 1/11 (9%) heifers in each of the OIF- and saline-treated groups (P &lt; 0.05). A surge in plasma LH concentration was detected within 30 min of treatment in the GnRH group (2.2 � 0.1 ng mL–1; P &lt; 0.05), but remained at the basal level in the OIF- and saline-treated groups (0.3 � 0.1 and 0.2 � 0.1 ng mL–1, respectively). The onset of regression of the dominant follicle present at the time of treatment was earlier (P &lt; 0.05) in OIF- v. saline-treated heifers (3.1 � 0.6 days v. 6.0 � 0.7 days). The interval from treatment to follicular wave emergence was shorter (P &lt; 0.05) in GnRH- and OIF-treated heifers than in those treated with saline (1.1 � 0.4 days, 1.5 � 0.3 days, and 3.1 � 0.3 days, respectively). A similar pattern was observed for emergence of the second follicular wave (5.1 � 0.7 days, 4.6 � 0.5 days, and 6.6 � 0.4 days, respectively). Purified OIF did not induce ovulation in heifers but hastened both the regression of the extant dominant follicle and follicular wave emergence. Results provide a rationale for the hypothesis that OIF from seminal plasma is involved in controlling follicular wave dynamics in spontaneously ovulating species (e.g., Bos taurus) through a suppressive effect on the dominant follicle. The mechanism of action on ovarian follicular wave dynamics, as well as species specificity, remains to be elucidated.

Antral follicle growth and endocrine changes in prepubertal cattle, sheep and goats

In the growing heifer calve, there is an early post-natal, gonadotrophin driven increase in ovarian antral follicle growth. The endocrine regulation of and reason for this initial stimulation of ovarian follicular development are not fully understood. This initial endocrine activity appears to be later held in check by negative feedback suppression mechanisms until the heifer is of a sufficient body size to initiate oestrous cycles and to reproduce. There is increasing evidence from recent ultrasonographic studies, performed in the same groups of prepubertal heifer calves, that the development of ovarian antral follicles and tubular genitalia occur in parallel. There appear to be two distinct periods of enhanced development of the reproductive organs, from 2 to 14 weeks of age and again from 34 to 60 weeks of age, or just prior to puberty. First ovulation in heifers is preceded by a gradual increase in pulsed LH secretion, which results in enhanced antral follicle development and oestrogen production. It was demonstrated that prepubertal heifers produced recurrent antral follicular waves; maximum sizes and life span of the dominant follicles of waves, as well as periodicity and FSH dependency of wave emergence were similar to those in adult cattle. In does, no Graafian follicles are seen at birth and total follicle numbers increase to 2 months of age, and then decline to 5 months of age. In ewe lambs, studies using transrectal ovarian ultrasonography showed that antral follicle recruitment and growth increased after the first 2 months of age and just before puberty. This bi-phasic pattern of changes in ovarian follicle recruitment and growth is strikingly similar to that in heifer calves, but it contrasts with earlier post-mortem examinations of ovaries in ewe lambs. Unlike in cattle and adult ewes, the rhythmic pattern of follicular wave emergence was not established in pre- and peripubertal ewe lambs. The early increase in antral follicle numbers and size in ewe lambs may be, at least in part, due to changes in FSH release and potency, and enhanced follicle production prior to first ovulation is probably caused by an increase in the frequency of LH pulses.

Effect of oestradiol benzoate given after prostaglandin at two stages of follicle wave development on oestrus synchronisation, the LH surge and ovulation in heifers

Oestrus synchronization following prostaglandin-induced luteolysis is variable and dependent on follicle wave status in cattle. Oestradiol benzoate (ODB) has been used following prostaglandin to reduce the interval to oestrus and ovulation, but the effect of follicle wave status at the time of ODB administration is not clear. The aim of this study was to characterize the endocrine and follicular responses following ODB after luteolysis at different stages of the follicle wave. Prostaglandin was administered at either emergence or dominance of the second follicle wave. Twenty-four hours later animals received either 0.5 mg ODB in oil or a control oil injection. Follicular development was monitored daily by ultrasonography, oestrous behavior was determined and blood samples were collected. In animals treated with ODB at emergence, there was a reduction ( P<0.05) in the maximum diameter of the ovulatory follicle (11.7±1.2 mm versus 13.1±0.1 mm) and in the interval from prostaglandin to oestrus (52.0±2.3 h versus 88.0±9.6 h), to the LH surge (53.3±3.5 h versus 89.1±6.5 h) and to ovulation (96±0.0 h versus 129.6±9.6 h), compared with controls. In animals treated with ODB at dominance, there was a reduction ( P<0.05) in the interval from prostaglandin to the LH surge (54.0±3.1 h versus 70.9±4.8 h), but not in the interval from prostaglandin to oestrus (53.3±2.7 h versus 65.7±4.5 h; P=0.11), to ovulation (96.0±0.0 h versus 110.4±4.8 h; P=0.12) or the maximum diameter of the ovulatory follicle (12.7±0.3 mm versus 13.6±0.4 mm; P=0.12), compared with controls. Treatment did not affect ( P>0.05) the length of the subsequent oestrous cycle or corpus luteum size. In conclusion, the use of ODB advanced, but did not alter the temporal relationships among oestrus, the LH surge and ovulation, regardless of stage of follicle development at treatment.

Changes in concentrations of plasma immunoreactive follicle-stimulating hormone, luteinizing hormone, estradiol-17β, testosterone, progesterone, and inhibin in heifers from birth to puberty☆

This study was designed to clarify the characteristics of changes in plasma concentrations of reproductive hormones in heifers from birth to puberty. Weekly or daily hormonal changes were observed in 39 heifers. Daily changes in the concentration of follicle-stimulating hormone (FSH) demonstrated a consistent cycle of hormone changes over a 7- to 8-day period in heifers from approximately 10 days to 9 months old. Weekly changes in reproductive hormones showed that there were three brief periods in heifers between birth and puberty in which dramatic changes occur. The first period was the first week after birth, during which a reciprocal relationship between steroid hormones and gonadotropins was observed. At birth, the concentrations of steroid hormones were higher than those at any other age. These hormone levels rapidly decreased within the first week after birth. Gonadotropin levels, however, increased from birth to 1 week of age. The second period of major change was at approximately 4 weeks of age when there was an increase in the concentrations of luteinizing hormone (LH), estradiol-17β, testosterone, and immunoreactive inhibin. The third period was the last 5 weeks before the first ovulation, when there was an increase in the concentrations of estradiol-17β followed by an increase in (LH). These results suggest that regular hormone changes start from 10 days after birth and that the periods from birth to 4 weeks of age and the last 5 weeks before the first ovulation in heifers are important to the development of reproductive functions before puberty.

Transvaginal, ultrasound-guided biopsy of the corpus luteum in cattle

An ultrasound-guided transvaginal technique for corpus luteum biopsy was developed and tested in cattle. The biopsy needle set consisted of an inner needle (o.d. 1 mm) with a 20-mm long specimen notch, an outer cannula (o.d. 1.2 mm) with a cutting edge, and an automated spring-loaded handle with trigger. The biopsy needle set was inserted into the channel guide of the handle of a convex-array transvaginal ultrasound probe. The transducer was positioned in the vaginal fornix, and the ovary was manipulated transrectally against the vaginal wall and transducer face. During monitoring on the ultrasound screen, the inner needle was pushed through the vaginal wall into the corpus luteum, and the cutting cannula was fired, cutting and trapping luteal tissue in the specimen notch. Three luteal biopsies at each of Hours 0 and 4 were taken 10 d after ovulation in heifers; 6 other heifers served as controls. A biopsy core was obtained in 36 of 39 attempts (92%). The tissue specimens seemed normal based on gross evaluation. The effect of biopsy on luteal function was assessed by daily ultrasound monitoring of luteal area, by assay of progesterone concentrations in blood samples obtained daily, and by the length of the interval from biopsy to ovulation. No significant differences were found for postbiopsy function for any of the 3 end points. The results indicated repeated transvaginal, ultrasound-guided biopsy of the corpus luteum in cattle is a practical procedure and may be useful for experimental and diagnostic purposes,