Ovulation Interval Research Articles

122 TIMED ARTIFICIAL INSEMINATION IN WOOD BISON USING FROZEN-THAWED SEMEN

Recent progress with methods to control ovulation and semen cryopreservation in Wood Bison was the impetus to test the feasibility of timed AI to facilitate reclamation of this threatened species. A 2 × 2 design was used to compare the efficacy of 2 ovulation synchronization techniques and 2 semen cryopreservation protocols. Female Wood Bison were assigned randomly to 2 groups (n = 24/group) in which ovarian synchronization was induced by ultrasound-guided ablation of follicles >5 mm or intramuscular treatment with 2.5 mg of estradiol 17B + 50 mg of progesterone (E+P) in canola oil. A progesterone-releasing intravaginal device (PRID) was placed at the time of follicle ablation (for 5 days) or E+P treatment (for 8 days) in the respective groups. A luteolytic dose of prostaglandin was given at the time of PRID removal, and 2500 IU of hCG was given IM 3 days later. Bison were inseminated 24 and 36 h after hCG treatment using frozen-thawed semen. The semen was collected by electro-ejaculation from 4 Wood Bison bulls, pooled, and divided into aliquots diluted in either egg-yolk extender (EY) or cholesterol-loaded cyclodextrin extender (CLC). Half the bison in each synchronization group were inseminated with either EY- or CLC-extended semen. Bison were examined by ultrasonography every 12 h beginning on the day of hCG treatment for 3 days or until ovulation was detected, whichever occurred first. Pregnancy diagnosis was made by ultrasonography 34–36 days after insemination. Two bison were excluded during the experiment because of handling difficulty; therefore, the total number of bison used was 46. Ovulation rate and interval to ovulation were compared between synchronization groups by chi-square and t-test, respectively. Pregnancy rates were compared among groups by 2-way ANOVA after transforming data to arcsin. The ovulation rate was not different between synchronization groups [combined mean, 37/46 (80%)], nor was the degree of synchrony, as assessed by the residuals (variation from the mean) in the respective groups. However, the diameter (mean ± standard error of the mean) of the dominant follicle at the time of hCG treatment was smaller in the follicle ablation group than in the E+P group (10.5 ± 0.6 v. 13.9 ± 0.6; P < 0.04), and the interval from hCG treatment to ovulation tended to be longer (35.3 ± 1.6 v. 31.8 ± 1.3 h; P ≤ 0.10). Pregnancy rate was not affected by synchronization procedure, but pregnancy was detected only in the EY-inseminated group (9/23 v. 0/23; P < 0.01). Despite that post-thaw sperm motility was similar for EY and CLC semen (41.7 ± 2.9 and 44.6 ± 3.3%; respectively), CLC-treated semen failed to impregnate bison in vivo. We concluded that synchronization and timed insemination with frozen-thawed semen is feasible in Wood Bison. Of the 23 bison inseminated with EY-extended semen, 21 ovulated (91%), and of those that ovulated 9 became pregnant (43%). Both synchronization schemes were effective, but the ablation protocol may be improved by an additional day between ablation and hCG treatment. We thank Vetoquinol Canada and Merck Animal Health for providing hormone treatments.

LH peak and ovulation after two different estrus synchronization treatments in buffalo cows in the daylight-lengthening period

The aim of this study was to determine the timing of ovulation in relation to the LH peak after synchronization using PRID or Ovsynch protocols, to assess the effects of the period of treatment on these parameters and to provide information concerning how to use the two main protocols for fixed-time artificial insemination in buffalo. Forty-eight lactating Italian Mediterranean buffalo cows were used. The buffaloes were treated in various periods as follows: February to March (n = 12 PRID, n = 12 Ovsynch), end of the breeding season, May to June (n = 12 PRID, n = 12 Ovsynch), beginning of low-breeding season according to Italian environmental conditions. To determine the LH, blood samples were taken at 4-hour intervals, starting 24 hours from PRID removal (PRID group) or 12 hours from (PGF2α) injection (Ovsynch group) up to 108 hours. The ovaries were monitored by transrectal ultrasonography to verify ovulation. The LH–ovulation interval was similar in both groups (30.10 ± 1.05 and 32.77 ± 1.15 hours, respectively, in PRID and Ovsynch group). In the PRID group, the timing of ovulation in relation to device removal was 76.83 ± 3.65 hours with a high level of variability among the animals. In the Ovsynch group, we observed a better synchronization of LH peaks and ovulations, and the timing of ovulation in relation to the last GnRH injection was 35.67 ± 1.15 hours. The percentage of animals reaching the LH peak and ovulation was lower (P ≤ 0.05) in May to June (respectively 75.0% and 54.1%) compared to February to March (respectively 95.8% and 83.3%), indicating a reduction of hypothalamus–pituitary responsiveness to the synchronization treatments in the daylight-lengthening period.

165 EFFECT OF INJECTION OF SEMINAL PLASMA ON OVULATION RATE, CORPUS LUTEUM DEVELOPMENT, AND SENSITIVITY TO PROSTAGLANDIN IN ALPACAS (VICUGNA PACOS)

The seminal plasma (SP) of camelids contains a protein identified as β Nerve Growth Factor with capacity of induced ovulation and develop a corpus luteum. A study was designed to evaluate the effect of application of SP on the interval of time from injection of stimulus to the ovulation and corpus luteum (CL) size (Experiment 1, n = 24) and on the sensitivity of CL to the injection of prostaglandin (196 µg of tiaprost) (PG) at different periods from ovulation (Experiment 2, n = 86). Exp. 1: Adult female alpacas with presence of a follicle ≥7 mm were assigned to the application of 1 mL of SP via IM (T: n = 12) or application of 50 µg of acetate of busereline IM (T2: n = 12). Exp. 2: Alpacas with presence of a follicle ≥7 mm were induced to ovulation with 50 µg of acetate of busereline or 1 mL IM of SP. Animals were evaluated by ultrasound to confirm the ovulation and were assigned to the following treatment: T1 (n = 8): SP + PG Day 4; T2 (n = 8): buserelin acetate + PG Day 4; T3 (n = 8): SP + PG Day 5; T4 (n = 8): buserelin acetate + PG Day 5; T5 (n = 8): SP + PG Day 6; T6 (n = 8): buserelin acetate + PG Day 6; T7 (n = 8): SP + PG Day 7; T8 (n = 8): buserelin acetate + PG Day 7; T9 (n = 8): SP + PG Day 8; T10 (n = 8): buserelin acetate + PG Day 8 and T11 (n = 6) (Control): Application of 1 mL of saline solution. The animals were evaluated by ultrasound with an Aloka SSD500 (Aloka, Tokyo, Japan) and 7.5-MHz linear transducer each 2 h (Exp. 1) and each 12 h (Exp. 2) after of application of PG. In Exp. 1, the ovulation rate was 95.7% to T1 and T2 and an interval of time between injection of stimulus and ovulation was 27.4 ± 2.5 h and 26.8 ± 1.8 to T1 and T2, respectively. In Exp. 2, luteolysis was 0.0%, 0.0%, 25.0%, 0.0%, 100.0%, 100.0%, 100.0%, 100.0%, 100.0%, 100.0%, and 0.0% for the treatments T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, and T11 respectively. The results suggest that no differences exist between in the ovulation rate and interval to the ovulation between the application of buserelin acetate or SP and that the CL was sensible at Day 5 to the prostaglandin respect SP and with similar response to the sensibility of CL from Day 6 to Day 8.

10 TIMED ARTIFICIAL INSEMINATION PROTOCOLS TO SYNCHRONIZATION OF OVULATION IN BOS TAURUS TAURUS SUCKLING BEEF COWS

The aim of this study was to compare 3 methods for synchronization of ovulation in anestrous beef cows. The hypothesis of this study was to determine whether low doses of hCG has superior efficacy to cypionate to induce ovulation in anestrous cows and provide higher pregnancy rate in oestrus-synchronization programs. Synchronization of ovulation and conception rate to timed AI (TAI) were evaluated in anestrus Bos taurus taurus suckling beef cows 45 ± 15 days postpartum and with body condition score of 2.9 (1 to 5) maintained in a native pastured system in the south of Brazil. Females were evaluated with ultrasound on the Day 0 (D0) of the protocol (Day 0), day 8 (D8), immediately before TAI (D10), and 7 days after TAI (Day 17). All cows were synchronized with an intravaginal progesterone-releasing device (IPRD; 0.75 g of progesterone, Prociclar®, Hertape Calier Animal Health, Juatuba, Brazil) and 2 mg IM of oestradiol benzoate (EB; Benzoato HC®) on D0. On Day 8, the IPRD was removed and 150 μg of D (+) cloprostenol (Veteglan Luteolytic®), and 25 IU IM FSH/LH (Pluset®) were administered. Females of the EC (n = 84) group received 1 mg IM of oestradiol cypionate (EC; Cipionato HC®). Females on D8 of the hCG (n = 81) group received 500 IU IM of hCG (Vetecor®, Hertape Calier) at the time of TAI. The females of the EC + hCG group (n = 83) received both treatments. All cows were submitted to TAI 54 h after withdrawal of IPRD. A part of the cows (n = 102) had the ovulation evaluated every 12 h from the withdrawal of IPRD [EC (n = 34), hCG (n = 34), and hCG + EC (n = 33)]. Statistical analysis was performed using SAS PROC GLIMMIX. The dominant follicle diameter (FD) on Day 8 (8.7 ± 0.2, 8.8 ± 0.2, 8.6 ± 0.2) did not differ between treatments EC, EC + hCG, or hCG (P = 0.79). However, the FD on D10 was higher (P = 0.001) for cows treated with hCG (12.9 ± 0.3) compared with cows from the EC (11.3 ± 0.2) or EC + hCG group (11.8 ± 0.2). The interval (h) between the withdrawal of IPRD and ovulation was lower (P = 0.01) for the hCG group, (71.2 ± 1.7) compared with the groups treated with EC or EC + hCG (76.6 ± 2.18 and 74.2 ± 1.65), respectively. The ovulation rate did not differ (P = 0.61) among the EC (85.2%, 29/34), hCG (91.1%, 31/34), or EC + hCG groups (90.9%, 30/33). Corpus luteum diameter (mm) was higher (P = 0.04) on D17 for the hCG-treated group (21.4 ± 0.3) compared with others treatments (EC = 19.1 ± 0.8 or EC + hCG = 20.4 ± 0.8). However, the plasma progesterone levels on D17 were EC = 2.0 ± 0.1, hCG = 2.4 ± 0.1, and EC + hCG = 2.3 ± 0.1 ng mL–1 (P = 0.19), and the conception rate on the 28th day after TAI (EC = 43.0%; hCG = 47.0%, and EC + hCG = 48.8%; P = 0.76) was also similar. The hCG determined smallest ovulation interval, but similar rates of pregnancy were observed with both treatments.

Effects of varying doses of β-nerve growth factor on the timing of ovulation, plasma progesterone concentration and corpus luteum size in female alpacas (Vicugna pacos).

Ovulation in camelids is induced by the seminal plasma protein ovulation-inducing factor (OIF), recently identified as β-nerve growth factor (β-NGF). The present study measured the total protein concentration in alpaca seminal plasma using a bicinchoninic acid (BCA) protein quantification assay and found it to be 22.2±2.0mgmL(-1). To measure the effects of varying doses of β-NGF on the incidence and timing of ovulation, corpus luteum (CL) size and plasma progesterone concentration, 24 female alpacas were synchronised and treated with either: (1) 1mL 0.9% saline (n=5); (2) 4µg buserelin (n=5); (3) 1mg β-NGF protein (n=5); (4) 0.1mg β-NGF (n=5); or (5) 0.01mg β-NGF (n=4). Females were examined by transrectal ultrasonography at 1-2-h intervals between 20 and 45h after treatment or until ovulation occurred, as well as on Day 8 to observe the size of the CL, at which time blood was collected to measure plasma progesterone concentrations. Ovulation was detected in 0/5, 5/5, 5/5, 3/5 and 0/4 female alpacas treated with saline, buserelin, 1, 0.1 and 0.01mg β-NGF, respectively. Mean ovulation interval (P=0.76), CL diameter (P=0.96) and plasma progesterone concentration (P=0.96) did not differ between treatments. Mean ovulation interval overall was 26.2±1.0h. In conclusion, buserelin and 1mg β-NGF are equally effective at inducing ovulation in female alpacas, but at doses ≤0.1mg, β-NGF is not a reliable method for the induction of ovulation.

Effect of using frozen-thawed boar sperm differing in post-thaw motility in the first and second inseminations on pregnancy establishment, litter size, and fetal paternity in relation to time of ovulation1

Frozen-thawed boar sperm (FTS) has reduced motility and viability compared to cooled semen. Motility of FTS is related to in vitro and in vivo fertility, but this effect has not been determined in relation to the timing of ovulation. To test the effect of variable FTS motility in a multiple-AI system, ejaculates from 38 boars were collected and frozen in 0.5-mL straws. Upon thawing, samples were classified (mean ± SEM) by motility as poor (P, 20.2% ± 1.1%), moderate (M, 31.3% ± 0.9%), or good (G, 43.5% ± 0.8%). In replicates, mature gilts were synchronized and checked for estrus at 12-h intervals and assigned (n = 207) to receive 4.0 billion total sperm in each AI at 24 and 36 h after onset of estrus using the treatments: 1) P and M (P-M), 2) M and P (M-P), 3) G and M (G-M), and 4) M and G (M-G). For each treatment combination, a set of 3 boars was randomly selected within motility class for their allelic distinction with M sperm from a single boar represented across all treatments and sires used in both first and second inseminations. The insemination to ovulation interval (IOI) was determined using ultrasound every 12 h. Reproductive tracts were collected at approximately d 32 after AI. Treatment did not interact with IOI (P > 0.10) and did not affect (P > 0.10) pregnancy rate (57%, 67%, 71%, 76% ± 7.2%, pooled SEM) or total number of fetuses (9.2, 9.1, 9.5, 10.0 ± 0.8) for P-M, M-P, G-M, and M-G treatments, respectively. Treatment did affect (P < 0.05) the number of fetuses sired from the first AI (3.1, 7.2, 6.4, 6.3 ± 1.2) and second AI (5.7, 2.6, 3.0, 3.6 ± 0.9) for the P-M, M-P, G-M, and M-G treatments, respectively. The IOI also influenced (P < 0.05) the proportion of offspring sired by the second AI (30.0%, 57.7%, 51.3%, 18.3% ± 6.5%), as well as the number of fetuses sired by each AI. These results indicate FTS motility had no effect on pregnancy rate or litter size but did affect the number of fetuses sired from the first and second inseminations. The first AI appears to sire most of the litter except when P sperm was used. Number of fetuses sired was reduced when P sperm was used in either insemination compared to M, although no difference was evident between M and G. Fetal paternity appears to be a more sensitive marker for identifying the effects of sperm quality and IOI in a multiple-AI system with use of FTS. These results suggest that use of semen of various qualities can be used in combinations to aid in pregnancy establishment and contribute to litter size.

Postpartum reproductive activities and gestation length in Martina Franca jennies, an endangered Italian donkey breed

The donkey reproductive physiology is still partially known despite the increasing risk of extinction involving several breeds. The present study was designed to describe the postpartum (PP) reproductive performance of an Italian endangered breed: the Martina Franca donkey. To this aim, 52 jennies were monitored to define the foal-heat (FH) and the first and second PP estrus episodes (1st PPe and 2nd PPe). The data indicate that jennies spontaneously recovered reproduction in approximately 10 days after delivery. Then heats occur with a regular interval of approximately 23 days. Estrus length was 1 week in FH and the 2nd PPe and significantly shorter in the 1st PPe. Estrus–ovulation, and delivery–ovulation interval and follicle growth were similar in all animals tested. Pregnancy rate (PR) was lower when natural mating occurred during the FH and 2nd PPe (approximately 60%) than during the 1st PPe (approximately 70%; P < 0.01). In addition, the higher PR (>80%; P < 0.01) was recorded in jennies when the FH occurred after the first week PP and it dropped (<50%) in early FH animals. The PR was also affected by the season and by age: it significantly declined during the autumn–winter season and in subjects older than the sixth year of age. For the first time, the reproductive performance of PP donkeys were defined on a large number of Martina Franca jennies thus offering useful information to improve farm management with an immediate benefit to increase livestock production. This aspect of management improvement might be particularly important if applied to an endangered breed such as Martina Franca donkeys.

Cervical mucus characteristics and periestrual hormone concentration in relation to ovulation time in Zebu (Sahiwal) cattle

The present study was conducted to determine the association among cervical mucus characteristics, periestrual progesterone (P4) and luteinizing hormone (LH) concentrations and ovulation time in Zebu cattle. In experiment 1 the relationship between cervical mucus characteristics and ovulation time was determined. Cervical mucus was collected from Sahiwal cows (n=60) before artificial insemination from mid-cervix and rheological and chemical properties were studied. Ovulation time was determined by ultrasound examination at 2h intervals starting from the onset of estrus to ovulation. Cervical mucus was copious and thin in 70.2 and 63.2 percent of estrus periods, respectively. Cervical mucus from 57.9 percent of the estruses had a typical arborization pattern. The Means±SEM of pH, electrical conductivity and spinnbarkeit value of the mucus were 7.59±0.06, 15.21±0.15mS/cm and 11.06±1.06cm, respectively. Estrus to ovulation duration was significantly greater (P<0.05) in cows that had 8–16cm spinnbarkeit value of cervical mucus than cows with higher or lower values. In experiment 2 the relationship among peripheral P4, LH concentrations and ovulation time was determined. For this purpose blood samples were collected from 20 Sahiwal cows (10 natural estruses and 10 induced estruses) at 2h intervals from the onset of estrus until ovulation. Peripheral P4 and LH concentrations were measured using bovine-specific ELISA kits. The duration of estrus to LH-peak and LH-peak to ovulation was 2.2±1.62h and 29.45±1.73h in natural estrus and 3.3±0.67h and 32.75±3.62h in induced estrus, respectively. The peak LH value did not vary significantly in synchronised (15.26±2.8ng/mL) and natural estrus (12.67±1.96ng/mL). Plasma P4 concentration on the day of estrus was significantly greater (P<0.05) in the synchronised estruses (1.23±0.23ng/mL) compared to the natural estruses (0.65±0.11ng/mL). The estrus to ovulation interval was significantly (P<0.05) greater when the P4 concentration was >1ng/mL on the day of estrus (36.17±0.73h in natural and 37.57±4.32h in synchronised) compared to <1ng/mL (31.28±1.74h in natural and 28.83±3.61h in synchronised). Taken together, the spinnbarkeit value and arborization pattern of cervical mucus had strong relationship with plasma P4 concentration and ovulation time indicating that the parameters could be used as a tool to decide optimal time of insemination in Sahiwal cattle.

Effect of interval between inseminations when using frozen-thawed boar sperm on fertility and fetal paternity in mature gilts

Multiple artificial inseminations (AI) are used in swine to compensate for variation in time of ovulation and following each insemination, a uterine immune response occurs to remove dead and damaged sperm. There are more dead and damaged sperm inseminated with use of frozen-thawed-semen (FTS) and closer insemination intervals are required to compensate for the reduced lifespan of the sperm. Therefore, the objectives of this experiment were to evaluate the effect of interval between inseminations and estrus to ovulation interval (EOI) on fertility and the impact of each AI using fetal paternity in mature gilts when using FTS. Semen from 11 boars was collected and frozen in 0.5mL straws at 1.4×109cells/mL. Time of estrus was synchronized in gilts (n=191) using Matrix® and assigned at estrus to AI treatment: (1) AI at a 4h interval (34 and 38h); (2) AI at an 8h interval (30 and 38h); or (3) AI at a 16h interval (22 and 38h). Ultrasonography was performed to determine time of ovulation. In each treatment, the first and second AI were from unique sires to allow for paternity identification using microsatellite markers. Each sire was represented across first and second inseminations. Gilts received an AI with 2×109 motile FTS in 80mL of extender. Pregnancy rate and litter size were assessed at slaughter on Day 33 following AI. Interval between inseminations affected pregnancy rate (P<0.01) with AI intervals of 8 (80%) and 16h (75%) greater than the 4h interval (55%). The EOI also affected pregnancy rate (P<0.001) with increased pregnancy rate for gilts having ovulations by 36h (85%) compared to those having ovulations by 24 (55%) and 60h (47%) but did not differ from those having ovulations at 48h (74%). Total fetuses (10.7), number of normal fetuses (10.2) and embryo survival (70.4%) were not affected by interval between inseminations or EOI (P>0.05). There was an interaction of treatment with EOI (P<0.05). Gilts inseminated at 8 or 16h intervals and with 36 or 48h EOI showed changes (P<0.05) in the proportion of offspring sired by the second AI while gilts inseminated at a 4h interval did not. The results of this study indicate that intervals between inseminations and time of ovulation each affects pregnancy rates but not litter size, but interacts to affect the proportion of offspring sired by the second insemination. This study suggests no detrimental effect of reduced amount of time between inseminations on the fertility of sperm used in a second insemination. For practical application, in a twice daily estrous detection and double AI, the greatest pregnancy rates occur when inseminations are spaced at 8 or 16h intervals to compensate for variation in ovulation.

An individual reproduction model sensitive to milk yield and body condition in Holstein dairy cows

To simulate the consequences of management in dairy herds, the use of individual-based herd models is very useful and has become common. Reproduction is a key driver of milk production and herd dynamics, whose influence has been magnified by the decrease in reproductive performance over the last decades. Moreover, feeding management influences milk yield (MY) and body reserves, which in turn influence reproductive performance. Therefore, our objective was to build an up-to-date animal reproduction model sensitive to both MY and body condition score (BCS). A dynamic and stochastic individual reproduction model was built mainly from data of a single recent long-term experiment. This model covers the whole reproductive process and is composed of a succession of discrete stochastic events, mainly calving, ovulations, conception and embryonic loss. Each reproductive step is sensitive to MY or BCS levels or changes. The model takes into account recent evolutions of reproductive performance, particularly concerning calving-to-first ovulation interval, cyclicity (normal cycle length, prevalence of prolonged luteal phase), oestrus expression and pregnancy (conception, early and late embryonic loss). A sensitivity analysis of the model to MY and BCS at calving was performed. The simulated performance was compared with observed data from the database used to build the model and from the bibliography to validate the model. Despite comprising a whole series of reproductive steps, the model made it possible to simulate realistic global reproduction outputs. It was able to well simulate the overall reproductive performance observed in farms in terms of both success rate (recalving rate) and reproduction delays (calving interval). This model has the purpose to be integrated in herd simulation models to usefully test the impact of management strategies on herd reproductive performance, and thus on calving patterns and culling rates.

Effect of a Single Injection of Long-acting Progesterone on the First Ovulation in Early and Late Spring Transitional Mares

Since 1966, exogenous progestins have been used in equine practice for pregnancy maintenance, estrous suppression, and control of erratic sexual behavior. This study was designed to investigate the use of a new compounded controlled-release progesterone preparation (BioRelease P4 LA 300) in early and late spring transitional mares. In the first experiment, the pharmacodynamic properties of the preparation were studied in five geldings. In the second experiment, the use of a single intramuscular injection (600 mg) was tested in 68 embryo-recipient mares maintained under natural photoperiod in the Southern Hemisphere. Experiment 1 demonstrated elevated serum concentrations of progesterone (>1 ng/mL) for 7.6 ± 2.2 days. In experiment 2, there was no effect of treatment in mares that were treated on September 18, independent of their follicular status at day of treatment (10 to 15 mm; 20 to 25 mm, respectively). When mares with a follicular size of 20 to 25 mm were treated on October 14, significantly more progestin-treated mares (10/12; 83%) ovulated between 10 and 24 days after treatment than untreated controls (3/12; 25%) ( P < .05). Additionally, there was a trend in mares treated on October 14 for a shorter treatment to ovulation interval (mean ± SD, 18.6 ± 8.7 days) compared with untreated controls (mean ± SD, 26.7 ± 14.7 days) ( P = .07). Administration of one single injection of long-acting progesterone is a simple and effective method of controlling the first ovulation of the season in late transitional mares.

Improved Prediction of Ovulation Time may Increase Pregnancy Rates to Artificial Insemination in Lactating Dairy Cattle

A prospective observational study was conducted in two Australian dairy herds to assess the potential for improving pregnancy rates (proportions of inseminations that result in pregnancy) to artificial insemination (AI) if the time of ovulation could be predicted with more certainty. Herd 1 calved year-round and inseminations were performed during two periods each day. Herd 2 calved during autumn-winter and inseminations were performed only after the morning milking each day. In both herds, the AI to ovulation interval of enrolled cows was determined by trans-rectal ovarian ultrasonography approximately 0, 12, 24 and 36 h after AI, and pregnancy was assessed by palpation per rectum 35-56 days after AI. Also, in Herd 1 vaginal electrical resistance (VER) measurements were taken at approximately 0, 12, 24 and 36 h after AI, and in Herd 2 cows were fitted with neck mounted activity meters that monitored cow activity count in 2-h periods. There was substantial variation in the intervals from AI to ovulation within and between herds (mean ± SD 21.2 ± 10.7, n = 102; 14.7 ± 10.4, n = 100 in herds 1 and 2, respectively). Pregnancy rates were higher for inseminations close to, but preceding, ovulation. Using combined herd data (n = 202), the highest pregnancy rate (50.8%) was observed for inseminations between 0 and 16 h before ovulation, a period in which only a modest proportion of inseminations (31.2%) occurred. In contrast, pregnancy rate was significantly lower (28.7%; risk ratio 0.6; 95% CI 0.4-1.0; p = 0.039) for inseminations between 16 and 32 h before ovulation, a period where the highest proportion of inseminations (53.2%) occurred. Thus pregnancy rates could potentially be improved if a greater proportion of inseminations were conducted shortly before ovulation. In Herd 1, mean VER during the peri-ovulatory period varied with time from ovulation. Lowest values (mean ± SEM, VER = 64.8 ± 1.2, n = 55) occurred approximately 18 h before ovulation and were significantly lower than measurements approximately 6 h before ovulation (67.4 ± 1.0; n = 73; p = 0.003). Further work is required to determine if VER can be used to identify ovulation time and hence the optimal time to inseminate in individual animals. In Herd 2 a modest proportion of inseminations (26.9%) occurred between 24 and 40 h after the onset of increased cow activity where the highest pregnancy rate (67.9%) was observed, whereas a significantly lower pregnancy rate (42.4%; risk ratio 0.6; 95% CI 0.4-0.9; p = 0.036) was observed for inseminations between 8 and 24 h after the onset of increased cow activity where the highest proportion of inseminations (56.7%) occurred. Thus cow activity monitoring may be useful to identify the optimal time to inseminate cows. Results from this study indicate that improved methods of ovulation prediction may allow better insemination timing relative to ovulation and consequently increased pregnancy rates.

Naturally occurring mastitis effects on timing of ovulation, steroid and gonadotrophic hormone concentrations, and follicular and luteal growth in cows

The effects of naturally occurring subclinical chronic or clinical short-term mastitis on time of ovulation, plasma steroid and gonadotropin concentrations, and follicular and luteal dynamics were examined in 73 lactating Holstein cows. Cows were sorted by milk somatic cell count and bacteriological examination into an uninfected group (n=22), a clinical mastitis group (n=9; events occurring 20±7 d before the study), and a subclinical chronic mastitis group (n=42). In addition, uninfected and mastitic cows were further sorted by their estrus to ovulation (E-O) interval. About 30% of mastitic cows (mainly subclinical) manifested an extended E-O interval of 56±9.2h compared with 28±0.8h in uninfected cows and 29±0.5h in the other 70% of mastitic cows. In mastitic cows with extended E-O interval, the concentration of plasma estradiol at onset of estrus was lower than that of uninfected cows or mastitic cows that exhibited normal E-O intervals (3.1±0.4, 5.8±0.5, and 5.5±0.5 pg/mL, respectively). The disruptive effect of mastitis on follicular estradiol probably does not involve alterations in gonadotropin secretion because any depressive effects of mastitis on pulsatile LH concentrations were not detected. Cortisol concentrations did not differ among groups. The preovulatory LH surge in mastitic cows with delayed ovulation varied among individuals, being lower, delayed, or with no surge noted compared with the normal LH surge exhibited by uninfected cows or mastitic cows with normal E-O interval (6.8±0.7 ng/mL). The diameter of the second-wave dominant follicle was larger and the number of medium follicles was smaller in uninfected and subclinical cows with normal intervals compared with subclinical cows with extended intervals (13.4±0.5 vs. 10.9±0.9mm, and 3.8±0.2 vs. 6.7±0.14 follicles, respectively). Mid-luteal progesterone concentrations were similar in uninfected and mastitic cows. These results indicate for the first time that around 30% of cows with subclinical chronic mastitis exhibit delayed ovulation that is associated with low plasma concentrations of estradiol and a low or delayed preovulatory LH surge.

175 REPRODUCTIVE PERFORMANCE OF MANGALARGA MARCHADOR MARES AFTER INDUCTION OF OVULATION WITH hCG OR DESLORELIN

The use of biotechnology, such as AI, embryo transfer, and hormonal protocols, have accelerated the genetic improvement in the equine specie, and inducers of ovulation, such as hCG, are important tools in implementing them. However, the repeated use of ovulation inducers can promote the development of antibodies and undermine their purpose. Thus, a synthetic GnRH, deslorelin, has been used. In this study, we compared the reproductive performance of 44 Mangalarga Marchador donor mares, aged between 5 and 21 years and with sound reproductive history after treatment with hCG or deslorelin. During estrus, mares were examined by transrectal ultrasonography every other day until a follicle of 30 mm in diameter was detected and then daily until detection of a &gt;35-mm follicle and moderate uterine edema. At this time, mares were treated with either 2 mL of saline, i.m. as controls (CON = 16); 2500IU of hCG, i.v. (Chorulon, Intervet Inc., Millsboro, DE, USA; hCG = 14); or 2 mg mL-1 deslorelin in BRT vehicle (BET Pharm, Lexington, KY, USA), i.m. (DES = 14). After treatments, mares were examined at 12-h intervals until ovulation and were inseminated with fresh semen 12 h after ovulation. On Day 8, embryos were recovered and evaluated. All mares were ovulated, and follicle diameters were not different (P &gt; 0.05) at the time of treatment (38 ± 0.029 v. 39 ± 0.029 v. 38 ± 0.029 mm). Embryo recovery was similar among groups (CON, 37.5%; hCG, 42.8%; DES, 50.0%, respectively). The interval from treatment to ovulation did not differ (P &gt; 0.05) between hCG (1.43 +0.56 days) and DES mares (1.14 + 0.36 days), and both were less (P &gt; 0.05) than for controls (CON, 2.94 + 0.77 days). The number of mares that ovulated per ovulation interval were as follows: &lt;24 h = CON: 0%, hCG: 7.14%, and DES: 14.29%, respectively; from 24 to 48 h = 6.25%, 64.29%, and 78.57%; from 49 to 72 h = 37.5%, 28.57%, and 7.14%; &gt;72 h = 56.25%, 0%, and 0%. Time to ovulation was negatively correlated (P &lt; 0.05) with follicle diameter in CON (r = -0.50, P &lt; 0.05) but not for hCG (r = 0.05) or DES (r = 0.022) and was positively correlated with embryo recovery for DES (r = 0.46, P &lt; 0.10), but not hCG (r = 0.23) or CON (r = 0.09). Based on the results, we concluded that hCG and DES effectively synchronize the time of ovulation. Follicle size did not affect the time of ovulation in hCG- and DES-treated mares. We thank the Farm Water supply for the animals and drugs.

Aspiration of equine oocytes from immature follicles after treatment with equine pituitary extract (EPE) alone or in combination with hCG

This study examined the effect of treating mares with equine pituitary extract (EPE) alone or in combination with hCG on the recovery rate of immature follicles by transvaginal follicular aspiration (ovum pick-up; OPU). Ten normally cycling crossbred mares aged 3–15 years and weighing 350–400 kg were subjected to each of three treatments in a random sequence with each exposure to a new treatment separated by a rest cycle during which a spontaneous ovulation occurred. The treatments were (1) superovulated with 25 mg EPE and treated with 2500 IU hCG, (2) superovulation with 25 mg EPE, and (3) control (no exogenous treatment). Treatments 7 days after spontaneous ovulation; and all the follicles >10 mm were aspirated 24 h after the largest follicle achieved a diameter of 27–30 mm for control group, and most follicles reached 22–27 mm for the EPE alone treatment. To the group EPE + hCG, when the follicles reached 22–27 mm, hCG was administered, 24 h before OPU. Superovulation increased the number of follicles available for aspiration. The total number of follicles available for aspiration was 61 in the EPE/hCG group, 63 in the EPE group and 42 in the control. The proportion of follicles aspirated varied from 63.5% to 73.8%. Oocyte recovery rate ranged from 15.0% to 16.7% and the proportion of mares that yielded at least one oocyte was 70% (7/10) in the EPE/hCG, 60% (6/10) in the EPE alone and 50% (5/10) in control group. The EPE/hCG treatment had a higher proportion of follicles with expanded granulose cells (64.4%) than the control (3.3%; p < 0.05) and the EPE treatment (25.0%). The intervals from spontaneous ovulation to aspiration were similar for all treatments (11–12 days). However, superovulatory treatment significantly increased the aspiration to ovulation interval from 15 ± 4 days for control to 27 ± 15 days for EPE ( p < 0.05) and to 23 ± 13 days for EPE/hCG treatment with commensurate increases in the time between spontaneous ovulations.

Exposure to endotoxin during estrus alters the timing of ovulation and hormonal concentrations in cows

The effect of intramammary (IMM) or intravenous (IV) administration of E. coli endotoxin (LPS), at the onset of estrus, at the time of ovulation was examined. Steroid and gonadotropin concentrations around ovulation were also determined. Lactating Holstein cows ( n = 33) were assigned to saline-controls ( n = 12) and treated with LPS-IV (0.5 μg/kg; n = 13) or LPS-IMM (10 μg; n = 8). Synchronized cows were observed continuously for estrus. LPS (or saline) was injected within 30 min from the onset of standing estrus, at peak estradiol concentrations. The typical rise of body temperature, somatic cell count, cortisol, and NAGase activity was noted. One-third of both LPS-IV- and LPS-IMM-treated cows were manifested by an extended estrus to ovulation (E–O) interval of around 75 h or did not ovulate, compared with about 30 h in the other 2/3 of LPS cows and all controls. Estradiol concentrations 24 h before and after LPS did not differ between groups. However, LPS-IV cows with extended intervals exhibited another estrus and an additional rise of estradiol followed by delayed ovulation. LPS-treated cows with a delayed E–O interval had low or delayed LH surge; two LPS-treated cows did not exhibit LH surge and did not ovulate. All control cows exhibited normal hormone levels. Delayed ovulation was associated with a delayed rise of luteal progesterone. The results indicated that exposing cows to endotoxin during estrus induced a decreased and delayed LH surge in one-third of the cows. This was associated with delayed ovulation, which reduces the chances of successful fertilization.

Melengestrol acetate as a tool for inducing early ovulation in transitional mares

The efficacy of melengestrol acetate (MGA) to shorten the vernal transition of mares by synchronising and accelerating the first ovulation of the year after 60 days of phototherapy was determined by ultrasonographic monitoring. Sixteen mares in late transition were fed two doses of MGA (150 mg/mare/day and 100 mg/mare/day, respectively) for 10 days. A luteolytic dose of prostaglandin was administered to each mare one day after the end of MGA treatment. The presence and duration of oestrus, follicular growth, uterine oedema and presence of ovulation were monitored by ultrasonography and the cervical tone was evaluated by rectal palpation. Ovulation was detected in 87.5% of the mares treated with 150 mg MGA/mare/day for 10 days, and in 62.5% of the mares receiving 100 mg MGA/mare/day for 10 days. This was statistically different (P = 0.03) from the untreated control mares having an ovulation rate of 20%. Mares that received 150 mg MGA/day for 10 days had a mean treatment to ovulation interval of 13.1 +/- 5.97 days after the end of treatment, while mares that received 100 mg MGA/day for 10 days had a mean of 25.6 +/- 10.50 days (P = 0.01) to ovulation. These results suggest that MGA can be used for synchronising and hastening the first ovulation of the year in mares.

Time of ovulation in nulliparous and multiparous goats

Fifteen nulliparous and nine multiparous Serrana goats were used, through two successive oestrous cycles, in order to characterize their ovulation time with regard to the number of ovulations after induced and natural oestrus during the breeding season. The onset of oestrus was detected by the amount of vasectomized bucks after oestrus synchronization with prostaglandin, given 10 days apart, and in the following two expected natural oestrus. The preovulatory LH peak was determined from blood samples collected 0, 4, 8, 12, 16, 20 and 24 h after onset of oestrus. A transrectal ovarian ultrasound scanning was performed 20, 24, 28, 32, 36, 40, 44 and 60 h after onset of oestrus, for the detection of ovulations by means of the disappearance of large follicles (>4 to 5 mm). Single ovulations were observed in 76% of oestrous periods in nulliparous goats and in 18% of nulliparous goats. The onset of oestrus to LH peak interval was lower in nulliparous (12.1 ± 0.9 h, n = 38) than in multiparous (15.6 ± 1.0 h, n = 22, P < 0.05) goats with no oestrus interaction effects (P > 0.05). The LH peak to first ovulation interval was higher after natural (18.9 ± 0.7 h, n = 36) than after induced (15.8 ± 1.2 h, n = 24, P < 0.05) oestrus. The onset of oestrus to total ovulation interval was influenced by parity (P < 0.01) and oestrus type (P < 0.05) with a length of 30.1 ± 1.1 h (n = 15) and 33.4 ± 1.5 h (n = 9) for induced oestrus of nulliparous and multiparous goats, respectively, and 32.5 ± 1.0 h (n = 23) and 36.5 ± 1.1 h (n = 13) for natural oestrus of nulliparous and multiparous goats, respectively. The onset of oestrus to first ovulation interval was not influenced by parity, but an interval of 8.0 ± 1.6 h was observed between the first and second ovulations in polyovulatory oestrus. Consequently, nulliparous goats that are predominantly monovular ovulate earlier than multiparous goats that are predominantly polyovulatory. In conclusion, significant differences occurred in the number and time of ovulations between nulliparous and multiparous goats. More research is necessary for a deeper understanding of the mechanisms regulating monovularory and polyovulatory oestrous cycles regarding the parity of goats.

Gestational Length and First Postpartum Ovulation of Criollo Mares on a Stud Farm in Southern Brazil

Abstract The Criollo horse industry requires more efforts toward a better understanding of breed characteristics and physiology; few studies have been conducted in Criollo horses to fulfill this demand. Toward this aim, 70 Criollo mares (between 3 and 28 years of age) underwent physiologic evaluation of the length of gestation, occurrence of foal heat, and interval to postpartum ovulation. Gestation length in the 70 mares was 335.6 ± 10.5 days, varying from 312 to 364 days. The mean (±SD) interval from parturition to first ovulation of 42 mares that foaled between September and December of 2005 and 2006 was 19.9 ± 14.0 days. Eighty-three percent of the mares had an interval to foal heat ovulation shorter than 20 days (35/42). The mean (±SD) parturition to ovulation interval of these mares was 14.2 ± 3.0 days.

Interaction of calf suckling, use of oxytocin and milk yield with reproductive performance of dairy buffaloes

Calf suckling and oxytocin injections are commonly used for pre-milking stimulus in dairy buffaloes under field conditions. A study was conducted to investigate effect of these treatments on reproductive performance. Fifty one Nili-Ravi buffaloes were monitored from parturition up to 150 days postpartum through rectal examination. Data on milk yield, body condition score (BCS) and reproductive parameters were recorded weekly. Postpartum ovulation interval (POI) was determined by presence of an ovulation depression or a very soft corpus luteum haemorrhagicum and was confirmed through milk progesterone levels (MPL). Suckling was used to stimulate milk let down, and where the calf had died, injection of oxytocin was resorted to. Milk samples were analyzed for MPL using radioimmunoassay (RIA) and fat; and milk yield was converted to 4% fat corrected milk (FCM). The mean postpartum uterine involution length (PUI) was 34.30 ± 1.33 days. Mean POI was 59.37 ± 4.76 days and mean postpartum estrus interval (PEI) was 69.03 ± 6.03 days. Suckling period averaged 26.40 ± 5.57 days and correlated with POI ( r = 0.19, P < 0.01) and PEI ( r = 0.23, P < 0.01). POI was shortest in buffaloes suckled for one month ( P < 0.05). Oxytocin was used with a mean dosage of 7.50 IU, delaying placental expulsion time (PET) and POI but shortening PEI. BCS shortened PET, POI and PEI ( P < 0.01). Mean FCM was 14.50 ± 0.20, ranging from 2 to 35 kg/d; and was higher in estrus group; correlating positively with POI ( r = 0.31, P < 0.01). MPL were 1.37 ± 0.17 ng/ml and increased after ovulation, remaining greater than 1.5 ng/ml from Day 4 to 14 of the estrus cycle, followed by a rapid decline up to next estrus. BCS in buffaloes resuming oestrus was constantly higher than those failing to resume ovarian cyclicity. Live weight, prepartum was 510.0 ± 5.9 kg with a loss of 3.7 ± 2.12 kg, 30 days postpartum. The present study suggests a lower reproductive efficiency of dairy buffaloes under the peri-urban farming system reflected by ovarian cyclicity in 68.63% buffaloes within 150 days postpartum and silent estrus in 51.5% of the cases. Increasing suckling duration and use of oxytocin delayed POI, however, POI was shortest in buffaloes suckled for one month. The high yielding buffaloes also manifested better reproductive cyclicity; while moderate yielder showed shorter ovulation intervals and higher conception rate.