Manipulation and control of the estrous cycle in pasture-based dairy cows

Treatments designed to synchronize luteolysis, preovulatory follicular development, and ovulation, and resynchronize estrus after a first AI have improved responses to synchronization treatments. Protocols based only on the use of PGF result in variable onset of estrus. Concentrations of progesterone prior to administering PGF have affected submission rates and fertility while administration of estradiol benzoate (EB) after inducing luteolysis has improved the synchrony of estrus and ovulation in some studies. In pasture-based dairy cows, GnRH-based protocols have generally resulted in one-third of both anestrous and cycling cows conceiving following synchronization of ovulation and timed AI. Protocols which use intravaginal progesterone releasing inserts (IVP4) are effective in inducing estrus in over 90% of treated dairy cows. Resynchronization of estrus after reinsertion of an IVP4 also improves the synchrony of returns to estrus, but pregnancy rates to the first AI have been reduced in some studies, and submission rates at a resynchronized estrus are less than at the first synchronized estrus. Administration of EB can be used to synchronize follicle wave emergence in resynchronized cows with intervals to new wave emergence comparable to that in cows synchronized for a first AI, but plasma concentrations of progesterone following treatment may be reduced. Synchronization of estrus and ovulation can be enhanced by administration of EB or GnRH during proestrus, but dose, timing and stage of follicular development at the time of treatment can affect outcomes.     

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.     

Comparison of endocrine changes,timing of ovulations,ovarian follicular growth,and efficacy associated with Estradoublesynch and Heatsynch protocols in Murrah buffalo cows (Bubalus bubalis)

Poor estrus expression and the difficulty encountered in predicting the time of ovulation compromise the reproductive efficiency of Murrah buffalo cows. Synchronization of ovulation and timed artificial insemination are able to precisely control the time of ovulation and thus avoid the need for estrus detection. Recently, the Estradoublesynch protocol (administration of a PGF2α injection 2 days before Heatsynch protocol; GnRH 0, PGF2α 7, estradiol benzoate [EB] 8) was developed that precisely synchronized ovulation twice, i.e., after GnRH and EB injections and resulted in satisfactory pregnancy rates in Murrah buffaloes. The present study was conducted on 104 cycling and 31 anestrus buffaloes to compare (1) the endocrine changes, timing of ovulations, ovarian follicular growth, and efficacy of Estradoublesynch and Heatsynch protocols in cycling and (2) the efficacy of Estradoublesynch and Heatsynch protocols for the improvement of fertility in cycling and anestrus Murrah buffalo cows. Ovulation was confirmed after all GnRH and EB treatments by ultrasonographic examination at 2-hour intervals. Plasma progesterone and total estrogen concentrations were determined in blood samples collected at daily intervals, beginning 2 days before the onset of protocols until the day of second ovulation detection. Ovulatory follicle size was measured by ultrasonography at six time points (first PGF2α administration of Estradoublesynch protocol every 2 days before the onset of Heatsynch protocol, GnRH administration of both protocols, 2 hours before ovulation detection after GnRH administration of both protocols, second PGF2α injection of Estradoublesynch protocol, PGF2α injection of Heatsynch protocol, EB injection of both protocols and, 2 hours before ovulation detection after EB administration of both protocols). Plasma LH, total estrogen, and progesterone concentrations were determined in blood samples collected at 30-minute intervals for 8 hours, beginning GnRH and EB injections, and thereafter at 2-hour intervals until 2 hours after the detection of ovulation. The first ovulatory rate was significantly higher (P < 0.05) in the Estradoublesynch protocol (84.6%) than that in the Heatsynch protocol (36.4%). The first LH peak concentration (74.6 ± 10.4 ng/mL) in the Estradoublesynch protocol was significantly higher (P < 0.05) than that of the Heatsynch protocol (55.3 ± 7.4 ng/mL). In Estradoublesynch protocol, the total estrogen concentration gradually increased from the day of GnRH administration coinciding with LH peak, and then gradually declined to the basal level until the time of ovulation detection. However, in Heatsynch protocol, the gradual increase in total estrogen concentration after GnRH administration was observed only in those buffalo cows, which responded to treatment with ovulation. In both Estradoublesynch and Heatsynch protocols, ovulatory follicle size increased by treatment with GnRH and EB until the detection of ovulation. The pregnancy rate after the Estradoublesynch protocol (60.0%) was significantly higher (P < 0.05) than that achieved after the Heatsynch protocol (32.5%). Satisfactory success rate using the Estradoublesynch protocol was attributed to the higher release of LH after treatment with GnRH, leading to ovulation in most of the animals and hence creating the optimum follicular size at EB injection for ovulation and pregnancy to occur.     

The cow as an induced ovulator: Timed AI after synchronization of ovulation

Timed-AI after synchronization of ovulation has become one of the most used reproductive technologies developed during the past 40 years. Various adaptations of this technology are now extensively used worldwide, in the beef and dairy cattle industry. Our well-cited report, published in Theriogenology in 1995, presented a method termed Ovsynch, that used GnRH and PGF_2α to perform synchronization of ovulation and timed AI in lactating dairy cows. This report introduced Ovsynch, more as a concept of induced ovulation, and demonstrated the ovarian dynamics during the protocol. Validation and improvements on this method were subsequently performed in numerous university studies and on commercial dairies, worldwide. This review will provide a brief historical background, some personal recollections, and certain modifications that have been made in synchronization of ovulation protocols. Each section emphasizes the physiology that underlies the most widely-used synchronization of ovulation protocols and key modifications and some practical application of these protocols on commercial operations. Finally, the effect of timed AI in the US dairy industry and in the Brazilian beef cattle industry are compared. Although numerous studies have been done using these protocols, there is still substantial need for research to improve the synchronization, efficacy, simplicity, and practical application of these protocols.     

When is a cow in estrus? Clinical and practical aspects

Good detection of estrus is critically important in dairy husbandry. Incorrect detection of estrus is related to loss of profit due to extended calving intervals, milk loss, veterinary costs, etc. Detection of estrus remains a major problem despites enormous progress in the knowledge of reproductive physiology of the cow and in development of estrus detection aids. To achieve good estrus detection, many factors have to be taken into account. On one hand a cow has to express estrus and on the other hand the farmer has to detect it. Combined action of several hormones causes physiological changes that lead to ovulation and an environment in the uterus that allows sperm to fertilize the egg. Besides these internal actions, a number of external changes can be observed. When using visual observations, time of the day and time spend on observation have a great impact on detection rates. Many devices are available to aid in estrus detection, such as pedometers, mount devices, temperature, and hormone measurements.Expression of estrus can be influenced by many factors. Heritability, number of days postpartum, lactation number, milk production, and health are known to influence estrus expression. Environmental factors like nutrition, season, housing, herd size, etc. also play a role in estrus expression. To evaluate estrus detection, record keeping is very important; a number of formulas can be used to assess detection efficiency. Besides the farmer, the veterinarian and inseminator can play an important role in estrus confirmation and good insemination strategy. In the end, the time of ovulation and the age of the egg at sperm penetration is critical for conception. Therefore, emphasis in research needs to be on the timing of insemination relative to ovulation, and thus on the detection of ovulation.     

Efficacy of four synchronization protocols on the estrus behavior and conception in native Korean cattle (Hanwoo)

Ineffective estrus detection is the foremost limiting factor in the fertility of farmed cattle worldwide. Failure to detect estrus or erroneous diagnosis of estrus results in great economic losses in Korea each year. This study was carried out in order to comprehensively describe the estrus behaviors and conception rates of different estrus synchronization protocols applied to 40 cycling native Korean cattle (Hanwoo). The cows were grouped into four (n = 10) and treated with the following protocols: (1) Day -15: controlled intravaginal drug-releasing device (CIDR) for 12 days; Day -5: prostaglandin F_2α (PGF_2α), (2) ovulation synchronization (OVS): Day -15: GnRH; Day -6: PGF_2α; Day -4: GnRH, (3) Day -15: progesterone-releasing intravaginal device for 12 days; Day -5: PGF_2α; and (4) Day -15: PGF_2α; Day -4: PGF_2α. Artificial insemination was performed 12 hours after the detection of estrus using frozen-thawed semen. Estrus signs were compared using a charge-coupled device camera (CCDC) and a control method (direct visual observation). The pregnancy of the cows was determined by transrectal ultrasonography at Days 25 to 30 postinsemination. The results indicated that the day of estrus return was significantly earlier using the CCDC method compared with direct visualization (P < 0.05). Mounting of other cows was the most predominant sign of estrus among the flock (P < 0.05), as analyzed using the CCDC. In the OVS group, a lower rate of mounting was observed than in the other three groups. Moreover, significantly fewer estrus behaviors were noticed in the OVS protocol group (P < 0.05). Both first service conception and overall conception rates were significantly higher (P < 0.05) in the CIDR and OVS treatment groups. In conclusion, the CIDR and OVS protocols appear to be the best practice for the synchronization of estrus for reproductive competence through the CCDC in Hanwoo cows. However, CIDR has a practical advantage over OVS with respect to estrus detection.     

Managing the dominant follicle in lactating dairy cows

Reproductive efficiency is not optimal in high-producing dairy cows. Although many aspects of ovarian follicular growth in cows are similar to those observed in heifers, there are numerous specific differences in follicular development that may be linked with changes in reproductive physiology in high-producing lactating dairy cows. These include: 1) reduced circulating estradiol (E2) concentrations near estrus, 2) ovulation of follicles that are larger than the optimal size, 3) increased double ovulation and twinning, and 4) increased incidence of anovulation with a distinctive pattern of follicle growth in anovular dairy cows. The first three changes become more dramatic as milk production increases, although anovulation has not generally been associated with level of milk production. To overcome reproductive inefficiencies in dairy cows, reproductive management programs have been developed to synchronize ovulation and enable the use of timed AI in lactating dairy cows. Effective regulation of the CL, follicles, and hormonal environment during each part of the protocol is critical for optimizing these programs. This review discusses the distinct aspects of follicular development in lactating dairy cows and the methodologies that have been utilized in the past two decades in order to manage the dominant follicle during synchronization of ovulation and timed AI programs.     

Managing the dominant follicle in lactating dairy cows

Reproductive efficiency is not optimal in high-producing dairy cows. Although many aspects of ovarian follicular growth in cows are similar to those observed in heifers, there are numerous specific differences in follicular development that may be linked with changes in reproductive physiology in high-producing lactating dairy cows. These include: 1) reduced circulating estradiol (E2) concentrations near estrus, 2) ovulation of follicles that are larger than the optimal size, 3) increased double ovulation and twinning, and 4) increased incidence of anovulation with a distinctive pattern of follicle growth in anovular dairy cows. The first three changes become more dramatic as milk production increases, although anovulation has not generally been associated with level of milk production. To overcome reproductive inefficiencies in dairy cows, reproductive management programs have been developed to synchronize ovulation and enable the use of timed AI in lactating dairy cows. Effective regulation of the CL, follicles, and hormonal environment during each part of the protocol is critical for optimizing these programs. This review discusses the distinct aspects of follicular development in lactating dairy cows and the methodologies that have been utilized in the past two decades in order to manage the dominant follicle during synchronization of ovulation and timed AI programs.     

Effect of subclinical uterine infection on cervical and uterine involution, estrous activity and fertility in postpartum buffaloes

Nili-Ravi buffaloes (n=29) that calved normally between August and November and did not develop any clinical reproductive disorder after calving were studied for the incidence of sub-clinical bacterial infection of the uterus and its effects on postpartum reproductive efficiency. The incidence of subclinical uterine infection was 24% (7/29). Involution of the cervix and uterus was slower (P < 0.01) in the infected group than in the normal group (45.6 vs 31.1 days and 46.3 vs 35.8 days), respectively. The mean diameters of cervix and gravid horn on Day 12 post partum and on completion of involution did not differ between buffaloes of the two groups. However, the rate of involution of the cervix and the gravid horn was lower in buffaloes of the infected group (2.2 vs. 2.7 mm/day and 2.6 vs. 3.2 mm/day). The mean interval to first post partum ovulation was similar in buffaloes in the infected (35.5 days) and the normal group (33.8 days). The life span of corpus luteum formed after first ovulation was shorter (11 days) in buffaloes of both groups than that of a normal estrous cycle (15 to 17 days). The incidence of silent ovulation was apparently higher in buffaloes of the infected group (83 vs. 60%) but the difference was not significant. For the first four months after calving, the mean interval to first postpartum estrus was longer in buffaloes of the infected group (73.0 vs. 47.7 days; P < 0.01). Similarly, the average service period was longer in buffaloes of the infected group (91.0 vs. 64.8 days; P < 0.05). The overall pregnancy rate for the first four months after calving did not differ between buffaloes of the two groups. We conclude that subclinical bacterial infection of the postpartum uterus delays the cervical and uterine involution which can, in turn, delay the occurrence of first postpartum estrus and prolong the service period in buffaloes.     

Timed embryo transfer programs for management of donor and recipient cattle

Currently, timed ovulation induction and fixed-time artificial insemination (FTAI) in superstimulated donors and synchronization protocols for fixed-time embryo transfer (FTET) in recipients can be performed using GnRH or estradiol plus progesterone/progestin (P4)-releasing devices and prostaglandin F_2α (PGF2α). The control of follicular wave emergence and ovulation at predetermined times, without estrus detection, has facilitated donor and recipient management. However, because Bos taurus cows have subtle differences in their reproductive physiology compared with Bos indicus cattle, one cannot assume that similar responses will be achieved. The present review will focus on the importance of orchestrating donor and recipient management to assure better logistics of procedures to achieve more desirable results with embryo collection and transfer. In addition, this will provide clear evidence that the use of FTAI in superstimulated donors and FTET in embryo recipients eliminates the need to detect estrus with satisfactory results. These self-appointed programs reduce labor and animal handling, facilitating the use of embryo transfer in beef and dairy cattle.     

Synchronization of estrus in goats: the relationship between time of occurrence of estrus and fertility following artificial insemination

The fertility rate for goats following artificial insemination (AI) is usually analyzed according to herd or treatment groups. However, these general information are insufficient to allow identification of specific factors which affect this individual reproductive performance. In the present experiment 640 dairy goats were used to analyze to what extent the interval from sponge removal to estrus affects the results of AI, performed at a predetermined time following sponge removal. Estrus occurred in 98.1% of experimental animals between 24 and 72 hours after sponge removal. The fertility rate was lower for goats that came into estrus later than 30 hours after sponge removal (33.3%, n = 108 than for goats that exhibited estrus earlier (65.0%, n = 520; P<0.001). The occurrence of late estrus is not age dependent, but it increases with the number of treatments that an individual animal has previously received. These results show that the low fertility rate observed in some herds after synchronization of estrus and AI may be related to the high proportion of goats with a late occurrence of estrus, and this phenomenon increases in animals that are treated repeatedly.     

Fertility in South Australian commercial Merino flocks: relationships between reproductive traits and environmental cues

High levels of reproductive loss have been reported in commercial Merino flocks (n=68) from the cereal/livestock and high rainfall zones in South Australia (Kleemann DO, Walker SK. Fertility in South Australian commercial Merino flocks: sources of reproductive wastage. Theriogenology 2005;63:2075-88). Relationships between reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival) and environmental end points (liveweight, condition score, temperature at mating, chill index at lambing) are reported in this paper. They were analysed within season of mating (October to December; January to March) and age of ewe (maiden as 1.5-year-old, mature as older). Incidence of estrus was positively related (P<0.05) to condition score in the October to November interval. Return rate to service was positively (P<0.05) influenced and fertility was negatively (P<0.05) influenced by the number of days ambient temperatures were > or =32.0 degrees C during mating, indicating that high ambient temperatures may reduce embryo survival. Liveweight and, to a lesser extent, condition score, accounted for significant proportions of variation associated with ovulation rate (39.3 and 12.7%, respectively). Ovulations per 100 ewes increased by 1.8 per kg increase in liveweight over all flocks. Ovulatory response to liveweight increased (P<0.01) from the October to December to the January to March period of mating (1.5 versus 3.4 ovulations per kg, respectively). Overall, a flock's fertility and fecundity increased by 0.27 and 1.42% per kg increase in liveweight, respectively. Reproductive wastage from partial failure of multiple ovulations (PFMO) was positively related to liveweight (P<0.01) and ovulation rate (P<0.001). Survival of single lambs was positively and curvilinearly related to maternal liveweight and condition score measured in late pregnancy (P<0.05). Linear relationship of these variables for twin lamb survival was significant for condition score only. Single and twin lamb survival were also positively related to liveweight and condition score at mating (P<0.05). We concluded that nutritional cues have a major impact on reproductive traits in commercial Merino flocks in South Australia; it sets the potential number of lambs (ovulation rate) and influences survival of lambs as early as at mating. Indications are that high ambient temperatures may influence embryo survival. It is recommended that future research efforts focus on: (a) prenatal nutritional influences on the physiology of mother-offspring behaviours at birth; and (b) possible peri-conceptional dietary factors controlling embryo loss resulting from partial failure of twin ovulations, to improve reproductive efficiency in the Merino.     

Timed embryo transfer programs for management of donor and recipient cattle

Currently, timed ovulation induction and fixed-time artificial insemination (FTAI) in superstimulated donors and synchronization protocols for fixed-time embryo transfer (FTET) in recipients can be performed using GnRH or estradiol plus progesterone/progestin (P4)-releasing devices and prostaglandin F_2α (PGF2α). The control of follicular wave emergence and ovulation at predetermined times, without estrus detection, has facilitated donor and recipient management. However, because Bos taurus cows have subtle differences in their reproductive physiology compared with Bos indicus cattle, one cannot assume that similar responses will be achieved. The present review will focus on the importance of orchestrating donor and recipient management to assure better logistics of procedures to achieve more desirable results with embryo collection and transfer. In addition, this will provide clear evidence that the use of FTAI in superstimulated donors and FTET in embryo recipients eliminates the need to detect estrus with satisfactory results. These self-appointed programs reduce labor and animal handling, facilitating the use of embryo transfer in beef and dairy cattle.     

Effect of oestrus synchronization methods on oestrus behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes

The objective of this study was to determine the effect of oestrous synchronization methods on oestrous behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes. In Experiment 1, oestrous behaviour and timing of ovulation were determined from (n=34) oestruses. The mean (+/- S.E.M.) time of ovulation after the onset of standing oestrus was greater (P<0.05) in PGF(2alpha)-induced luteolysis (30.6+/-1.5h) compared to Ovsynch buffaloes (15.0+/-0.8h). In Experiment 2, pregnancy rates were compared between two methods of synchronization (detected oestrus and Ovsynch protocol) during the breeding and low breeding seasons. Pregnancy rates of buffaloes bred at detected oestrus (62.5%) or by the Ovsynch protocol (36.3%) during the breeding season did not differ significantly (P>0.05) from those which were inseminated during the low breeding season (55.5%) and (30.4%), respectively. This study demonstrates clearly that (1) timing of ovulation in Nili-Ravi buffalo is about 30h after the onset of standing oestrus and (2) buffaloes can be successfully synchronized with optimum fertility using either PGF(2alpha) alone (detected oestrus) or using (Ovsynch protocol) during low breeding season, to calve during the period when milk availability is short.     

Use of vaginal electrical resistance (VER) to predict estrus and ovarian activity, its relationship with plasma progesterone and its use for insemination in buffaloes

In three experiments we studied the baseline and changes in VER during different natural estrous cycle stages (n=146) in ovarian structures and in plasma progesterone during estrus induced by prostaglandin injection (n=16) and the VER at insemination (n=90) in an attempt to predict estrus, ovulation and the best VER range for inseminating buffaloes for optimum conception. The baseline VER was classified on the basis of ovarian findings and estrous cycle stages. The mean VER during estrus, metestrus, diestrus, proestrus and anestrus was 32.68 +/- 0.46, 41.26 +/- 1.17, 50.23 +/- 0.55, 43.20 +/- 0.64 and 55.86 +/- 0.57 ohms, respectively. There was a significant difference (P<0.01) between the VER except those between metestrus and proestrus. The ANOVA for VER over estrous cycle stages showed a highly significant (P<0.01) effect of stage of estrous cycle on VER in buffaloes. The percent decrease in VER was more pronounced from diestrus to estrus. In the second part of the study plasma progesterone profiles and the appearance of estrus in buffaloes induced to estrus using two dose schedules and routes of PGF2alpha administration showed that luteolysis and estrus induction was slower in the 10 mg i.v.s.m. route (Intra Vulvo Submucosal) (only 60% animals evinced estrus in 48 to 72 hours) as compared to the 25 mg i.m. route (83.33% evidenced estrus in 48 to 72 hrs). Fall in plasma progesterone was synchronous to a fall in VER, the correlation (0.65) between them being positive and significant (P<0.01). After ovulation the VER started rising, showing a distinct relationship between VER and ovulation. By using VER, an additional 36.6% of the buffaloes could be detected in estrus. In the third part of the study, insemination of buffaloes induced to estrus (n=11) and normal-estrus buffaloes (n=79) showed that the overall conception rates to single insemination when the buffaloes were inseminated at the VER range of 26 to 30, 31 to 35 and 36 to 40 ohms were 81.48, 58.97 and 16.66%, respectively. Buffaloes showing VER from 31 to 35 ohms and 36 to 40 ohms also evidenced atypical and Null fern pattern in the cervicovaginal mucus. The study proved that VER can be used successfully to predict the stage of estrous cycle, ovarian status and ovulation; and insemination at a low VER distinctly improves the conception rates in buffaloes.     

The effect of addition of equine chorionic gonadotropin to a progesterone-based estrous synchronization protocol in buffaloes (Bubalus bubalis) under tropical conditions

Poor estrus expression and anestrus decrease the reproductive efficiency of buffaloes. The objective of this study was to determine whether the addition of equine chorionic gonadotropin (eCG) to an estrous synchronization protocol and timed insemination could improve ovulation and pregnancy rates of anestrous buffalo cows under tropical conditions. The study population comprised 65 lactating Murrah buffalo cows which were assigned to CIDR (n = 33) or CIDR + eCG (n = 32) treatment groups. Cows in the CIDR group were fitted for 8 d with a controlled intravaginal drug release (CIDR) device containing 1.38 g progesterone, received GnRH (10 μg i.m.) on D 0, PGF_2α (750 μg i.m.) on D 7, and GnRH (10 μg i.m.) on D 9; whereas cows in the CIDR + eCG group received the same treatment plus eCG (500 IU, i.m.) at the time of PGF_2α treatment. All cows were inseminated 16-20 h after the second GnRH treatment. Blood samples were obtained 10 d before the start of synchronization treatment (Day -10) and at the onset of treatment (Day 0). Cows with plasma progesterone concentrations <1 ng/mL recorded in both samples (Low-Low levels of P4) were classified as non-cyclic cows. Similarly, when either one or both of the sample pair contained concentrations of serum progesterone ≥1 ng/mL (High-High, Low-High, or High-Low levels of P4), the buffaloes were classified as cyclic cows. Ovulation rate, defined as the number of buffaloes with at least one corpus luteum 10 days after insemination, was significantly higher (P = 0.018) in the CIDR + eCG (84.4%) cows than in the CIDR cows (57.6%). Pregnancy rate was numerically lower in CIDR (27.3%) than CIDR + eCG (40.6%) cows, though differences were not significant (P = 0.25). Pregnancy rates for CIDR + eCG cows were similar to that of cows inseminated after natural estrus (40.9%; 29/71). In the non-cyclic animals, higher ovulation rates (P = 0.026) were recorded for the CIDR + eCG (81%) than for the CIDR cows (47.4%). Our results indicate that the addition of eCG to a progesterone-based estrous synchronization regimen substantially improves the ovulation rate in non-cyclic buffaloes. When this treatment is followed by timed AI, pregnancy rates achieved in anestrous buffaloes, whether cyclic and non-cyclic, may approach the rates observed in cows inseminated at natural estrus.     

Reproduction in chinchilla (Chinchilla lanigera): current status of environmental control of gonadal activity and advances in reproductive techniques

In female swine, PGF2α is an important regulator of corpora luteal (CL) function, uterine contractility, ovulation, and embryo attachment. High affinity PGF2α receptors are present in the CL at all stages of the estrous cycle and they are functional. Therefore, a lack of luteolytic capacity of PGF2α is related to other factors that have not been well identified. In female pigs, a single exogenous PGF2α injection produces a short lasting decrease in plasma progesterone levels but does not induce luteolysis before day 12 of the estrous cycle. However, multiple injections of PGF2α can induce luteolysis before day 12 of the estrous cycle and may be utilized in the development of protocols for ovulation synchronization and timed AI. Most commonly, PGF2α is used for the induction of farrowing and so facilitation of cross fostering. Further, since PGF2α is a smooth muscle stimulant, treatment to stimulate myometrial contractions and uterine evacuation of residual products from parturition or infectious debris, may have beneficial effects on post-weaning fertility. Administration of PGF2α at the moment of insemination has been shown to improve reproductive performances when fertility is otherwise low, such as in sow under summer heat stress.     

Comparison of pregnancy rates with two estrus synchronization protocols in Italian Mediterranean Buffalo cows

The aim in this study was to compare two estrus synchronization protocols in buffaloes. Animals were divided into two groups: Group A (n=111) received 100 microg GnRH on Day 0, 375 microg PGF(2alpha) on Day 7 and 100 microg GnRH on Day 9 (Ovsynch); Group B (n=117) received an intravaginal drug release device (PRID) containing 1.55 g progesterone and a capsule with 10mg estradiol benzoate for 10 days and were treated with a luteolytic dose of PGF(2alpha) and 1000 IU PMSG at the time of PRID withdrawal. Animals were inseminated twice 18 and 42 h after the second injection of GnRH (Group A) and 60 and 84 h after PGF(2alpha) and PMSG injections (Group B). Progesterone (P(4)) concentrations in milk samples collected 12 and 2 days before treatments were used to determine cyclic and non-cyclic buffaloes, and milk P(4) concentrations 10 days after Artificial insemination (AI) were used as an index of a functional corpus luteum. Cows were palpated per rectum at 40 and 90 days after AI to determine pregnancies. All previously non-cyclic animals in Group B had elevated P(4) (>120 pg/ml milk whey) on Day 10 after AI. Accordingly, a greater (P<0.01) relative percentage of animals with elevated P(4) 10 days after AI were observed in Group B (93.2%) than in Group A (81.1%). However, there was no difference in overall pregnancy rates between the two estrus synchronization protocols (Group A, 36.0%; Group B 28.2%). When only animals with elevated P(4) on Day 10 after AI were considered, pregnancy rate was higher (P<0.05) for animals in Group A (44.4%) than Group B (30.3%). The findings indicated that treatment with PRID can induce ovulation in non-cyclic buffalo cows. However, synchronization of estrus with Ovsynch resulted in a higher pregnancy rate compared with synchronization with PRID, particularly in cyclic buffalo.     

Responses of different doses of prostaglandin F(2) alpha on estrus induction, fertility and progesterone levels in subestrous buffaloes

Responses of different doses of PGF(2) alpha (Lutalyse) on estrus induction, fertility, and progesterone levels were studied in buffaloes. Of the total 70 subestrous buffaloes, 71.0 percent (50) exhibited estrus and 44.0 percent (22) conceived to induced estrus with different doses of PGF(2) alpha. Serum progesterone levels were variable before treatment of PGF(2) alpha in subestrous buffaloes and ranged from 0.60 to 4.90 ng/ml. An abrupt decrease in progesterone levels was observed within 24 hours of treatment with 30 mg or 5.0 mg PGF(2) alpha given intramuscularly or by intrauterine fusion, respectively. Serum progesterone levels further decreased and were minimum or similar to those seen in spontaneous estrus (/ 0.5ng/ml) on day 2 to 5 or 6 after PGF(2) alpha treatment. Progesterone patterns further revealed that, in most of the buffaloes, corpora lutea were formed and were functional after the treatment. With 2.5 mg of PGF(2) alpha administered into the uterus, morphological regression of corpus luteum and progesterone were not adequate to induce estrus and ovulation.     

Induction and synchronization of estrus in dogs

Indications for estrus induction in the bitch include missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus and synchronization of ovulation for embryo transfer programs. Reported methods for canine estrus induction include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocryptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide) and exogenous gonadotropins (luteinizing hormone, follicle stimulating hormone, human chorionic gonadotropin, pregnant mare serum gonadotropin, and human menopausal gonadotropin). These methods vary widely in efficacy of inducing estrus, as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction and synchronization in bitches and summarize preliminary results using a long-acting injectable preparation of deslorelin.