Infrared technology for estrus detection and as a predictor of time of ovulation in dairy cows in a pasture-based system

The development and application of an algorithm to assess the ability of an infrared thermography (IRT) device to predict cows in estrus and about to ovulate was investigated. Twenty cows were synchronized using a controlled internal drug release and PGF2α. Vulval and muzzle temperatures were measured every 12 hours from controlled internal drug release insertion to 32 hours after PGF2α treatment and then every 4 hours until ovulation occurred or until 128 hours after PGF2α treatment (whichever occurred first). Thermal images obtained with a FLIR T620 series infrared camera were analyzed using ThermaCAM Researcher Professional 2.9 software. Cows were also monitored for behavioral signs of estrus and color changes of an Estrotect applied to the tail head of each cow 36 hours after PGF2α treatment. Algorithms were developed by adjusting body surface temperature of individual animals for ambient temperature and humidity during each observation period, and were expressed as a deviation from the baseline temperature. Of the 20 cows enrolled in this study, 12 (60%) ovulated. An IRT estrus alert was defined using different thresholds (D = 1 °C, 1.25 °C, and 1.5 °C). Sensitivity and specificity to predict estrus depended upon the chosen threshold level. At a threshold D = 1 °C, the highest sensitivity (92%; n = 11) and the lowest specificity (29%) and positive predictive value (64%) were observed. Conversely, D = 1.5 °C resulted in sensitivity of 75%, specificity of 57%, and positive predictive value of 69%. The mean ± standard deviation intervals between onset and the end of IRT estrus alert to ovulation were 30.7 ± 8.2 and 13.3 ± 7.7 hours, respectively. Ovulation occurred 24 to 47 hours after the onset of the IRT estrus alert for eight out of the 11 ovulated cows (73%). Although the sensitivity of the IRT alert was greater than visual observation (67%) and Estrotect activation (67%), the specificity and positive predictive value were lower than these two aids (i.e., the IRT overpredicted the incidence of ovulation). Results presented indicate that IRT shows some potential as an estrus detection aid; however, further studies investigating the potential to improve the specificity and capturing data throughout entire 21-day reproductive cycles would be worthwhile.     

Antiovulatory effect of a single injection of pure antiestrogen ZK 191703 at early stage of rat estrus cycle

The effects of ZK 191703 (ZK), a pure antiestrogen, on ovulation, follicle development and peripheral hormone levels were investigated in rats with 4-day estrus cycle and gonadotropin-primed immature rats in comparison to tamoxifen (TAM)-treatment. In adult rats, a single s.c. injection of ZK (5 mg/kg) or TAM (5 mg/kg) at an early stage of the estrus cycle (diestrus 9:00) inhibited ovulation, and was associated with suppression of the surge of preovulatory LH, FSH and progesterone. In rats treated with ZK or TAM at a late stage of the estrus cycle (proestrus 9:00), no inhibitory effects on ovulation, the gonadotropin and progesterone surge were detected. ZK treatment at diestrus 9:00, in contrast to TAM, increased the baseline LH level. When immature rats were treated with antiestrogens in the earlier stage of follicular development, 6 and 30 h but not 48 h or later after injection of gonadotropin (PMSG), ovulation was attenuated, associated with a lowered progesterone level. Unruptured preovulatory follicles were found in most of the ovaries from anovulatory animals treated with ZK or TAM. Antiestrogens, ZK and TAM administered at an early phase of the estrus cycle delay the follicular development functionally and inhibit ovulation in rats and suppression of the preovulatory progesterone surge.     

Ovulatory responses and plasma luteinizing hormone concentrations in dairy heifers after treatment with exogenous progesterone and estradiol benzoate

The objectives of this experiment were to determine the effects of 0.5 mg estradiol benzoate, administered intramuscularly 24 h after removal of CIDR-B progesterone containing intravaginal devices, on the time to estrus, ovulation and peak LH concentration in dairy heifers. Ovulatory responses and plasma LH concentrations were examined using 14 Friesian dairy heifers in 2 separate treatment periods. All heifers received a CIDR-B progesterone-containing intravaginal device with an attached 10-mg estradiol benzoate capsule for 12 d. Within each period, 24 h after CIDR-B removal, 7 heifers received an intramuscular injection of 0.5 mg estradiol benzoate while the remaining 7 heifers received an intramuscular injection of a placebo. Blood samples for LH assay were collected at 0, 6 and 12 h, and then every 4 h for 60 h after estradiol injection. Detection of estrus was conducted at 4-h intervals, and ultrasonographical examination to detect ovulation was conducted every 8 h for 88 h after removal of the CIDR-B device. Treatment with estradiol benzoate tended to reduce the time from device removal to the LH peak in Period 1 (median time to LH peak 40.1 vs 63.9 h; P = 6.07). In Period 2, treatment with estradiol had no significant effect on the time to the LH peak, standing estrus or ovulation. We hypothesize that the period effect was due to the stage of cycle at the time of treatment. For heifers treated in Period 1, the stage of cycle was random. However, because of the prior synchronization of estrus, which was implicit in the experimental design, heifers in Period 2 tended to be in late diestrus. The administration of estradiol benzoate after treatment with exogenous progesterone appears to overcome the variability in timing of LH peaks typically occurring in a herd of synchronized heifers due to different stages of follicular development.     

Variations in the vulvar temperature of sows during proestrus and estrus as determined by infrared thermography and its relation to ovulation

The prediction of ovulation time is one of the most important and yet difficult processes in pig production, and it has a considerable impact on the fertility of the herd and litter size. The objective of this study was to assess the vulvar skin temperature of sows during proestrus and estrus using infrared thermography and to establish a possible relationship between the variations in vulvar temperature and ovulation. The experimental group comprised 36 crossbred Large White × Landrace females, of which 6 were gilts and 30 were multiparous sows. Estrus was detected twice daily and the temperature was obtained every 6 hours from the vulvar area and from two control points in the gluteal area (Gluteal skin temperature [GST]). A third variable, vulvar–gluteal temperature (VGT) was obtained from the difference between the vulvar skin temperature and the GST values. The animals were divided into two subgroups: group A consisting of 11 animals with estrus detected at 6:00 AM, Day 4 postweaning, and group B comprising seven animals with estrus detected at 6:00 AM, Day 5 post-weaning. Both groups showed a similar trend in the VGT. The VGT increased during the proestrus, reaching a peak 24 hours before estrus in group A and 48 hours before estrus in group B. The VGT then decreased markedly reaching the lowest value in groups A and B, respectively, 12 and 6 hours after estrus. Although the time of ovulation was only estimated on the basis of a literature review, the matching between the temporal variations of the VGT values and the predicted time of the peak of estradiol secretion that ultimately leads to the ovulation processes suggests that the VGT values represent a potential predictive marker of the ovulatory events.     

Detection of estrous behavior in buffalo heifers by radiotelemetry following PGF2α administration during the early or late luteal phase

This study examined the usefulness of radiotelemetry for estrous detection in buffalo heifers and the impact of prostaglandin F_2α (PGF_2α) administration during the early or late luteal phase on estrous behavior and ovulatory follicle variables. Induction of estrus with PGF_2α at a random stage of the estrous cycle was followed by the arbitrary division of heifers into groups receiving a second dose of PGF_2α during either the early (n = 33) or late (n = 17) luteal phase (6–9 or 11–14 days after estrus, respectively) for the induction of synchronized estrus. The electronic detection of synchronized estrus by radiotelemetry was confirmed using ultrasonography every 6 h until ovulation. Radiotelemetry was 90% efficient and 100% accurate for estrous detection. Intervals between the PGF_2α dose and the beginning of synchronized estrus (40.7 ± 10.9 vs. 56.7 ± 12.8 h) or ovulation (70.0 ± 11.3 vs. 85.6 ± 12.5 h) were shorter (P < 0.05) for heifers receiving PGF_2α during the early luteal phase. PGF_2α administration during the early or late luteal phase produced similar (P > 0.05) results for the duration of estrus, the intervals from the beginning or end of estrus to ovulation, the number and duration of mounts per estrus, the duration of mounts, the diameter of the ovulatory follicle and the luteal profile on day 5 after estrus. In conclusion, radiotelemetry was a suitable tool for the efficient and accurate detection of estrus in buffalo heifers. Treatment with PGF_2α during the early luteal phase had a shorter interval to synchronized estrus and ovulation; however, estrous behavior, ovulatory follicle dynamics and subsequent luteal activity were similar following PGF_2α administration during the early or late luteal phase.     

Hormonal patterns during heat stress following PGF(2)alpha-tham salt induced luteal regression in heifers

Ten, normally cycling, Holstein heifers were assigned to one of two environmental treatment groups (21.3 C, 59% RH or 32.0 C, 67% RH). PGF(2)alpha was used to induce luteal regression and synchronize estrus in order to evaluate temperature effects on various hormonal and physiological responses during the proestrous through metestrous periods. Environmental temperature (32.0 C) evoked a 1.4 C increase in rectal temperature and a 3.6 C increase in skin temperatures. Length of estrus was shorter (P<.10) for heifers at 32.0 C (16 vs 21 hr.). Average plasma progestin concentration between treatments was not different (P>.10). Mean estradiol concentrations were significantly (P<.10) lower in heifers at 32.0 C. No differences (P>.10) were detected in mean concentrations of LH between heifers at 21.3 C and 32.0 C. Preovulatory peak LH concentrations were 32.2 and 33.2 ng/ml plasma, respectively. All animals had a preovulatory surge of LH, suggesting that hyperthermia did not alter factors which regulate hypothalamic control of LH release. Mean basal concentrations of prolactin and corticoids were not different between temperature treatments (P>.10). However, mean corticoid response following ACTH was of lower magnitude, earlier to peak, and of shorter duration in heat stressed heifers. Heat stress did not appear to affect the hormonal milieu in peripheral plasma associated with corpus luteum regression (decrease in progestin) and ovulation (LH surge). However, duration of estrus, concentrations of estradiol at proestrus and corticoid response to injection of ACTH were reduced.     

Effect of timing of artificial insemination on gender ratio in beef cattle

It was recently reported that cows inseminated at approximately 10 or 20 h before an expected ovulation deliver predominately a bull or heifer calf, respectively. The objective of this study was to further investigate the effect of timing of insemination on the gender of offspring in cattle. Angus heifers (n = 41) and cows (n = 98) were used in the study. Heifers were synchronized with a 16-d treatment of melengestrol acetate followed 17 d later with an injection of PGF2alpha. Cows were synchronized with GnRH followed 7 d later with PGF2alpha. A HeatWatch electronic estrus detection system was used to determine the onset of estrus. Based on previous studies, it was assumed that ovulation occurs approximately 32 h after the onset of estrus. Therefore, animals were artificially inseminated at either 8 to 10 h (early; > or = 20 h before expected ovulation) or 20 to 25 h (late; < or = 10 h before expected ovulation) after the onset of estrus. Sixty to 80 d after insemination, ultrasonography was used to confirm pregnancy status and to determine the gender of fetuses. Gender of calves was subsequently confirmed at calving. Data were analyzed for effects of time of insemination and sire or semen batch on gender ratio, as well as any effect of length and/or intensity of estrus on conception rate and gender ratio. Twenty-nine of 41 heifers and 69 of 98 cows were detected in estrus after synchronization and were inseminated; 20 of 29 heifers and 48 of 69 cows were subsequently confirmed pregnant. Neither the length of estrus nor its intensity (number of mounts) had an effect on pregnancy rate or gender ratio (P > or = 0.418). Timing of insemination (early versus late) had no effect on gender ratio (P = 0.887). Semen from 13 sires representing 17 lots was used to inseminate the cows and heifers. No differences (P = 0.494) were detected in the gender ratios resulting from different sires or semen batches. In contrast to previous findings, our results indicate that inseminating beef cattle at approximately 20 or 10 h before an expected ovulation does not alter the gender ratio of the resultant calves.     

The variability in the interval between estrus and ovulation in cattle and its determinants

Fertility of Holstein cows has been decreasing for years and, to a lesser extent, the fertility of heifers too but more recently. A hypothesis to explain this phenomenon may be that the chronology of events leading to ovulation is different for those animals bred nowadays when compared to what was reported previously; this would result in an inappropriate time of insemination. Therefore, two experiments were designed to investigate the relationships among estrus behavior, follicular growth, hormonal events and time of ovulation in Holstein cows and heifers. In the first experiment, the onset of estrus, follicular growth, patterns of estradiol-17beta, progesterone and LH, and the time of ovulation were studied in 12 cyclic Holstein heifers that had their estrus synchronized using the Crestar method; this was done twice, 3 weeks apart. The intervals between estrus and ovulation, estrus and the LH peak, and between the LH peak and ovulation were, respectively, 38.5 h +/-3.0, 9.1 +/- 2.0 and 29.4 h +/-1.5 (mean+/- S.E.M). The variation in the interval between estrus and the LH peak explained 80.6% of the variation in the interval between estrus and ovulation. The intervals between estrus and the LH peak, and estrus and ovulation were correlated with estradiol-17beta peak value (r=-0.423, P <0.04 and r=-0.467, P<0.02, respectively). Positive correlation coefficients for the number of follicle larger than 5 mm, and negative correlation coefficients for the size of the preovulatory follicle with the intervals between estrus and LH peak, LH peak and ovulation, and estrus and ovulation suggest an ovarian control of these intervals. In respect to its role to explain the variation in the interval between estrus and ovulation, the variation in the interval between estrus and the LH peak was evaluated further in a second set of experiments utilizing 12 pubertal Holstein heifers and 35 Holstein cows. The duration of the interval between the beginning of estrus and the LH peak was longer in heifers than in cows (4.15 h versus -1.0 h; P <0.002); the variation for this interval was higher in cows than in heifers (S.E.M.= 1.2 h versus 0.8 h; P=0.01). According to the results of these studies it can be proposed that estradiol and other product(s) of ovarian origin regulate not only the duration of intervals between the onset of estrus and the LH surge but also between the LH surge and ovulation. From the results obtained in the first experiment, it may be postulated that differences observed between cows and heifers for the duration of the interval between onset of estrus and the LH surge as well as for the variation of this interval would be observed also for the interval between the onset of estrus and ovulation. Therefore, on a practical point of view, the long interval between the onset of estrus and ovulation and the high variation of this interval, especially in cows, may be a source of low fertility and should be considered when analysing reproductive disorders.     

Limited multiple ovulation in heifers fed high plane of nutrition before PMSG stimulation and steroid hormone concentrations in single, twin and multiple ovulators

Limited multiple ovulation (2-4 CL's) in heifers was attempted by feeding a low or a high plane of nutrition during an estrous cycle and injecting a low dose of PMSG at day 16 of that cycle. Multiple ovulation was achieved in 52% of the 19 dairy x beef crossbred heifers that received 1200 I.U. of PMSG. The ratio of the number of heifers which ovulated between 2-4 follicles to those ovulating 1 and more than 4 was higher (P<0.05) in heifers which were fed a high plane of nutrition than in those which were fed a low plane of nutrition. Thirty-six hours after the PMSG injection and prior to estrus, the concentration of E(2)-17beta was less in heifers with 1 growing follicle developing into 1 CL than in heifers with 2 or >2 growing follicles developing into CL's (P<0.01). Heifers with >2 growing follicles developing into CL's had more E(2)-17beta than those which eventually formed 2 CL's (P<0.01). Moreover, in heifers with >2 CL, E(2)-17beta concentration increased regularly until at least 96 hrs after the PMSG injection, while in heifers with 1 CL or 2 CL's, the concentration plateaued at 60 hrs after the PMSG injection. Progesterone concentration during proestrus was lower in heifers that developed >2 CL's than in those with 1 or 2 CL's (P<0.05).     

Synchronization of Oestrus in Heifers with Norethisterone

Sixty-five heifers in different stages of the oestrus cycle were fed norethisterone once daily for 17 days at doses of 0.2, 0.6 and 1.0 mg/kg body weight. During treatment swollen vulva, mucus discharge, open and reddened portio and udder enlargement were noted. Norethisterone was effective in suppressing oestrus and ovulation at doses of 0.6 and 1.0 mg/kg. Extremely good heat-synchronization followed the treatment and 98 % of the heifers came on heat within a two-day period. Fifty-five % conceived after the first insemination. In the group receiving 0.2 mg norethisterone per kg, three out of 13 heifers showed psychic heat during treatment. Poor heat synchronization and low conception rate were obtained in this group. A possible effect of cycle stage on heat synchronization was noted only in the 0.2 mg group where a better result was obtained when treatment began in the follicular phase.     

Reproductive characteristics of cyclic beef heifers treated with the prostaglandin analog luprostiol

One hundred and twenty crossbred Angus heifers, after exhibiting a 17- to 23-d estrous cycle, were placed into six groups of 20 heifers each and administered 2 ml i.m. propylene glycol containing either 0 (controls), 3.75, 7.5, 15.0 or 30.0 mg of luprostiol, or saline containing 0.5 mg cloprostenol (Groups 1 through 6, respectively). Heifers were observed for estrus every 6 h and all treatments were given 6.5 to 8.0 d after heifers were observed in standing estrus. Blood samples were collected after treatments from 10 heifers in each groups. Blood serum was assayed for progesterone. The synchronization period was considered to be 120 h after administration of luprostiol or cloprostenol. There were 0, 16, 17, 18, 20 and 18 heifers observed in estrus during the synchronization period in Groups 1 through 6, respectively. Progesterone concentrations in blood serum dropped below 1 ng/ml in 0, 8, 9, 10, 10 and 10 of the heifers from which blood samples had been taken in the six groups. All heifers observed in estrus were artificially inseminated. During the synchronization period, 0, 12, 14, 15, 16 and 10 heifers conceived in Groups 1 through 6, respectively. The interval from injection to estrus for the 89 heifers that exhibited estrus in the synchronization period averaged 49.0 h and was not different among the luprostiol and cloprostenol treated groups. Control heifers returned to estrus an average of 13.2 d after the treatment. The number of heifers that conceived at first insemination, regardless of when estrus occurred, was 16, 15, 16, 16, 16 and 12, and the total number that conceived at the first and second inseminations was 18, 18, 17, 19, 19 and 16 for Groups 1 through 6, respectively. Based on serum progesterone concentration and/or interval from treatment to estrus, 15 and 30 mg of luprostiol effectively regressed corpora lutea (100%) when administered between 6.5 and 8.0 d after estrus, and the estrous response and conception rate for these two groups equalled or exceeded that of the control and cloprostenol groups.     

Effects of dose and route of administration of cloprostenol on luteolysis,estrus and ovulation in beef heifers

Four experiments were conducted (with crossbred beef heifers) to determine the effects of dose and route of administration of cloprostenol on luteolysis, estrus and ovulation. In Experiment 1, 19 heifers with a CL > or = 17 mm in diameter were randomly allocated to receive cloprostenol as follows: 100 microg s.c., 250 microg s.c., or 500 microg i.m. Heifers given 100 microg s.c. had a longer (P<0.03) interval (120.0 h+/-10.7 h; mean+/-S.E.M.) from treatment to ovulation than those given either 250 microg s.c. or 500 microg i.m. (92.0 h+/-7.4 h and 84.0 h+/-8.2 h, respectively). In Experiment 2, 28 heifers were given porcine LH (pLH), followed in 7 days by cloprostenol (same doses and routes as in Experiment 1), and a second dose of pLH 48 h after cloprostenol. Luteolysis occurred in all heifers, and no difference was detected among treatment groups in the interval from cloprostenol treatment to ovulation (mean, 101 h; P<0.9). In Experiment 3, 38 heifers at random stages of the estrous cycle (but with plasma progesterone concentrations > or =1.0 ng/ml) received 500 or 125 microg cloprostenol by either i.m. or s.c. injection (2/2 factorial design). There was no difference (P<0.4) among groups in the proportions of heifers that were detected in estrus or that ovulated. However, the interval from cloprostenol treatment to estrus was shorter (P<0.02) in the group that received 500 microg i.m. (58.5h) than in the other three groups (500 microg s.c., 75.0 h; 125 microg i.m., 78.0 h; and 125 microg s.c., 82.3h). In Experiment 4, 36 heifers were treated (as in Experiment 3) on Day 7 after ovulation. The proportions of heifers detected in estrus and ovulating after 125 microg s.c. (33 and 44%, respectively) or 125 microg i.m. (55 and 55%) were lower (P<0.05) than in those that received 500 microg s.c. (100 and 100%), but not different from those receiving 500 microg i.m. (78 and 89%, respectively). Overall, ovulation was detected in 9/18 heifers given 125 microg and 17/18 heifers given 500 microg of cloprostenol, on Day 7 (P<0.01) and was detected in 17/20 heifers given 125 microg and 18/18 heifers given 500 microg of cloprostenol, at random stages of the estrous cycle (P>0.05). Although there was no significant difference in luteolytic efficacy between i.m. and s.c. injections of the recommended dose (500 microg) of cloprostenol, variability in responsiveness to a reduced dose depended upon CL sensitivity, therefore, reduced doses cannot be recommended for routine use.     

Effect of estrus synchronization with Syncro-Mate-B((R)) on serum luteinizing hormone, progesterone and conception rate in Brahman heifers

Twenty-two estrous cyclic, 2-yr-old Brahman heifers were randomly assigned to receive either estrus synchronization with Syncro-Mate-B((R)) (SMB; 11) or no treatment (Control; 11). Blood samples were collected via tail vessel puncture at onset of estrus and daily thereafter until Day 11 after estrus. Blood samples were also collected from five SMB and five Control heifers at 0, 4, 8 and 12 h after the onset of estrus. All samples were processed to yield serum and stored at -20 degrees C until radioimmunoassay. Heifers were inseminated by one technician using semen from a single ejaculate of a Brahman bull 12 h after the onset of estrus. All SMB heifers exhibited estrus within 72 h of implant removal. All heifers had corpora lutea (CL) detected by rectal examination 8 to 12 d following estrus. Serum luteinizing hormone (LH) was not affected by treatment, time (4 - h intervals) or an interaction of treatment by time (P > 0.10). Independent analysis with h indicated that at h 12, SMB (2.2 +/- 0.06 ng/ml) had lower LH than did control heifers (8.9 +/- 2.1 ng/ml). Serum progesterone increased from Day 1 through Day 12 in all heifers, which is indicative of functional CL. Serum progesterone was affected by treatment (P < 0.0001) and time (d intervals; P < 0.10). Progesterone elevation was lower (P < 0.05) and area under the progesterone curve was lower (P < 0.03) in SMB (5.6 +/- 0.5 ng/ml, 32.0 +/- 4.5 units, respectively) when compared with control heifers (7.0 +/- 4 ng/ml, 43.7 +/- 2.4 units, respectively). Conception rate was lower (P < 0.01) in SMB heifers (2 of 11) than in control heifers (8 of 11). The lowered conception rate in SMB treated Brahman heifers may be due to altered timing of LH release following estrus, resulting in an altered time of ovulation.     

Timing of the onset and duration of ovulation in superovulated beef heifers

Thirty-two beef heifers were induced to superovulate by the administration of follicle stimulating hormone-porcine (FSH-P). All heifers received 32 mg FSH-P (total dose) which was injected twice daily in decreasing amounts for 4 d commencing on Days 8 to 10 of the estrous cycle. Cloprostenol was administered at 60 and 72 h after the first injection of FSH-P. Heifers were observed for estrus every 6 h and were slaughtered at known times between 48 to 100 h after the first cloprostenol treatment. The populations of ovulated and nonovulated follicles in the ovaries were quantified immediately after slaughter. Blood samples were taken at 2-h intervals from six heifers from 24 h after cloprostenol treatment until slaughter and the plasma was assayed for luteinizing hormone (LH) concentrations. The interval from cloprostenol injection to the onset of estrus was 41.3 +/- 1.25 h (n = 20). The interval from cloprostenol injection to the preovulatory peak of LH was 43.3 +/- 1.69 h (n = 6). No ovulations were observed in animals slaughtered prior to 64.5 h after cloprostenol (n = 12). After 64.5 h, ovulation had commenced in all animals except in one animal slaughtered at 65.5 h. The ovulation rate varied from 4 to 50 ovulations. Approximately 80% of large follicles (> 10 mm diameter) had ovulated within 12 h of the onset of ovulation. Onset of ovulation was followed by a dramatic decrease in the number of large follicles (> 10 mm) and an increase in the number of small follicles (相似文献   

Sexual characteristics of female dogs during successive phases of the ovarian cycle

Five female beagles were examined periodically throughout their second biannual cycle of proestrus, estrus, metestrus, and anestrus for fluctuations in several physiological and behavioral charateristics. Physiological measures included plasma levels of estradiol and progesterone as well as the vulvar swelling and vaginal bleeding that begin with proestrus and continue in estrus. Behavioral tests revealed changes in female receptivity, attractivity, and proceptivity. Estradiol increased prior to the onset of proestrus and declined during estrus. Progesterone levels were low during most of proestrus, increased from the beginning to the end of estrus, and remained elevated during the first month or more of metestrus. While they were in proestrous females were not receptive but they and their vaginal secretions were highly attractive to males. Attractivity remained high throughout estrus and declined abruptly in the next 24 hr. Receptivity increased over the first 3 days of estrus and continued at a high level until the last 3 days during which it decreased slightly, and then dropped nearly to zero within the next 24 hr. “Sexual reflexes” of the vulva, tail, and hindquarters followed the same course of changes described for attractivity. Proceptive behavior, including seeking proximity to caged males and display of solicitation responses during mating tests was characteristic of females during proestrus and estrus but uncommon or absent in other phases of the cycle. It is hypothesized that in the natural cycle, attractivity and proceptivity develop during proestrus as a consequence of rapidly increasing secretion of estrogen. The onset of receptivity is due to synergistic action of estrogen and progesterone. Estrogen secreted during proestrus primes the system, and progesterone secreted just before and during estrus activates it. Termination of receptivity is thought to be due to the marked decline in estrogen, to inhibition by high concentrations of progesterone, or to a combination of these factors.     

Comparison of controlled internal drug release device and melengesterol acetate as progestin sources in an estrous synchronization protocol for beef heifers

The objectives of this experiment were to compare estrous synchronization responses and AI pregnancy rates of beef heifers using protocols that included either CIDR or MGA as the progestin source. The hypotheses tested were that: (1) estrous synchronization responses after (a) progestin removal, and (b) PGF(2alpha); and, (2) AI pregnancy rates, do not differ between heifers synchronized with either progestin source. At the start of the experiment (Day 0) in both years, heifers were assigned randomly to receive, MGA supplement for 14 days (MGA-treated; n=79) or CIDR for 14 days (CIDR-treated; n=77). On Day 14 progestin was removed and heifers were observed for estrus up to and after PGF(2alpha) on Days 31 and 33 for CIDR-treated and MGA-treated heifers, respectively. Heifers that exhibited estrus within 60h after PGF(2alpha) were inseminated by AI 12h later; the remaining heifers were inseminated at 72h after PGF(2alpha) and given GnRH (100mug). More (P<0.05) CIDR-treated heifers exhibited estrus within 120h after progestin removal than MGA-treated heifers. Intervals to estrus after progestin removal were shorter (P<0.05) for CIDR-treated heifers than MGA-treated heifers. More (P<0.05) CIDR-treated heifers exhibited estrus and were inseminated within 60h after PGF(2alpha) than MGA-treated heifers. Pregnancy rates did not differ (P>0.10) between MGA-treated (66%) and CIDR-treated (62%) heifers. In conclusion, the use of CIDR as a progestin source in a 14-day progestin, PGF(2alpha), and timed AI and GnRH estrous synchronization protocol was as effective as the use of MGA to synchronize estrus and generate AI pregnancies in beef heifers.     

Evaluation of short estrus synchronization methods in dairy cows

In the present study, two new short estrus synchronization methods have been developed for lactating dairy cows. The study was completed in three consecutive phases. In experiment (Exp) 1, 32 cows, that were not detected in estrus since calving between the 50th and 84th post-partum days, were treated with PGF2alpha (PGF, d-cloprostenol, 0.150 mg), estradiol propionate (EP, 2mg) and GnRH (lecirelina, 50 microg) at 24h intervals, respectively, and timed artificial insemination (TAI) was performed 48 h after PGF. Different from Exp 1, EP and GnRH were given at 48 and 60 h, respectively after PGF in Exp 2 (n=20), instead of 24 and 48 h. Ovulations were investigated by ultrasound for 7 days starting from the day of PGF treatment, and ovulation rates were compared with the ones obtained in Exp 1. In Exp 3, cows were given the same treatments as Exp 2, but treatments started at certain estrus stages. Cows detected in estrus and with a confirmed ovulation (n=27) after the second PGF given 11 days apart were assigned to three treatment groups. Treatment was initiated at Day 3 (group metestrus, n=9), Day 12 (group diestrus, n=9) and Day 18 (group proestrus, n=9) after ovulation. All cows included in Exp 3 were TAI between 16 and 20 h after GnRH treatment. In Exp 2 and 3, blood samples were obtained once every 2 days, starting from Day 0 to the 10th day after GnRH injection, and once every 4 days between the 10th and the 22nd days after GnRH to examine post-treatment luteal development. During the study, animals exhibiting natural estrus were inseminated and served as controls (n=85). The rate of estrus was found to be significantly higher in cows with an active corpus luteum (CL) at the start of Exp 1 (72.7% vs. 30.0%, P<0.05) and the pregnancy rate tended to be higher than cows without an active CL (40.9% vs. 10.0%, P=0.08). Compared to those in Exp 1, cows in Exp 2 had higher rates of synchronized ovulation (94.1% vs. 59.1%, P=0.013). In Exp 3, estrus (P<0.001) and pregnancy rates (P=0.01) were found to be significantly higher in cows in the proestrus group than in those in the metestrus group. Comparable pregnancy rates were obtained from the first and second inseminations in Exp 1 and 3 with results from those inseminated at natural estrus (P>0.05). It was concluded from the study that the treatment in Exp 1 and 3 could result in comparable pregnancy rates after timed AI of lactating dairy cows at random stages of the estrus cycle relating to those inseminated at natural estrus, but the stage of the estrus cycle can have significant effects on pregnancy rates.     

Ovarian function in crossbred beef heifers treated with dexamethasone

Each of 32 crossbred beef heifers was brought from pasture on day 16 of its estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field Dexamethasone (FD), Pen Control (PC), and Pen Dexamethasone (PD). Field groups were kept in a 0.8-ha field and pen groups were kept in 4.6-x 9.8-m pens in a pole barn during the trial. Dexamethasone (DEX) groups received 20 mg of DEX on cycle day 16 and 30 mg daily on days 17 through 20. Control heifers received an equal volume of physiological saline solution on corresponding cycle days. Average treatment cycle lengths (±SD) for control heifers in FC and PC groups were 21.1 ± 2.8 and 21.6 ± 1.8 days, respectively, and were not significantly different. Average time from progesterone decline (<1 ng/ml) to estrus was two days for each of the control groups. Four DEX-injected heifers had not shown estrus by day 44 of the treatment cycle. Progesterone had declined for two of these heifers by cycle day 18 and remained below 1 ng/ml past cycle day 48. The other two showed a decline in plasma progesterone by cycle days 18 and 32, respectively, and a progesterone rise by day 42 without having been detected in estrus. The remaining 12 DEX heifers had an average cycle length of 29.4 days. Four extended cycles resulted from extended CL function, five from an extended period from progesterone decline to estrus and three from a combination of these factors. These observations suggest that the administration of pharmacological doses of glucocorticoid during the late diestrus or early proestrus may result in altered ovarian function.     

The effect of estradiol benzoate administration on estrous response and synchronized pregnancy rate in dairy heifers after treatment with exogenous progesterone

The objectives of this trial were to determine the effects of 0.5 mg estradiol benzoate administered intramuscularly 24 h after the removal of progesterone-containing intravaginal devices on the occurrence and timing of estrus, synchronized pregnancy rate and synchronized conception rate in dairy heifers. A clinical trial was conducted involving 750 dairy heifers in 13 herds. Within each herd heifers were randomly allocated to 1 of 2 estrus synchronization treatments. All heifers received a CIDR-B progesterone-containing intravaginal device containing a 10 mg estradiol benzoate capsule for 12 d. Twenty-four hours after CIDR-B removal one group received 0.5 mg, im estradiol benzoate while the other group received an intramuscular injection of a placebo. Estrus detection was performed at 48 and 72 h after intravaginal device removal, and heifers detected in estrus at those times were inseminated. Administration of estradiol benzoate 24 h after removal of CIDR-B devices significantly increased the number of heifers exhibiting estrus within the observation period (96.1 vs 90.5%; P < 0.01). It also altered the onset of estrus so that significantly more heifers were in estrus (86.6 vs 72.3%; P < 0.01) and conceived (47.1 vs 37.5%; P < 0.05) by 48 h after CIDR-B device removal. The synchronized conception rate was unaffected by treatment. The distribution of estrus was such that fixed-time insemination after estrus synchronization with this treatment program may be recommended.     

The effects of exclusion of progesterone or Day 0 GnRH from a GnRH,prostaglandin, GnRH + progesterone program on synchronization of ovulation in pasture-based dairy heifers

This study evaluated the effect of removing the GnRH injection on Day 0 or the progesterone (P4) device from a GnRH, PGF2α, GnRH (GPG) + P4 program on follicular dynamics and synchronization of ovulation in dairy heifers. Friesian and Friesian × Jersey heifers, in autumn 2009 (n = 35) and spring 2010 (n = 38), were randomly allocated to one of three estrus synchronization programs. The first group (GPG + P4) received 100 μg GnRH on Day 0, a P4-releasing intravaginal device from Days 0 to 7, 500 μg PGF2α on Day 7, and 100 μg GnRH on Day 9, followed by fixed-time artificial insemination 16 to 20 hours later. The program for group 2 (GPG) was the same as group 1 with the exclusion of the P4 device. Group 3 (P + G + P4) was treated the same as group 1, except for the absence of the GnRH treatment on Day 0. Ultrasonography was performed on Days 0, 1, 2, 3, and 7 and then at 12 hourly intervals on Days 9 to 11. Dominant follicle size was affected by both treatment and day, and there was also a significant interaction (P < 0.02) between treatment and day. Mean dominant follicle size was larger in the heifers treated with P + G + P4 on Days 1 to 3 than those treated with GPG + P4 (P < 0.02) and, on Day 2, than those treated with GPG (P = 0.005). However, on Day 7, mean dominant follicle size was larger in heifers treated with GPG than heifers treated with P + G + P4 (P = 0.03). The emergence of a new follicular wave was later in heifers treated with P + G + P4 than heifers, which received a GnRH injection on Day 0 (4.3 ± 0.7 days, compared with combined GPG + P4 and GPG 3.0 ± 0.3 days; P = 0.03). The proportion of heifers that ovulated within the first 48 hours after the Day 9 injection of GnRH was not affected by treatment (GPG, 81%; GPG + P4, 84%; and P + G + P4, 100% [including early ovulation]; P = 0.11). The timing of the ovulation was not different between treatments (P = 0.97).