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PubMed1987

Corpus luteum function following spontaneous or prostaglandin-induced estrus in Brahman cows and heifers.

Corpus luteum (CL) function following spontaneous or prostaglandin F2 alpha-induced estrus was studied in 27 Brahman cows and 16 Brahman heifers. Females received one injection of 0, .38, .75 or 2.25 mg alfaprostol (PGF)/100 kg body weight at 12 +/- .1 d post-estrus. Serum progesterone (P4) during CL formation, following the subsequent estrus, increased over time (P less than .001, 1 to 13 d post-estrus) and was influenced by PGF (P less than .06) and a PGF X time interaction (P less than .02). Low serum P4 concentrations were observed during CL formation (d 3, 4, 10, and 12) in cattle that received 2.25 mg PGF. On d 13 post-estrus, CL were removed. No differences in weight, P4 content or number of luteinizing hormone (LH) receptors was evident between CL derived 13 d following spontaneous vs PGF-induced estrus. The CL formed following PGF-induced estrus had fewer large (P less than .002) and small (P less than .09) luteal cells in heifers, a lower (P less than .008) percentage composition of histological type I and II luteal cells in cows and a lower (P less than .0001) in vitro P4 response to LH in both cows and heifers when compared with the CL formed following spontaneous estrus. Cows had heavier (P less than .002) CL with a higher (P less than .05) number of large cells, a higher (P less than .09) percentage composition of histological cell type I and II luteal cells, and a higher (P less than .03) in vitro basal and stimulated P4 secretion. It is concluded that 1) the events associated with artificially shortening the estrous cycle with PGF altered subsequent CL function in Brahman females; 2) cows had heavier CL, which were composed of more steroidogenically functional luteal cells, than heifers and 3) age of animal interacted with PGF to alter subsequent CL function in Brahman females.

Animals↗
PubMed2003

Intravaginal progesterone insert to synchronize return to estrus of previously inseminated dairy cows.

An intravaginal progesterone insert (CIDR insert; 1.38 g of progesterone) was evaluated for synchronization of returns to estrus (SR), conception rate (CR), and pregnancy rate (PR) in dairy cows previously artificially inseminated (AI). Healthy, nonpregnant, lactating Holstein cows, > or = 40 and < or = 150 d postpartum at eight commercial farms were used. Cows detected in estrus and receiving AI 2, 3, or 4 d after one injection of PGF2alpha (25 mg) were assigned as either controls (n = 945), or to receive a CIDR insert (n = 948) for 7 d (14 to 21 +/- 1 d after AI). Cows were observed for returns to estrus from 18 to 26 +/- 1 d after initial AI (resynchrony period) and were reinseminated if in estrus. Vaginal mucus on CIDR inserts (97.3% retention) at removal was scored: 1 = no mucus; 2 = clear; 3 = cloudy; 4 = yellow; and 5 = red or brown. Percentage of cows in estrus (SR) during the 3 d after CIDR insert removal was contrasted to the highest 3-d cumulative percentage in estrus for controls. Cows conceiving to initial AI were omitted in calculations of SR, CR, and PR during resynchrony. Mucous scores of 3 or 4 (mild irritation) were observed in 65% of cows and a score of 5 (more severe irritation) was observed in 2%; otherwise, health was unaffected. The PR to initial AI was lower for cows subsequently receiving CIDR inserts than for controls (32.7 vs. 36.7%). The CIDR insert increased SR (34.1 vs. 19.3% in 3 d) and overall estrus detection (43% in 4 d vs. 36% in 9 d) compared with controls. For the 9-d resynchrony period, CR and PR for CIDR-treated (26.7, 12.2%) and control (30.9, 11.1%) cows did not differ significantly. The CIDR inserts improved synchrony of returns to estrus, slightly reduced PR to initial AI, but did not affect CR or PR to AI during the resynchrony period.

Abortion, Veterinary↗
PubMed1981

Estrus-related odors in cows: time of occurrence.

One Catahoula Leopard Cowdog and three German Shepherd dogs, previously trained to detect odors characteristic of estrus in cows, were used in three experiments to determine when estrus-related odor first appears, how long it persists, and when it disappears in relation to time of estrus. Samples were swabs of reproductive tract fluids taken from vaginas of cycling cows on the day of estrus, at diestrus (8 to 10 days after estrus), and at daily intervals before and after estrus. Estrous odor emerges slowly during the 3 days before estrus, reaches a definite peak in intensity on the day of estrus, and disappears within 1 day thereafter.

Animals↗
PubMed1993

Detection of estrus by radiotelemetric monitoring of vaginal and ear skin temperature and pedometer measurements of activity.

Methods to improve detection of estrus in dairy cows have been studied extensively without wide acceptance of any one method. In the present study, the use of body temperatures and pedometer-monitored activity were evaluated as methods of estrus detection. Twice daily activity levels of 13 lactating cows were monitored using pedometers, and vaginal and ear skin temperature measurements were made continuously using radiotelemetry. Activity increased 2.8-fold at estrus for the 8-h daytime period (0630 to 1430 h), during which cows were given a 5-h turnout period, but not for the 16-h overnight period (1430 to 0630 h), during which cows were confined to tie stalls. When increased activity was used to detect estrus on an individual cow basis, 20 of 25 estruses were detected with 4 false positives. Vaginal temperature increased by .6 +/- .3 degree C at estrus and remained elevated by at least .3 degree C for 6.8 +/- 4.6 h. When increased vaginal temperature was used on an individual basis, 17 of 21 estruses were detected with 3 false positives. Rate of detection of estrus by visual observation was 66%.

Animals↗
PubMed1993

Induction of estrus after thyroidectomy in nonlactating Holstein cows.

Hypothyroidism reportedly decreased sexual behavior in several species. To confirm the role of hypothyroidism in the expression of estrus in cattle, our objective was to determine whether estrus could be induced in ovariectomized cows without intact thyroid glands using estradiol benzoate and progesterone. Eight nonlactating, nonpregnant Holstein cows were thyroidectomized and ovariectomized, and another four cows were ovariectomized only. All cows were given either estradiol benzoate in a crossover design with two replicates during 4 consecutive wk. Cows were observed continuously for estrus from 9 to 45 h after treatment with gonadal steroids. Intensity of estrus was assessed by quantitative measurement of the frequencies of mounting activity and standing behavior. The percentage of cows showing estrus was influenced by thyroidectomy-ovariectomy (78.1%) compared with ovariectomy (31.1%) but was unaffected by hormonal treatment. In contrast, other measures of estrous behavior (duration of standing estrus and frequencies of mounting and standing activities) were unaffected by thyroid status or by hormonal treatments. We concluded that ovariectomized cows without intact thyroid glands exhibit estrus and that the exhibited behavior is similar in intensity and duration to that in ovariectomized cows treated with gonadal steroids. Hypothyroidism may not cause failure to express estrus.

Animals↗
PubMed1992

Synchronization of estrus in dairy goats given norgestomet and estradiol valerate at various stages of the estrous cycle.

Dairy goats were given subcutaneous implants with 3 mg of norgestomet (NOR) and IM injections of 0.625 mg of estradiol valerate and 0.375 mg of norgestomet on day 0 of the estrous cycle (estrus; NOR 0, n = 18), on postestrus day 4 (NOR 4, n = 18), or on postestrus day 11 (NOR 11, n = 15). Ear implants were removed after 9 days. Mean (+/- SE) hours from removal of ear implants to onset of estrus and proportion of goats responding were 36 +/- 3.8 and 83%, 33 +/- 4.0 and 61%, and 36 +/- 2.7 and 93% for groups NOR 0, NOR 4, and NOR 11, respectively. There were no significant differences between treatment groups in time to onset of estrus. The percentage of goats in group NOR 11 that had signs of estrus was significantly greater than the percentage of goats in group NOR 4. Of the goats in groups NOR 0, NOR 4, and NOR 11 that had signs of estrus, 53, 55, and 86%, respectively, had onset of behavioral estrus between 24 and 48 hours after implant removal. All goats that had signs of estrus had onset of behavioral estrus between 12 and 72 hours after implant removal. Mean (+/- SE) hours from removal of ear implants to time of peak concentrations of luteinizing hormone (LH) were 49 +/- 4.1, 49 +/- 3.8, and 49 +/- 4.0 for groups NOR 0, NOR 4, NOR 11, respectively (not different). The percentage of goats in group NOR 11 that had LH peaks was significantly greater than the percentage of goats in group NOR 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Synchronization of estrus in beef heifers with a norgestomet implant and prostaglandin F2alpha.

In a 5-year study (1973-1977), 281 cycling beef heifers were treated with a 7-day norgestomet (SC21009) ear implant and an intramuscular injection of prostaglandin F(2alpha) (PGF(2alpha)) at the time of implant removal or 24 hr before implant removal. Percentages of heifers in estrus by 36, 48, 60, 72, and 120 hr after implant removal were 32.4, 52.7, 71.6, 80.1, and 93.2, respectively. Onset of estrus occurred an average of 49.8 +/- 4.7 hr after treatment. Percentages of heifers in estrus 36 hr after treatment were 5.7 and 51.7 for those with a corpus luteum and those without a corpus luteum (or determined regressing by palpation) at implant removal, respectively. When PGF(2alpha) was injected 24 hr before implant removal, 55% of the heifers were in estrus by 36 hr after implant removal compared to 30% when PGF(2alpha) was injected at the time of implant removal; however, by 60 hr after implant removal the difference was 76% vs. 71%. First-service conception rates for synchronized and nonsynchronized heifers were 62.2% and 59.6%, respectively. During 1976 and 1977 heifers were checked for estrus every 4 hr and inseminated 2, 6, 10, 14, 18, 22, 26, or 30 hr after first detected to be in standing estrus. Conception rate was not significantly affected by time of insemination but tended to be higher for heifers bred 26 and 30 hr after first being detected in standing estrus (78.9% and 70.0% vs. average 59.2%). Treatment with a 7-day norgestomet implant plus a single injection of PGF(2alpha) 24 hr before or at implant removal appears to be a practical technique for synchronizing estrus in cycling heifers without affecting conception.

Journal Article↗
PubMed1986

Time of onset of estrus in gilts.

An experiment was conducted to determine when, during a 24-h period, gilts show the onset of behavioral estrus. Beginning on Day 16 of their first estrous cycle, 42 crossbred gilts were observed at 0600, 1200, 1800, and 2400 h for the onset of their second estrus. Fifty-five percent of the gilts had shown onset of estrus by 0600 h. None of the gilts showed the onset of estrus from 0600 to 1200 h, whereas 24% and 21% of the gilts had shown onset of estrus by 1800 and 2400 h, respectively. Chi-square analysis demonstrated that more (P < 0.025) gilts had shown onset of estrus by 0600 than by 1200, 1800, and 2400 h. When the data were combined for estrous checks by 0600 and 1800 h, 76% of the gilts had their onset of estrus by 0600 h as compared to 24% of the gilts by 1800 h (P < 0.005). In conclusion, more gilts had shown onset of estrus by 0600 h than at any other 6-h period.

Journal Article↗
PubMed1987

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.

Journal Article↗
PubMed1987

Estrus response of indigenous Nigerian Zebu cows after prostaglandin F2 alpha analogue treatment under continuous observations for two seasons.

The study was undertaken to determine the estrus response pattern of Zebu cows indigenous to Nigeria following treatment with prostaglandin F2alpha analogue and to determine the effect of season on the estrus parameters. Eighty cyclic Zebu cows were used in both the dry and wet seasons. Two single intramuscular injections of 25 mg of PGF2alpha analogue were given per cow 11 days apart regardless of the stage of the estrous cycle. The cows were then observed continuously for 168 h following each injection. The proportion of treated cows responding to PGF2alpha treatment in the wet season (90%) was significantly higher (P<0.005) than in the dry season (70.0%). The mean post-injection interval to onset of non-standing estrus (mucus discharge) was 30.6 h and 28.5 h in the dry and wet seasons, respectively. Similarly, the intervals to standing estrus were 69.7 h and 63.9 h in the two seasons, respectively. Seasonal effects were not significant. The duration of non-standing estrus was similar for the two seasons (164.2 h and 162.0 h) while the duration of standing estrus was significantly (P<0.01) longer in the wet season (19.2 h) than in the dry season (12.6 h). Also there was seasonal influence on the body condition score of cows, the palpability of corpora lutea (CL) and the intensity of estrus as determined by the number of mounts (17.9+/-2.0 and 51.2+/-3.4 mounts per cow per estrus period in the dry and wet seasons, respectively).

Journal Article↗
PubMed1987

Ovarian response to human chorionic gonadotropin or gonadotropin releasing hormone in cats in natural or induced estrus.

Human chorionic gonadotropin (hOG) or gonadotropin releasing hormone (GnRH) was given alone or with repeated coital stimuli to study ovarian activity and ovulation in the domestic cat. Adult cats in natural estrus (NE) or treated with follicle stimulating hormone (FSH-P) to induce estrus (2.0 mg/d for 5 d; IE) were assigned to one of five treatments: I, mating (M) only (three times daily for the first 3 d of estrus); II, M + hOG (250 IU, i.m. on Days 2 and 3 of estrus); III M + GnRH (25 mug, i.m. on Days 2 and 3 of estrus); IV, hOG only (250 IU, i.m. on Days 2 and 3 of estrus); or V, GnRH only (25 mug on Day 2 and 3 of estrus). Overall, IE females produced a greater (P < 0.05) number of corpora lutea (7.6 +/- 0.9) and unovulated follicles (18.9 +/- 2.1) than NE cats (4.9 +/- 0.6 and 3.6 +/- 0.9, respectively). For both NE and IE females, the M + hOG treatment (II) produced a greater number (P < 0.05) of ovulations (9.1 and 13.9, respectively) than any other ovulatory regimen (I, 4.1, 6.6; III, 4.1, 7.8; IV, 4.0, 6.2; V, 4.1, 5.6, respectively). These results indicate that 1) the excessive follicle number resulting from FSH-P treatment cannot be reduced with any of the hOG or GnRH treatments tested and 2) the use of hOG with copulatory stimuli synergistically enhances the ovulatory response of cats experiencing a natural estrus or those treated with FSH-P.

Journal Article↗
PubMed1988

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle.

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early (</= Day 11) in the estrous cycle (31.3 +/- 7.4 h) and heifers treated late (> Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early (</= Day 11) in the estrous cycle (20 32 = 62.5% ) compared to cows treated late (> Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).

Journal Article↗
PubMed1993

Estrus and pregnancy rate of dairy cows given one or two doses of prostaglandin F2 alpha 8 or 24 hours apart.

A total of 329 cows was used in 2 experiments to study the effect of PGF2a given 8 or 24 h apart on the number of cows observed in estrus within 7 d and the pregnancy rate to a single insemination at this time. In Experiment 1, 233 cows were divided into 2 groups. Cows in Group 1 (n = 117) were treated twice with 25 mg, im of PGF2a (0 and 8 h) while cows in Group 2 (n = 116) were treated only once (0 h). In Experiment 2, 96 cows were divided into 2 groups. Cows in Group 1 (n = 49) were treated twice with 25 mg, im of PGF2a (0 and 24 h) while cows in Group 2 (n = 47) were treated only once (0 h). In Experiment 1, blood samples were obtained from cows in both groups on Days 0 and 2. However, in Experiment 2, blood samples were obtained from cows in both groups only on Day 0. Plasma progesterone concentration was determined using radioimmunoassay. Cows in both experiments were observed for estrus within 7 d of treatment and were inseminated within 12 h of the observed estrus. In Experiment 1, more cows in Group 1 were observed in estrus within 7 d than in Group 2 (P <0.03). In Experiment 2, there was no significant difference in the number of cows in both groups that were observed in estrus within 7 d. However, the interval from treatment to the first observed estrus for cows not observed in estrus within 7 d was significantly longer in cows treated at 0 and 24 h compared with the cows treated once at 0 h. In both experiments, the pregnancy rate for cows inseminated within 7 d was similar for cows in all groups. From the results of this study, it is concluded that treatment of dairy cows with 2 luteolytic dosages of PGF2a at an 8-h interval resulted in more cows being observed in estrus than at a 24-h interval.

Journal Article↗
PubMed1993

Effect of service on estrus duration in dairy goats.

The objective of this research was to determine the effect of sterile service on estrus duration in multiparous and nulliparous dairy goats. Twenty Nubian goats (10 multiparous and 10 nulliparous) were randomly assigned to of 4 treatment groups (n = 5 animals per group). Group MNS, multiparous without service; Group MS, multiparous with service; Group NNS, nulliparous without service and Group NS, nulliparous with service. Estrus was synchronized by utilization of fluorogestone acetate intravaginal pessaries (40 mg.) over a 12-day period plus 250 IU, i.m. of pregnant mare serum gonadotropin (PMSG) at pessary removal. Estrus was detected with the aid of a vasectomized buck for 5 days after pessary removal for 6-hour intervals (0600, 1200, 1800 and 2400 hours). In the groups that were not serviced the teaser was equipped with an apron and was only allowed to mount. In the serviced groups, the teaser was permitted to mount and service each female on 2 occasions during the first 12 hours of estrus. Estrus initiation for Groups NNS, NS, MNS and MS were (mean +/- SD) 61.5 +/- 29.5, 61.2 +/- 35.4, 63.0 +/- 22.2 and 69.6 +/- 32.5 hours, respectively (P>0.05). Estrus duration for the same groups were (mean +/- SD) 42.0 +/- 12.0, 30.0 +/- 6.0, 42.0 +/- 7.3 and 28.8 +/- 10.7 hours, respectively. These results show that estrus duration was shortened by serving (P<0.01), and that there were no differences between multiparous and nulliparous goats with or without serving (P>0.05). It is concluded that estrus duration in goats is shortened by serving and that no differences in duration exist between multiparous and nulliparous.

Journal Article↗
PubMed1993

Progesterone and estradiol in biodegradable microspheres for control of estrus and ovulation in mares.

Progesterone and estradiol 17-beta in poly (DL-lactide) microspheres were used to control estrus and ovulation in mares after luteolysis was induced by prostaglandin F(2)infinity. Mares were given a single intramuscular injection of biodegradable poly (DL-lactide) microspheres, 1 day following prostaglandin treatment, containing no hormones (control), 0.625 g progesterone and 50 mg estradiol (low dose), 1.25 g progesterone and 100 mg estradiol (medium dose), or 1.875 g progesterone and 150 mg estradiol (high dose; n=15 mares per group). Mares treated with the low dose had significantly longer intervals (P<0.05) to estrus and ovulation than the control mares; however, low dose mares had shorter intervals (P<0.05) to estrus than high dose mares and shorter intervals to ovulation than medium and high dose mares. Regression analysis indicated that the medium dose was sufficient for maximizing interval to ovulation while the high dose maximized interval to estrus. All groups of mares exhibited similar (P>0.05) post-treatment estrus lengths. A clinical response scoring system based on synchrony of both estrus and ovulation within a treatment group was also used to measure the effectiveness of treatments on control of estrus and ovulation. Clinical response scores did not differ (P>0.05) among treatment groups. Mares were randomly assigned for insemination at the beginning of the first post-treatment estrus. Rates for embryo recovery performed by uterine lavage 7 days post-ovulation did not differ (P>0.05) among groups. Concentrations of serum progesterone increased in mares receiving progesterone and estradiol microspheres. At 10 to 14 days post-injection of microspheres, progesterone concentrations were higher (P<0.05) and remained above 1 ng/ml in the mares receiving the high dose. Progesterone concentrations were also higher (P<0.05) on Days -3 to -1 (Day 0 = day of post-treatment ovulation) in mares receiving the high dose when compared to control mares. Gonadotropin concentrations were suppressed (P<0.05) in the medium and high dose groups.

Journal Article↗
PubMed1995

Estrus after treatment with Syncro-Mate B* in ovariectomized heifers is dependent on the injected estradiol valerate.

A series of experiments was conducted to determine why ovariectomized heifers exhibit estrus after they are treated with the estrus synchronization product, Syncro-Mate B(*) (SMB). In Experiment 1, 23 of 40 (58%) ovariectomized heifers exhibited estrus after treatment with SMB. The mean concentration of estradiol-17beta (E(2)) in serum was lower (P < 0.001) before treatment than after implant removal in ovariectomized heifers treated with SMB. Six of 10 heifers from which serum was collected to determine concentrations of LH exhibited estrus and 5 of 6 had a surge of LH in serum after implant removal. In Experiment 2, when no estradiol valerate (EV) was given or when the norgestomet implant period was extended from 9 to 18 d, no heifer exhibited estrus after implant removal. The mean concentration of E(2) for 3 d after implant removal was lower (P < 0.001) in ovariectomized heifers with implants for 18 d versus those with implants for 9 d and was also lower (P < 0.001) in ovariectomized heifers treated only with norgestomet compared with those receiving the standard SMB treatment. When estradiol-17beta was substituted for EV in the SMB treatment, serum E(2) was lower (P < 0.001) after implant removal than in heifers receiving the standard SMB treatment. Experiment 3 demonstrated that combining a norgestomet implant or implant plus a 3-mg injection of norgestomet with EV did not alter concentrations of E(2) in serum on the days when synchronized estrus would be expected following SMB treatment. The results indicate that the SMB-induced estrus in ovariectomized heifers is dependent upon EV in the SMB treatment. Apparently, EV elevates the concentration of E(2) in serum, and the E(2) remains sufficiently high to induce estrus after implant removal.

Journal Article↗
PubMed1994

Endocrine and neural control of estrus in dairy cows.

During proestrus, gonadotropins induce final follicular maturation, resulting in increased secretion of estradiol. Estradiol, in the relative absence of progesterone, acts on the hypothalamus to induce estrous behavior. The mean duration of estrus is 12 to 16 h and ranges from 3 to 28 h. The effects of estradiol appear to be "all or none". That is, once a threshold of estradiol is achieved, estrus is induced, and additional amounts of estradiol above threshold do not further enhance the estrous response (duration and intensity of estrus). Also, progesterone can block the estrus-inducing actions of estradiol. In addition, prior exposure to progesterone does not potentiate the estrus-inducing actions of estradiol except in the early postpartum period. In dairy cows, the first postpartum ovulation is often "silent". In other words, ovulation is not preceded by estrous behavior. High levels of estradiol during late gestation apparently induce a refractory state such that the brain cannot respond to the estrus-inducing actions of estradiol at the first postpartum ovulation. Progesterone can "reset" the brain, allowing it to respond to subsequent estradiol exposure. In the case of the postpartum cow, the corpus luteum formed after the first ovulation provides the progesterone that resets the brain. As a consequence, the second postpartum ovulation is preceded by estrous behavior. Finally, stress (or injection of ACTH) has been shown to delay, shorten, or inhibit completely the expression of estrus in the presence of estrus-inducing concentrations of estradiol.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Fertility following fixed-time AI or insemination at observed estrus in Ovsynch and Heatsynch programs in lactating dairy cows.

The objective of this study was to compare the conception rate for fixed-timed artificial insemination (FTAI) and observed heat artificial insemination (HAI) prior to the scheduled FTAI in Ovsynch and Heatsynch synchronization protocols. In Experiment 1, lactating dairy cows (n=535) received two set-up injections of 25mg prostaglandin F(2alpha) (PGF(2alpha)) i.m., 14 days apart starting at 36+/-3 days in milk (DIM). Cows were blocked by parity and were randomly allocated to either Ovsynch or Heatsynch groups. All cows received 100 microg of GnRH i.m. 14 days after the second set-up injection of PGF(2alpha), followed by a third injection of 25mg PGF(2alpha) i.m., 7 days later. In the Ovsynch group, HAI cows (n=29) were bred on standing estrus after the third PGF(2alpha) before the scheduled second GnRH, whereas FTAI cows (n=218) that were not observed in estrus, received a second injection of 100 microg of GnRH i.m., 48 h after the third PGF(2alpha) and received TAI 8 h after the second GnRH. In the Heatsynch group, all cows (n=288) received 0.5 mg of estradiol cypionate (ECP) 24 h after third PGF(2alpha) and HAI cows (n=172) were bred on standing estrus and FTAI cows (n=116) that were not observed in estrus, received TAI 72 h after the third PGF(2alpha). In Experiment 2, repeat breeder cows (n=186) were randomly assigned to either Ovsynch or Heatsynch groups. The FTAI and HAI cows were inseminated similar to Experiment 1. All cows were observed for estrus three times daily. The associations with the conception rate were modeled with logistic regression separately for Experiments 1 and 2. Of all the variables included in the model in Experiment 1, type of AI (HAI versus FTAI, P=0.0003) and parity (primiparous versus multiparous, P=0.05) influenced the first service conception rate. Over-all conception rate and first service conception rate for HAI cows were higher compared to FTAI cows (33.8% versus 21.3%, and 35.3% versus 21.0%; P=0.001). In the Heatsynch group, cows that received HAI had significantly higher over-all conception rate and first service conception rate compared to FTAI (35.2% versus 17.3% and 36.0% versus 15.5%; P=0.0001). The conception rates in repeat breeder cows for HAI and FTAI (30.1% versus 22.3%) were not different (P>0.1). In conclusion, it was recommended to include AI at observed estrus and fixed-time AI for cows not observed in estrus in order to improve the conception rate in synchronization protocols.

Animals↗