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PubMed2006

Time of ovulation and reproductive performance over three parities after treatment of primiparous sows with PG600.

Primiparous sows from a commercial pig farm in central Brazil were utilized to investigate the effect of post-weaning gonadotrophins (given during summer) on estrus, time of ovulation and reproductive performance over three parities. One group of sows (PG600) was treated with a combination of 400 IU equine chorionic gonadotrophin (eCG)+200 IU human chorionic gonadotrophin (hCG) (PG600) 24h after weaning (n=420), whereas the control group received saline (n=408). In a subset of sows (n=150), estrus was detected and time of ovulation was determined by transcutaneous ultrasound. Treatment with PG600 increased the percentage of primiparous sows in estrus within 10 days after weaning (94.8% versus 79.7%) and reduced the first weaning-to-estrus interval (5.3 days versus 8.0 days) relative to control sows (P<0.05). Although the duration of estrus was longer (P<0.05) in sows given PG600 (65.7 h versus 61.0 h), the interval from estrus to ovulation was not different (P>0.05) between PG600 and control sows (46.6 h versus 43.3 h). Treatment with PG600 did not affect (P>0.05) rates of return-to-estrus and farrowing over three parities, but it increased the number of total piglets born (P<0.05) in the second parity (11.2 versus 10.4), thereby minimizing the magnitude of second-litter syndrome. Culling rates from the first to the fourth parity were 26.7 and 24.5% (P>0.05) for PG600 and control sows, respectively. In conclusion, PG600 given 24 h after the first weaning reduced the weaning-to-estrus interval and increased the size of the second litter.

Animals↗

PubMed2003

Role of the sensitivity of detection of oestrus in the submission rate of cows treated to resynchronise oestrus.

OBJECTIVE: To determine if failure to detect oestrus in cows treated to resynchronise oestrus leads to fewer cows being inseminated than are truly in oestrus. PROCEDURE: Cows in three herds were enrolled in a controlled breeding program that involved synchronisation of oestrus for a first round of artificial insemination (AI) followed by resynchronisation for a second round of AI. Just before oestrus was expected at the second round of AI, aids for the detection of oestrus were fitted, which included pedometers, radiotelemetric transmitters (HeatWatch), tail-paint and heatmount detectors. Milk samples were collected at the second round of AI (day 33, herds A and B; day 35, herd C of the treatment program) and were used in combination with pregnancy testing to determine the number of cows that were in oestrus (milk progesterone < 2.0 ng/mL) and cows that were not in oestrus (milk progesterone > 2.0 ng/mL or pregnant at second round of AI) at the time samples were collected. RESULTS: The mean sensitivity of detection of oestrus at the resynchronised oestrus was 92.5% and did not differ significantly between herds (P = 0.19). A total of 75% (60/80) of cows that were retrospectively determined to be not pregnant at the time of the second round of AI were classified as having high (> or = 2.0 ng/mL) concentrations of progesterone in milk at that time. Pregnancy testing of cows about 35 days after AI suggested that early pregnancy loss also contributed to a reduction in submission rates at the resynchronised oestrus. CONCLUSION: Failure to submit cows for insemination at a resynchronised oestrus was mainly due to cows not being in oestrus rather than due to a failure to detect oestrus.

Animals↗

PubMed2002

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.

Animals↗

PubMed2004

Comparison of two estrus synchronization and resynchronization treatments in lactating dairy cows.

Reproductive performance in cows following synchronization of estrus with intravaginal progesterone releasing devices (IVD) has varied with the length of treatment, cyclic status and prolonged return to estrus intervals in some cows following first AI. The objective of this study was to compare two methods of synchronizing and resynchronizing estrus on the reproductive performance of lactating dairy cows. Cows were treated with an IVD (Day 0) for 7 days (n = 350) or 8 days (n = 350), cloprostenol (0.5 mg i.m.) at the time of device removal and estradiol benzoate (EB) at the time of device insertion (1.5mg i.m.), and again 9 days later (1.0 mg i.m.). Cows were also resynchronized starting on Days 23 and 46 by reinsertion of IVDs for either 7 or 8 days and treatment with EB (1mg i.m.) at the time of device insertion and again 9 days later. Cows were inseminated on detection of estrus for 4 days after removal of devices at each of the synchronized estrous cycles. No significant differences in reproductive performance were detected between each treatment throughout the study period. Synchrony of estrus was more precise at the first and second estrus after treatment with an IVD for 8 days compared to 7 days. Cows classified as anestrous had lower reproductive performance than cows classified as cycling and had longer intervals to estrus at the second (P < 0.001) and third estrus (P < 0.06), but not at the first estrus (P = 0.09). Mean time to onset of estrus after IVD removal was less in cows treated with an IVD for 8 days compared to 7 days at each synchronized estrus (P < 0.01). More Holstein-Friesian cows were classified as non-pregnant and not detected in estrus than crossbreed cows (15.7%, 54/343 versus 9.0%, 24/266; [P < 0.05). The results of the study suggested that the main effects of the treatments that were used to synchronize and resynchronize estrus were to alter the timing and synchrony of estrus without affecting fertility.

Administration, Intravaginal↗

PubMed2005

Resynchronization of previously timed-inseminated beef heifers with progestins.

The objective was to determine the efficacy of a previously used CIDR or melengestrol acetate (MGA; 0.5mg/head/day) for resynchronization of estrus in beef heifers not pregnant to timed-AI (TAI). In three experiments and a field trial, heifers were reinseminated 6-12 h after first detection of estrus. Pregnancy diagnosis was done from approximately 25-43 days after either TAI or reinsemination. In Experiment 1, 79 heifers received a once-used CIDR from 13 to 20 days after TAI and 80 heifers were untreated controls. For these two groups, there were 34 and 35 heifers, respectively, not pregnant to TAI; median +/- S.E. intervals from TAI to onset of estrus were 22 +/- 0.2 days versus 20 +/- 0.6 days (P < 0.001); estrus rates were 70.6% versus 85.7% (P = 0.1); conception rates were 62.5% versus 76.7% (P < 0.3); and pregnancy rates were 44.1% versus 65.7% (P = 0.07), for CIDR and untreated (control) groups, respectively. In Experiment 2, heifers (n = 651) were TAI (Day 0) and 13 days later randomly assigned to one of seven groups (n = 93 per group) to receive a once-used CIDR (three groups; Days 13-20), MGA (three groups; Days 13-19), or no treatment (control group). Groups given a CIDR or MGA also received: no further treatment (CIDR or MGA alone); 1.5mg estradiol-17beta (E-17beta) and 50 mg progesterone (P4) in 2 mL canola oil on Day 13; or E-17beta and P4 on Day 13 and 0.5 mg E-17beta on Day 21 (24 h after CIDR removal or 48 h after the last feeding of MGA). Pregnancy rate to TAI was lowest (P < 0.05) for the group given a CIDR plus E-17beta and P4 on Day 13 and E-17beta on Day 21. Variability in return to estrus was greater (P < 0.001) in the control and MGA groups than in CIDR groups. Conception and pregnancy rates in heifers given a CIDR (65.1 and 61.4%) were higher (P<0.01) than those fed MGA (49.6 and 40.4%), but not different from controls (62.2 and 54.9%, respectively). In Experiment 3, 616 heifers received a once- or twice-used CIDR for 7 days, beginning 13+/-1 days after TAI, with or without a concurrent injection of 150 mg of P4 (2 x 2 factorial design). Pregnancy rate to TAI was 47.2%. In heifers that returned to estrus, there was no significant difference between a once- or twice-used CIDR for rates of estrus (68.8%, P < 0.3), conception (65.9%, P < 0.6) and pregnancy (45.3%, P < 0.8). Injecting progesterone at CIDR insertion increased the median interval from CIDR removal to onset of estrus (P < 0.05) and reduced rates of estrus (63.8% versus 73.8%, P<0.05), conception (60.5% versus 70.6%, P = 0.1) and pregnancy (38.6% versus 52.2%, P < 0.02). In a field trial, 983 heifers received a once-used CIDR for 7 days, beginning 13 +/- 1 days after TAI. Pregnancy rate to TAI was 55.2%. The median (and mode) of the interval from CIDR removal to estrus was 2.5 days. Estrus, conception and pregnancy rates were 78.2, 70.3 and 55.0% (overall pregnancy rate to TAI and rebreeding, 78.7%). In summary, a once- or twice-used CIDR for 7 days, starting 13 +/- 1 days after TAI resulted in the majority of nonpregnant heifers detected in estrus over a 4-day interval, with acceptable conception rates; however, injecting progesterone at CIDR insertion significantly reduced both estrus and pregnancy rates, and estradiol treatment after CIDR removal was associated with a decreased pregnancy rate to TAI. Fertility was higher in heifers resynchronized with a once-used CIDR than with MGA.

Animals↗

PubMed2005

Pregnancy rate following GnRH + PGF 2alpha treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment.

Anestrous and lactating Bos taurus by Bos indicus crossbred cows with minimum body condition were studied to determine the efficacy of GnRH+PGF 2alpha combinations for induction of estrus and/or ovulation on pregnancy rate during the months of the year when temperatures are greater. On day 0 (start of treatment), cows were assigned randomly to either treatment or control groups. Treated cows (n = 74) received i.m. 200 microg of GnRH on day 0 and 150 microg of PGF 2alpha 7 days later (day 7). On day 7, treated cows were equally distributed to each of three protocols: (1) Select Synch (n = 25), artificial insemination (AI) 12 h after exhibiting estrus from day 7 (PGF 2alpha injection) until day 12; (2) Ovsynch (n = 24), 200 microg of GnRH at 48 h after PGF 2alpha (day 9) + timed-AI (TAI) 16-20 h later; (3) CO-Synch (n = 25), 200 microg of GnRH + TAI at 48 h after PGF 2alpha (day 9). Control cows (n = 25) received no treatment + AI 12 h after exhibiting estrus from days 0 to 12. Detection of estrus was performed daily during the early morning and evening hours from days 0 to 7 in all the cows, and from days 7 to 12 in the cows treated with Select Synch and in the control group, with the aid of a sterilized bull. Palpation per rectum and transrectal ultrasonography were used on days -30, -20, -10 and 0 to confirm anestrus (absence of CL and no signs of estrus at each evaluation) but with ovarian follicles > or = 10 mm on day 0. Pregnancy rate was 0% for Select Synch, 21% for Ovsynch and 28% for CO-Synch (P < 0.05). In conclusion, the Ovsynch and CO-Synch protocols resulted in greater pregnancy rates compared with the Select Synch protocol in Bos taurus/Bos indicus cows with minimum body condition that were anestrous and lactating during the summer months in a tropical environment.

Anestrus↗

PubMed1986

Indicators of estrus in Holstein cows housed in tie stalls.

Fourteen lactating Holstein cows were observed between 40 and 150 d postpartum to identify physiological and behavioral changes associated with the day of estrus. Ovulation was predicted on 29 occasions from changes in concentrations of progesterone in milk. Estrus was detected by casual observation by the herdsperson 22 times, but only 13 were detected during a daily 30-min exercise period with an androgenized heifer. Morning milk yield and daily feed intake decreased on the day of estrus. Rectal temperature, afternoon milk yield, and number of changes in postural position during the previous night increased on the day of estrus. When an increase greater than one standard deviation from the within-cow mean was considered evidence of estrus, all measures indicated more false positives than true positives. A combination of elevated temperature, increased changes of postural position at night, and depressed feed intake accurately predicted estrus, but only on 6 occasions out of 29.

Animals↗

PubMed2001

Effect of short-term treatment with bovine somatotropin at estrus on conception rate and luteal function of repeat-breeding dairy cows.

We studied the effect of recombinant bovine somatotropin (rbST) at the time of estrus on progesterone concentrations and conception rates of repeat-breeding Holstein cows. We used repeat-breeding cows of varied parity (n = 510). All the animals were clinically healthy and had had at least three unsuccessful services before entering the study. After detection of estrus, the cows were randomly assigned to either a treated (n = 201) or a control (n = 309) group. The animals in the treated group were given rbST (500 mg s.c.) at the time of estrus and again 10 d later. Artificial insemination was performed 12 h after the first detection of estrus. In order to evaluate the effect of rbST on luteal function, blood samples were taken from 10 cows in each group every 3 d for 18 d, starting on the day of insemination (Day 0) to determine progesterone concentrations. Conception rates were significantly higher (P < 0.05) in the cows treated with rbST (29.3%) than in the control cows (16.9%). The effects of rbST were maximal in cows with 8 or more previous unsuccessful services and in cows with 2 to 4 calvings. Progesterone concentrations tended to be higher in nonpregnant cows that were treated with rbST than in those that were not treated. The difference between groups was significant (p < 0.05) on Day 18 after insemination. In pregnant cows there were no significant differences in progesterone concentrations between treated and nontreated animals at any time. Treatment with rbST at estrus improved the conception rate of repeat-breeding Holstein cows. This effect was associated with an increase in circulating progesterone concentrations on Day 18.

Animals↗

PubMed2003

Characteristics of oestrus measured using visual observation and radiotelemetry.

The aim of this study was to measure the level of agreement between characteristics of oestrus measured using visual observation and radiotelemetry. Oestrous cycles in 20 non-lactating Holstein cows were synchronised by treatment with an intravaginal progesterone releasing inserts and injections of oestradiol benzoate for a first oestrus (Round 1) and then re-synchronised for two subsequent and successive oestrous cycles (Rounds 2 and 3). Cows were ovariectomised following the third synchronised oestrus and then retreated to induce oestrus (Round 4). Oestrus was monitored by continuous visual observation and radiotelemetry between 24 and at least 60 h after removal of inserts at Rounds 1-4. Significant differences (P<0.001) were obtained between the mean number of mounts (42.7 versus 17.8), duration of oestrus (14.4h versus 10.9h), total duration of mounts (223.9s versus 33.1s), mean duration per mount (5.6s versus 1.9s), the number of mounts per hour (3.5 versus 2.0) and the interval to oestrus (41.2h versus 42.8h) between values determined by visual observation compared with radiotelemetry, respectively. The 95% limits of agreement for all the characteristics of oestrus measured were wide although the efficiency of detection of oestrus for both methods of recording oestrus were high (97.5% (78/80) versus 93.8% (75/80), for visual observation and radiotelemetry, respectively; P=0.25). We conclude that there is poor agreement between characteristics of oestrus measured with visual observation and radiotelemetry in Holstein cows following monitoring of synchronised oestrous cycles, although both methods were equally efficient for the detection of oestrus.

Animals↗

PubMed2000

Comparison of synchronization of ovulation and induction of estrus as therapeutic strategies for bovine ovarian cysts in the dairy cow.

The benefit of using timed-insemination in lactating dairy cows for the treatment of ovarian cysts lies in the fact that cows do not have to be detected in estrus for insemination and achieving pregnancy. We compared the effectiveness of synchronization of ovulation with timed-insemination and induction of estrus with insemination at estrus in the treatment of bovine ovarian cysts in lactating dairy cows. After Day 65 post partum, a total of 368 lactating dairy cows was divided into 3 groups. Cows in Group 1 (n = 209, normal, noncystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and 100 ug, i.m. GnRH on Day 9 and then were time-inseminated 16 h later. Cows in Group 2 (n = 76, abnormal, cystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and 100 ug, i.m. GnRH on Day 9 and time-inseminated 16 h later. Cows in Group 3 (n = 83, abnormal, cystic) were treated with 100 ug, i.m. GnRH on Day 0; 25 mg, i.m. PGF2 alpha on Day 7; and inseminated at induced estrus within 7 d after treatment with PGF2 alpha. Day 0 was the day of initiation of the study. Conception and pregnancy rates among groups were compared using logistic regression and adjusted for parity, time of year and days in milk. Conception and pregnancy rates of Group 1 cows (31.5%) were not significantly different from those of Group 2 cows (23.6%). However, the pregnancy rate in normal cows (Group 1) was higher (P < 0.01) than in cystic cows (Groups 2 and 3). Cows in Group 3 had a higher conception rate than cows in Group 2 (51.7% > 23.6%; P < 0.01). However, pregnancy rates for cows in Groups 2 (23.6%) and 3 (18%) were not significantly different. The finding indicated that synchronization of ovulation and timed-insemination resulted in pregnancy rates similar to those of synchronization of estrus and insemination at an induced estrus within 7 d for the treatment of ovarian cysts in lactating dairy cows.

Animals↗

PubMed1987

Estrous and litter traits in gilts altered by altrenogest, flushing and pubertal status.

Influences of estrous synchronization with altrenogest and flushing on reproductive traits in gilts were evaluated in three experiments on two farms. Crossbred gilts were fed altrenogest or altrenogest and an additional 1.55 kg ground sorghum grain for at least 10 d before breeding (flushing), or served as controls. Additional grain for the flushing treatment was provided to gilts from the eighth day of altrenogest treatment until they were detected in estrus. The combination of altrenogest and flushing (on Farm A) increased (P less than .05) litter size when compared with gilts treated only with altrenogest and controls that received neither altrenogest nor flushing. This response was entirely among gilts inseminated at their pubertal estrus. For pubertal gilts fed altrenogest and the flushing treatment, litter traits were similar to other treated or control gilts inseminated at a postpubertal estrus. No treatment effects on litter size were detected for gilts inseminated at a postpubertal estrus. Gilts on Farm B responded differently, with larger litter sizes (P = .08) for those treated with altrenogest and flushing plus altrenogest than for control gilts. Reasons for farm differences might be unidentified genetic or management factors or different seasons of the year when gilts were treated on Farm B (summer) vs Farm A (fall, winter and spring). Our results indicate a marked potential for increasing litter size in gilts mated at their pubertal estrus because their unstimulated ovulation rate (no altrenogest or flushing) did not challenge adequately the biological capacity of their uteri.

Animal Nutritional Physiological Phenomena↗

PubMed2004

Effect of the interval between estrus onset and artificial insemination on sex ratio and fertility in cattle: a field study.

We have carried out a field trial in cattle to study the effect of the interval between the onset of estrus and AI on sex ratio and fertility. Data were obtained from 716 cows that had been inseminated at different times between 8 and 44 h from the visual detection of estrus. Before analyzing the data, it was grouped in three intervals considering the time between estrus onset and AI (8-18, 18-30, and > or = 30 h). Our results show that the percentage of calved females (73.05%) is significantly superior for early inseminations (8-18 h), and it decreases 1.85% per hour from the onset of estrus. Delayed AIs (> or = 30 h) produce a significant deviation of the sex ratio towards the males (72.06%); nevertheless, fertility (percentage of successful pregnancies) diminishes significantly, from 66.19% (8-18 h) to 45.35% (> or = 30 h). In conclusion, variations in the interval between the onset of estrus and AI modify sex ratio. However, we must consider its effect on fertility.

Animals↗

PubMed1982

Electronic probe measurements of cervico-vaginal mucus for detection of ovulation in dairy cows: sanitation, clinical observations and microflora.

An electronic vaginal probe with a sanitizing carrier unit has been designed to measure changes in the electrical resistance of cervico-vaginal mucus in the cow. Over 400 cows and heifers have been probed during the period prior to breeding. When 33 heifers and cows were probed 2-3X per day for 30 days, mild irritation of the vaginal mucosa developed during the luteal phase. In all other studies no grossly detectable lesions or other complications resulting from probing were observed either in experimental herds or in farmer herds where breeding tests were conducted. Fertility of probed cows was equal to cows inseminated when estrus was detected visually. Weekly culture of microorganisms from cervico-vaginal mucus collected from three cows probed 3X per week for 22 days resulted in no detectable change in the population of microorganisms. The number of isolates each successive week was 11, 8, 8 and 5, respectively. The sanitary procedures followed appeared to prevent introduction of organisms of any consequence, as judged by the decreasing number of isolates during the probing sequence.

Animals↗

PubMed2003

Comparison of four methods for detection of oestrus in dairy cows with resynchronised oestrous cycles.

OBJECTIVE: To compare the sensitivity and positive predictive value of four methods for detection of oestrus in dairy cows with resynchronised oestrous cycles. PROCEDURE: Oestrous cycles in cows in three herds were synchronised for a first round of artificial insemination (AI) and then resynchronised for a second round of AI. Sensitivity and positive predictive value of four aids (pedometers, radiotelemetric transmitters [HeatWatch; HW], tail-paint and heatmount detectors) that were used to detect the resynchronised oestrus were compared. Milk progesterone concentration and pregnancy testing at 12 weeks were used as the reference standard for cows being in oestrus. RESULTS: The mean sensitivity and positive predictive value for detecting the resynchronised oestrus, for each aid that was used, was > 80%. Tail-paint was significantly more sensitive at detecting oestrus compared to heatmount detectors (P = 0.002), but not significantly more sensitive than pedometers (P = 0.07) or HW (P = 0.55) for detecting oestrus (91.3, 85.7; 81.4 and 88.4%, respectively). Positive predictive value of HW for detecting oestrus was greater than tail-paint (P = 0.014) and heatmount detectors (P = 0.024) but not pedometers (P = 0.25; 100, 91.7, 92.9 and 87.5%, respectively). Positive predictive value of heatmount detectors was greater than pedometers in herd C (93.4% vs 73.3%; P = 0.035) but not in herds A (95.0% vs 90.0%; P = 0.56) or B (90.8% vs 100%; P = 0.10). No other significant differences in sensitivity or positive predictive value of detection of oestrus were found between aids. CONCLUSION: Tail-paint, heatmount detectors, pedometers and HW provide a high sensitivity (> 80%) and positive predictive value (> 85%) of detecting oestrus in dairy cows with resynchronized oestrous cycles.

Animals↗

PubMed1995

Oestrus detection techniques and insemination strategies in Bos indicus heifers synchronised with norgestomet-oestradiol.

Oestrus was synchronised in 57 Bos indicus heifers using norgestomet-oestradiol and pregnant mare serum gonadotrophin. Oestrus was detected by observations made at six-hourly intervals, using oestrogen-treated and chin-ball harnessed steers, heatmount detectors, tail-paint and visual observation. Heifers were inseminated once at either a fixed time of 49.2 +/- 0.4 h (mean +/- SE; n = 29) after implant removal or 12.6 +/- 1.5 h (n = 28) after oestrus was detected. The mean (+/- SE) time to the onset of oestrus was 47.1 +/- 1.9 h, while 90% of heifers recorded in oestrus were detected within 66 h of implant removal. Heatmount detectors were significantly more efficient at detecting oestrus than chin-ball harnessed steers, tail paint or visual observation (P < 0.001). A higher pregnancy rate was obtained in heifers inseminated after oestrus detection compared with heifers inseminated at a fixed-time (57.1 vs 34.5%; P = 0.043) and a higher pregnancy rate was obtained in heifers classified as easy to inseminate compared with heifers classified as difficult to inseminate (57.8 vs 0%, P < 0.001). We conclude that heatmount detectors are an efficient means of detecting oestrus in synchronised B indicus heifers and that pregnancy rates can be increased when insemination follows oestrus detection compared with a fixed-time insemination regimen.

Animals↗

PubMed1992

Synchronization of estrus and fertility in beef cattle with two injections of buserelin and prostaglandin.

Postpartum beef cows and heifers in Group 1 received 8 mug of buserelin on Day 0 (the beginning of the experiment) and 500 microg of cloprostenol (PGF) on Day 6 (GnRH I, n=54). In Group 2 (GnRH II, n=54), the females were injected with buserelin on Day 0 (8 microg) and Day 3 (4 microg), and PGF on Day 6 and Day 9 for females not detected in estrus previously. Animals were bred by AI 12 hours after the onset of estrus. Blood samples were collected on Day -11 and Day 0 to assess cyclicity and on Day 3 and Days 6 to 12 to examine luteal activity. Progesterone levels did not differ between the 2 groups between Days 0 to 9. In both groups, the proportion of spontaneous estruses from Days 0 to 6 was reduced. Precision of estrus was higher (P<0.005) in the GnRH II group than in the GnRH I group of cows that were detected in estrus between Days 6 and 9. The synchronization rate, interval to estrus, pregnancy and conception rates were similar in GnRH I and GnRH II groups. The conception rate and interval to estrus were similar in cyclic and acyclic cows. Increasing the number of buserelin injections enhanced the precision of estrus, but not the conception rate, without any detrimental effect on luteal activity and induced more estruses in postpartum acyclic beef cattle.

Journal Article↗

PubMed1985

Insemination management for a one-injection prostaglandin F(2)alpha synchronization regimen. I. One daily insemination period versus use of the a.m./p.m. rule.

Following detection of estrus in a one-injection prostaglandin F(2)alpha (PGF(2)alpha) synchronization regimen, 261 dairy heifers were randomly inseminated (A.I.) either once between 0800 and 0900 h daily (a.m.) or about 12 h after detection of estrus (a.m./p.m.). During the regimen, 31.8 and 33.3% for the a.m./p.m. and a.m. groups, respectively showed estrus and received A.I. during the pre-PGF(2)alpha period. The remaining heifers were injected with PGF(2)alpha with 95.6% from a.m./p.m. and 96.5% from a.m. showing estrus and receiving A.I. within five days after PGF(2)alpha. Pregnancy rates of 62.9% for a.m./p.m. and 62.0% for a.m. did not differ. Progesterone at the time of injection was similar between groups and was not correlated with either response to PGF(2)alpha or fertility. Percentages of heifers in estrus <24, 25-48, 49-72, 73-96 and >96 after PGF(2)alpha were 4.7, 30.2, 45.6, 14.3 and 5.3, respectively, with a mean time of 61.0+/-1.9 h. Satisfactory conception rate was attained with a.m. insemination.

Journal Article↗

PubMed1990

Milk progesterone profiles in crossbred Brown Swiss x Nellore cattle following natural service.

Ovarian activity and estrous behaviour were monitored through milk progesterone determinations and twice daily visual observations in 70 crossbred Brown Swiss x Nellore cows following natural service. Whole milk samples were collected on the day of estrus (Day 1), Day 11, and every 5 d thereafter until the next estrus or pregnancy confirmation. Seventy percent of the cows behaved as expected, i.e. they showed a 19-to 25-d interval between estrus and the next ovulation, or they became pregnant. Estrous cycles of regular length (18 to 24 d) were found in 54% of the cases. Prolonged luteal phases (interval from estrus to next ovulation > 28 d) were found in 15.7% of cows. Short estrous cycles (interestrous interval < 18 d) were found in 7.1% of the cases. Periods of acyclicity (basal progesterone levels for periods >/= 15 d) were found in 5.8% of the cases, and one cow exhibited estrus while pregnant and had a high progesterone concentration. Cows with a prolonged luteal phase and those with a short estrous cycle had an interval between ovulations of 35.0 +/- 6.7 d (x +/- SD) and 9.6 +/- 3.1 d, respectively. Signs of estrus were not detected in 33.3% of the ovulations confirmed by progesterone determinations. Low conception rates, failures in estrus detection and a high frequency of abnormal postbreeding luteal phases were found.

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