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PubMed2004

Synchronization of estrus in postpartum beef cows and virgin heifers using combinations of melengestrol acetate, GnRH, and PGF2alpha.

The efficacy of various combinations of melengestrol acetate (MGA), GnRH, and PGF2alpha for the synchronization of estrus in Angus-based beef cattle was compared. Hormones were administered as follows: MGA, 0.5 mg x animal(-1) x d(-1) mixed in a grain carrier; GnRH, 100 microg i.m.; PGF2alpha, 25 mg i.m. In Exp. 1, 2, and 3, cows were randomly assigned to treatments by parity and interval postpartum. The detection of estrus and AI were conducted from d -2 until 72 to 96 h after PGF2alpha, at which time cows not detected to be in estrus received GnRH and fixed-time AI (TAI). Data were analyzed separately for primiparous and multiparous cows. In Exp. 1, cows (n = 799) at three locations received GnRH on d -7 and PGF2alpha on d 0 and either no further treatment (GnRH-PGF) or short-term MGA from d -6 through d -1 (STMGA). Among multiparous cows, conception rate at TAI was greater (P < 0.05) for STMGA (41%, 47/115) than for GnRH-PGF treated cows (26%, 24/92). Across herds and parity, synchronized AI pregnancy rate (SPR) was not affected (P > 0.10) by treatment (GnRH-PGF vs. STMGA; 54%, 210/389 vs. 57%, 228/402). In Exp. 2, cows (n = 484) at three locations received either STMGA or long-term MGA from d -32 through d -19, GnRH on d -7, and PGF2alpha on d 0 (LTMGA). Among primiparous cows, SPR was greater (P < 0.01) in LTMGA (65%, 55/85) than STMGA-treated cows (46%, 40/87). Treatment had no effect (P > 0.10) on SPR among multiparous cows (STMGA vs. LTMGA; 59%, 92/155 vs. 64%, 101/157). In Exp. 3, cows (n = 838) at four locations received the LTMGA treatment and either no further treatment or an additional period of MGA exposure from d -6 through d -1 (L&STMGA). Among primiparous cows, SPR tended to be influenced (P < 0.10) by the herd x treatment interaction and was greater (P < 0.01) among L&STMGA (86%, 19/22) than LTMGA-treated cows (56%, 14/25) at a single location. Among multiparous cows, SPR was lower (P < 0.05) in L&STMGA (46%, 165/358) than LTMGA-treated cows (55%, 184/336). In Exp. 4, Angus heifers (n = 155) received either STMGA or 14 d of MGA (d -32 through d -19) and PGF2alpha on d 0 (MGA-PGF). The detection of estrus and AI were conducted from d -2 to d 6. Interval to estrus was greater (P < 0.05) and estrous response was lower (P < 0.05) in STMGA than MGA-PGF-treated heifers. In conclusion, primiparous cows responded more favorably to longer-duration MGA treatments than did multiparous cows. All protocols achieved sufficient SPR to justify their use for improved reproductive management of postpartum beef cows.

Animals↗

PubMed1992

Regulation of estrous cycles in dairy cattle: A review.

Artificial insemination has allowed rapid genetic progress in dairy cattle through the use of semen from genetically superior sires. Detection of estrus and proper timing of insemination remain as major problems limiting reproductive efficiency in dairy herds. Numerous programs for regulating estrous cycles have been examined in this review. While several programs appear promising, results remain variable and the need for accurate detection of estrus has not been eliminated. Nulliparous heifers seem to respond more consistently than lactating cows. Further research is required to develop a successful program that will consistently produce a precise synchrony of estrus and ovulation with normal fertility and be cost effective.

Journal Article↗

PubMed2003

Effects of pre-synchronization using combinations PGF(2alpha) and (or) GnRH on pregnancy rates of Ovsynch- and Cosynch-treated lactating Holstein cows.

In Experiment 1, the effects of two pre-synchronization treatments on synchronized AI pregnancy rates of lactating dairy cattle were compared. Lactating Holstein cows (n=159) received 100 microg of GnRH (im) on day -7 and 25mg of PGF(2alpha) (im) on day 0 and were observed once daily for signs of estrus from day -3 to day 3. Cows detected in standing estrus and those that had lost significant amounts of tail-chalk in the previous 24h were immediately inseminated in a once-daily observation/AI program. Cows not detected in estrus by 72 h after PGF(2alpha) received fixed-time AI (TAI) and a concurrent 100 microg injection of GnRH (im). Cows were randomly assigned by parity and calving date to receive one of the following pre-synchronization treatments: (1) 25mg of PGF(2alpha) (im) on day -35 and day -21 (PGF-PGF) or (2) 100 microg of GnRH (im) on day -14 (GnRH). Fewer (P<0.05) GnRH- (49%, 41/84) than PGF-PGF-pretreated cows (65%, 49/75) were detected in estrus, however, overall pregnancy rates were not affected by pre-synchronization treatment (30 versus 32%, respectively). In Experiment 2, lactating Holstein cows received 100 microg of GnRH (im) on day -7, 25mg of PGF(2alpha) (im) on day 0 and TAI at 60-64 h after PGF(2alpha). Cows were randomized by parity and postpartum interval into pre- and post-synchronization treatments in a 2 x 2 factorial design. Pre-synchronization treatments included: (1) 25mg of PGF(2alpha) (im) on day -35 and on day -21 (PGF-PGF; n=168) or (2) 25mg of PGF(2alpha) (im) on day -21 and 100 microg of GnRH (im) on day -14 (PGF-GnRH; n=180). Within each pre-synchronization treatment, cows were further allocated by parity and postpartum interval to receive as a post-synchronization treatment 100 microg of GnRH (im) at either 48 h (Ovsynch; n=175) or 60-64 h (Cosynch; n=173) after PGF(2alpha). Pregnancy rates at TAI were not affected by pre- (PGF-PGF=26%, 44/168 versus PGF-GnRH=24%, 44/180) or post-synchronization treatments (Ovsynch=29%, 50/175 versus Cosynch=22%, 38/173). However, the numeric shift towards reduced pregnancy rates in Cosynch-treated cows suggests the 12h interval between GnRH and AI may be important to optimize conception rates in GnRH-PGF(2alpha)-based TAI protocols in dairy cattle. In conclusion, each of the pre-synchronization protocols evaluated in present study performed with comparable efficacy. Although the Cosynch protocol facilitates more efficient labor utilization, numeric trends toward reduced conception warrants further investigation.

Animals↗

PubMed1984

Influence of reduced litter size and daily litter separation on fertility of sows at 2 to 5 weeks postpartum.

Two experiments were conducted to determine the influence of various lactational treatments on the incidence of estrus and subsequent fertility of sows. Experiment 1 consisted of 60 crossbred (Yorkshire X Duroc) sows assigned to one of four treatment groups. Litter size was reduced (RLS) to two to four nursing pigs/sow at 2 (n = 16), 3 (n = 15) or 4 (n = 15) wk of lactation for 5 d before final weaning or litters were weaned from control sows (n = 14) at 5 wk of age. Reduced litter size resulted in 19 of 43 (44%) sows detected in estrus on the day of weaning. More (P less than .05) RLS sows were in estrus 0 to 3 d after weaning than control sows. Fertility traits (number of corpora lutea, eggs recovered, egg recovery rate, eggs fertilized, fertilization rate, cleaved eggs and cleavage rate) were similar among treatment groups at 4 to 6 d postestrus. Experiment 2 consisted of 59 crossbred (Yorkshire X Duroc) sows assigned to one of four treatment groups. Litters were separated from their dams for 6 (n = 20) or 12 (n = 10) h/d between 2 and 4 wk or litters were weaned at 2 (n = 13) and 4 (n = 15) wk of age. Lactational estrus was detected in 13 of 20 (65%) sows and 5 of 10 (50%) sows that were separated from their litters for 6 or 12 h/d, respectively. Lactational estrus (LE, n = 18) in sows was observed 4 to 8 d after initial separation, while sows remaining anestrus during lactation (LA, n = 12) were in estrus 2 to 7 d postweaning. Average intervals from separation or weaning to estrus for LE and LA sows and for sows whose litters were weaned at 2 or 4 wk were 5.9, 4.4, 4.4 and 4.2 d, respectively, and were longer (P less than .05) for LE sows. Fertility traits were similar among treatment groups. These studies demonstrate that lactations of 2 to 5 wk and lactational treatments of sows, including either litter reduction before weaning or daily separation of sows from their litters, resulted in similar postweaning or post-treatment intervals to estrus and similar fecundity regardless of treatment or lactation length. While 50% of the sows responded to treatments, reasons for the lack of response in the remaining sows is not explained, but it appears that body weight and backfat of sows at weaning, and feed intake during lactation were unrelated to the success of the treatments imposed.

Animals↗

PubMed2002

The effect of interval from day of administration of bovine somatotropin (bST) to synchronization of ovulation and timed-insemination on conception rate of dairy cows with and without ovarian cysts.

The objective of this study is to evaluate the effect of the interval from the day of administration of bovine somatotropin (bST) to the day of initiation of synchronization of ovulation (Day 0 and 7) and timed-insemination (TAI) on conception rate (CR) of dairy cows with and without ovarian cysts, respectively. Lactating dairy cows (n = 359) were divided into two groups. Cows in Group 1 (n = 238, without ovarian cysts) were treated with 100 microg, i.m. GnRH on Day 0; 25 mg, i.m. PGF2a on Day 8. 100 mirog. i.m. GnRH on Day 10; and inseminated 16 h later without detection of estrus. Cows in Group 2 (n = 121, with ovarian cysts) were treated with 100 microg, i.m. GnRH on Day 0; 100 microg, i.m. GnRH on Day 7; 25 mg, i.m. PGF2alpha on Day 14, 100 ug, i.m. GnRH on Day 16; and inseminated 16 h later without detection of estrus. Between 60 and 63 days postpartum, all cows in the herd were given bST every 14 days for the duration of the study. Logistic regression was used to assess the risk of nonpregnancy associated with interval from bST treatment to Day 0 for cows without ovarian cysts. and both Day 0 and 7 for cows with ovarian cysts adjusting for parity and days in milk. The CR for cows in Group 1 was significantly higher when the interval from last treatment with bST to Day 0 was between 1 and 3 days (28%) compared to 4-6 days (14%). In addition, the risk of nonpregnancy was 2.19 times greater in cows 4-6 days after bST treatment compared to 1-3 days after adjusting for parity and days in milk. The CR for cows in Group 2 was not significantly different when the interval from last treatment with bST to both Day 0 and 7 was between 1 and 3, 4 and 6, and 7 and 14 days. In conclusion, the results of this study suggested bST treatment closer to Day 0 had a positive effect on CR of cows without ovarian cysts, but bST treatment closer to both Day 0 and 7 had no effect on CR of cows with ovarian cysts. This was interpreted to mean that bST had a beneficial effect on either, or both, the preovulatory follicle and the oocyte in dairy cows without ovarian cysts, but not in dairy cows with ovarian cysts.

Animals↗

PubMed1984

Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with syncro-mate B or Norgestomet and Alfaprostol.

Postpartum lactating cows (N=118) and virgin heifers (N=60) were treated with subcutaneous Norgestomet implants for nine days and received either an intramuscular injection (im) of 5 mg estradiol valerate and 3 mg Norgestomet at the time of implant insertion or an im injection of 5 mg Alfaprostol 24 hr before implant removal. Animals were artificially inseminated 12 hr after detection of estrus. Of the cows and heifers, 78% and 88%, respectively, were in estrus within five days after implant removal (P<0.09). There was no difference between treatments in the proportion of animals in estrus or in the timing of estrus (P<0.85). Estrus was detected in a greater (P<0.05) proportion of animals that were cyclic prior to treatment (88%) than among those that were anestrous prior to treatment (77%). Pregnancy rates after five days were similar between heifers that were cyclic (42%) or anestrous (47%) prior to treatment; however, the five-day pregnancy rate in cows that were anestrous prior to treatment was 38% lower than that in cows that were cyclic prior to treatment (17 vs 55%, P<0.01). Although the treatments synchronized or induced estrus in both cyclic and anestrous animals, marked variability in estrous response and fertility among previously cyclic or anestrous postpartum cows limited the effectiveness of the treatments.

Journal Article↗

PubMed2002

Detection of oestrus in Bunaji cows under field conditions.

The objective of this study was to determine the efficacy of some aids for detecting oestrus in 72 Bunaji cows synchronized using two injections of prostaglandin F2 alpha (PGF2 alpha) 13 days apart. Blood samples to determine the accuracy of the aids and ovarian activity by radioimmunoassay technique were collected daily from the day of the second PGF2 alpha injection until oestrus or for 168 hours for 'non-responders'. The aids for detecting oestrus, tail painting, KaMar detectors and a chin-ball mating device (CMD) were applied at the time of the second injection. The oestrus response rate was 73.6% and 61.1%, from the serum progesterone concentration and visual observation, respectively. Based on the total number of oestrus events observed, unaided visual observation, tail painting, KaMar and CMD detected 52.2%, 82.6%, 82.6% and 76.8%, respectively. Visual observation of standing oestrus alone failed to detect 47.8% of the occurrence of oestrus as shown by the concentration of progesterone in the serum and 30.4%, 30.4% and 24.6%, respectively, of the oestrus periods recorded by tail painting, KaMar and CMD. Twenty-eight cows showed abnormalities in progesterone concentration. These investigations showed that oestrus may be detected by using the aids in cows that have been regarded as 'anoestrous' by visual observation of standing heat.

Animals↗

PubMed2001

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

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

Animals↗

PubMed2004

Resynchronizing estrus with progesterone or progesterone plus estrogen in cows of unknown pregnancy status.

Two experiments were conducted to test 2 progesterone (P4)-based treatments that were applied to lactating dairy cattle of unknown pregnancy status to resynchronize estrus of nonpregnant cows. In experiment 1, cows were assigned randomly before a timed AI (TAI) to 1) treatment with a CIDR (controlled internal drug-releasing intravaginal insert containing P4) for 7 d starting on d 13 after TAI (CIDR; n = 300) or 2) no P4 treatment (control; n = 330). Compared with controls, P4 increased the synchrony of those detected in estrus, but failed to increase the overall return rates of non-pregnant cows during the 6 d after CIDR removal (27% vs. 31%; d 20 to 26 after TAI) and did not alter synchronized conception rates (32% vs. 20%) of those inseminated. Use of P4 did not compromise pregnancies resulting from TAI compared with controls (38% vs. 42%), but increased embryo survival between d 29 and 57 after TAI (65.5% vs. 44.3%). In experiment 2, on d 13 after TAI, 196 cows were treated with a CIDR insert for 7 d. Controls received no further treatment. Remaining cows were treated with 1 of 3 estrogen regimens: 1 mg of estradiol benzoate (EB), 0.5 mg of estradiol cypionate (ECP), or 1 mg of ECP on both d 13 and 21. Only 60% of nonpregnant, estrogen-treated cows were detected in estrus between d 20 and 26, and rates of return and conception did not differ among treatments. Estrogen on d 13 did not consistently turn over the dominant follicle when given at CIDR insertion but did increase concentrations of estradiol and reduced luteal function when administered on d 13 and 21 (24 h after CIDR removal). Treatments had no negative effects on milk yield, dry matter intake, or established pregnancies. Use of P4 alone had little effect on overall rates of return to estrus or conception at the first eligible estrus in experiment 1. Combining estrogen with P4 in experiment 2 had no detrimental effects on established pregnancies or subsequent conception and failed to improve return rates beyond P4 alone.

Administration, Intravaginal↗

PubMed1978

Synchronisation of oestrus and pregnancy diagnosis in heifers bred in autumn and winter.

The calving rate to artificial insemination following administration of progesterone or prostaglandin was influenced by ovarian activity at the start of the treatment. Significantly more heifers inseminated on a fixed time basis after a 12-day progesterone treatment calved compared to synchronised or control heifers inseminated at a detected oestrus. Administration of 10 mg oestrogen intravaginally by gelatin capsule attached to the progesterone-containing coil or injection of 5 mg oestrogen and 200 mg progesterone at the start of the 12-day progesterone treatment did not influence the oestrous response of calving rate. The accuracy of detection of non-pregnant heifers by oestrous detection, measurement of progesterone in blood 21 days after AI or rectal examination varied from 90 to 93 per cent. However, both oestrous detection and the progesterone test identified significantly fewer non-pregnant heifers. Rectal examination as a method of diagnosing pregnant heifers was significantly more accurate than either of the above.

Animals↗

PubMed1990

Economic evaluation of pregnancy diagnosis in dairy cattle: a decision analysis approach.

Cost-benefit evaluations of several pregnancy diagnosis schemes were performed. The strategy using on-farm milk progesterone test on d 19 after service, followed by treatment of nonpregnant cows with prostaglandin, was the most profitable returning $10.50 per cow above the cost of the intervention. An increase in efficiency of detection of estrus of greater than 20% among cows diagnosed nonpregnant and an error rate in pregnancy diagnosis of less than or equal to 3% were needed to ensure profitability. Pregnancy diagnosis by uterine palpation per rectum on d 35 after service, combined with the use of pressure-sensitive mounting devices on nonpregnant cows was the second most profitable strategy and returned $5.10 per cow. An increase in efficiency of detection of estrus of greater than or equal to 20% was required to ensure profitability. Embryonic mortality was also critical and an increase from a baseline value of 10% to 12%, as a result of early uterine palpation, made this scheme unprofitable ($-4.80 per cow). Pregnancy diagnosis by uterine palpation per rectum at 50 or 65 d was less profitable, with a return of $2.50 and $.10 per cow, respectively.

Animals↗

PubMed2000

The strategic use of estradiol to enhance fertility and submission rates of progestin-based estrus synchronization programs in dairy herds.

Two experiments were performed to evaluate the efficacy of a progestin-based estrus synchronization program that incorporated the use of estradiol at the initiation of progestin treatment and at 48 h after progestin withdrawal (Exp. 2). In Exp. 1, cyclic, lactating dairy cows (n = 112) were assigned to receive either 1 (1mg) or 2 (2mg) mg of estradiol benzoate via an i.m. injection on d -9 (d 0 = initiation of the breeding season). All cows received an intravaginal progesterone-releasing insert (IPI; CIDR-B) on d -9. On d -2, the IPI was withdrawn and all cows were administered 500 microg of cloprostenol sodium. Beginning on d 0, cows were bred by AI upon detection of estrus. Estrus was observed in similar proportions of cows in each treatment during the first 6 d of AI (90% across treatments), but the interval to estrus was shorter (P < .05) in 1mg (1.26 +/- .18 d) than in 2mg (1.77 +/- .18 d). Conception and pregnancy rates did not vary among treatments; however, cows in estrus on d 0 tended to be less fertile (P = .11) than those in estrus on d 1. In Exp. 2, 408 cyclic cows from three herds were assigned to receive either no synchrony treatment (Control, n = 214) or the treatments described in Exp. 1 (1mg, n = 100; 2mg, n = 94). Anestrous cows from all herds received an IPI from d -9 to -2 (n = 143; Anestrus). All cows in the 1mg, 2mg, and Anestrus groups, with the exception of those detected in estrus between d -1 and 0, also received 1 mg of estradiol benzoate on d 0. Greater than 90% of cows that received an IPI were in estrus between d -1 and 3, and 92.1% of cows in the Control group were in estrus by d 21. Conception rate to first service in 2mg (61.7%) was similar to Control (57.0%), tended to be higher (P = .06) than 1mg (49.0%), and was greater (P < .05) than Anestrus (39.9%). The mean day of conception was earlier (P < .05) in the 2mg (d 13.1 +/- 2.0) than the Control (d 23.2 +/- 1.6) and Anestrus (d 22.4 +/- 1.9) groups. Conception occurred earlier in 1mg (d 17.4 +/- 2.1) than in Control. The proportion of cows that were pregnant at the end of the breeding season tended (P = .09) to be greater in the 2mg and Anestrus groups. This regimen of estrus synchronization improved reproductive competence in cyclic cows and resulted in similar reproductive performance in anestrous cows and untreated cyclic cows inseminated at a spontaneous estrus.

Administration, Intravaginal↗

PubMed2005

Reproductive performance of anestrous dairy cows treated with progesterone and estradiol benzoate.

Anestrus is a major reproduction problem in pasture-based dairy operations that results in poorer reproductive outcomes than herdmates detected in estrus before the start of the seasonal breeding program. The objective of the current study was to assess a combined progesterone and estradiol benzoate treatment program including resynchrony with no treatment. Anestrous pasture-fed dairy cattle (n = 756) in 9 herds were blocked by herd and age and assigned within sequentially presented pairs of cows to be treated with an intravaginal progesterone-releasing insert for 8 d plus 2 mg of estradiol benzoate injected i.m. at insert insertion and 1 mg of estradiol benzoate injected 1 d after insert removal (d -1). Those cows detected in estrus from 0 to 3 d had a used progester-one-releasing insert reinserted for 6 d commencing on d 16 with 0.5 mg of estradiol benzoate injected i.m. 1 d after insert removal (treatment). The other cow within the pair was left as an untreated control (control). Treatment increased the risk of insemination and pregnancy by 28 d into the breeding program and resulted in conception 15 d earlier compared with controls. In contrast, treatment did not increase the risk of pregnancy after 56 d into the breeding program or at the end of the breeding season. It is concluded that treatment of anestrous dairy cattle with progesterone and estradiol benzoate combined with reinsertion of the progesterone insert resulted in earlier conception, but no difference in the final pregnancy rate compared with no treatment.

Analysis of Variance↗

PubMedDate not supplied

Ovarian activity and fertility during the first breeding season of Friesland ewe lambs.

The onset and duration of ovarian activity was assessed in 19 March-born, pure bred Friesland ewe lambs. Blood samples were collected for progesterone assay from 6 August-27 March when the lambs were 5-12 months of age. From 23 January a harnessed vasectomised ram was introduced. Colour marks on the rumps were taken as presumptive evidence of oestrus. During 1-25 March the vasectomised ram was replaced by a harnessed entire ram in order to assess fertility. The mean onset of the first normal luteal cycle, when progesterone levels exceeded 2 ng/ml-1 for two consecutive plasma samples, was on 7 October. The mean age and weight at this time were 29.9 +/- 2.73 weeks and 36.71 +/- 1.39 kg respectively. One ewe lamb became pregnant and lambed on 27 July. The mean date for cessation of ovarian activity (n = 18) was 1 March and the mean number of normal cycles monitored was 8.8 +/- 0.38. Few short luteal cycles were recorded (7/18 lambs) when only transient increases in progesterone levels were detected. The average duration of the breeding season was 142.6 +/- 4.95 days. It is concluded that pure bred Friesland ewe lambs, born during March, will reach puberty around 30 weeks of age and continue regular cyclic activity for approximately 5 months. Entire rams should be joined during January or February to ensure successful matings for lambing and milk production in late summer/early autumn.

Animals↗

PubMed2001

An attempt to detect oestrus from changes in Fourier transform infrared spectra of milk from dairy heifers.

This study was carried out to investigate if there were systematic changes in milk Fourier transform infrared (FT-IR) spectra relative to stage of the oestrous cycle in cattle. Oestrous cycles of 22 lactating heifers were synchronized with two injections of prostaglandin F2alpha (PGF) administered 11 days apart. The heifers were milked twice daily, and milk samples were collected from each heifer at each milking for a period of 70 days, starting on the day of the second PGF injection. Oestrus was diagnosed by visual detection in conjunction with monitoring rectal temperature. Milk samples were analyzed by FT-IR spectroscopy and the spectra data were analyzed using partial least squares (PLS) methods in relation to time of observed oestrus in heifers. In this investigation, it was not possible to identify reliable changes in milk FT-IR spectra in relation to oestrus on a single heifer basis, though there was a weak correlation between FT-IR spectra and expected time of oestrus when the analysis was carried out across all the heifers.

Animals↗

PubMed2005

Effect of artificial insemination on submission rates of lactating dairy cows synchronised and resynchronised with intravaginal progesterone releasing devices and oestradiol benzoate.

This study investigated the hypothesis that a reduction in submission rates at a resynchronised oestrus is not due to the resynchrony treatment involving intravaginal progesterone releasing devices (IVDs) and oestradiol benzoate (ODB) but is associated with artificial insemination (AI) at the first synchronised oestrus. In Experiment 1, cows were synchronised for first oestrus with IVDs, with ODB administered at the time of device insertion (Day 0, 2 mg IM) and 24 h after removal (Day 9, 1 mg IM) and PGF(2alpha) injected at the time of device removal. Cows were then either inseminated (I) for 4 days or not inseminated (NI) following detection of oestrus (first round of AI). Every animal was resynchronised for a second round of AI by reinsertion of IVDs on Day 23 with administration of ODB (1 mg IM) at the time of insertion as well as 24 h after removal (Day 32). Cows detected in oestrus and inseminated for 4 days at the second round of AI were resynchronised for a third round by repeating the resynchrony treatment starting on Day 46 and inseminating cows on detection of oestrus for 4 days. In Experiment 2 the same oestrous synchronisation and resynchronisation treatments were used, but the timing of treatments differed. The cows had their cycles either presynchronised (treatment start Day -23) without AI and then resynchronised, starting on Day 0, for the first round of AI for AI at detected oestrus for 4 days, or they were synchronised (treatment start Day 0) for the first round of AI. In Experiment 1, 91.4% (64/70) and 92.6% (63/68) (P = 0.79) of cows in the I and NI treatments, respectively, were detected in oestrus after the initial synchronisation. At the second round of AI, submission rates for insemination were lower in the I group compared to the NI cows (74.5%, 35/47 versus 92.6%, 63/68, respectively; P = 0.007). Pregnancy rates (proportion treated that were classified as becoming pregnant) in I and NI cows 4 weeks (61.4%, 43/70 versus 63.2%, 43/68) and 7 weeks (77.1%, 54/70 versus 69.1%, 47/68) after the AI start date (AISD) did not differ significantly between treatments. In Experiment 2, presynchronisation and then resynchronisation of oestrous cycles before the first round of AI did not affect oestrous detection rates at the first round of AI (100%, 44/44 versus 98.0%, 50/51; P = 0.54), or pregnancy rates 1 week (63.6%, 28/44 versus 60.8%, 31/51; P = 0.70), 4 weeks (72.7%, 32/44 versus 76.5%, 39/51; P = 0.76) and 7 weeks (81.8%, 36/44 versus 88.2%, 45/51; P = 0.40) after AISD compared to cows that had their cycles synchronised for the first round of AI. These findings support our hypothesis that a reduction in submission rates at a resynchronised oestrus is associated with AI at the first synchronised oestrus and not due to a resynchrony treatment involving IVDs and ODB. This study supports the concept that early embryonic loss following AI at a synchronised oestrus could cause a reduction in submission rates following resynchronisation of oestrus, although investigation of the effect of passing an AI catheter or semen components were not studied per se.

Animals↗

PubMed2001

Effect of oestrous synchronization with estradiol 17beta and progesterone on follicular wave dynamics in dairy heifers.

An experiment was designed to evaluate the effects of estradiol-17beta (E17beta) on follicular wave dynamics and ovulatory response in Holstein heifers receiving either a progestogen ear-implant (Crestar; Intervet International b.v. Boxmeer, The Netherlands) or an intravaginal progesterone-releasing device [controlled internal drug release-bovine device (Eazibreed, CIDR-B; Bodinco BV, Alkmaar, The Netherlands)]. For comparison, another group of heifers was also synchronized using Crestar plus an injection of estradiol valerate (EV) and norgestomet as recommended by the pharmaceutical company. Twenty 20-22-month-old cycling Holstein heifers were allocated to one of the following treatment groups at random stages of the oestrous cycle: (I) simultaneous insertion of Crestar and intramuscular injection of 3 mg norgestomet and 5 mg EV (Crestar 9 + EV 9); (II) simultaneous insertion of Crestar and intramuscular injection of 5 mg E17beta (Crestar 9 + E17beta 9); (III) insertion of Crestar followed 2 days later by intramuscular injection of 5 mg E17beta (Crestar 9 + E17beta 7); or (IV) insertion of CIDR-B device followed 2 days later by intramuscular injection of 5 mg E17beta (CIDR 9 + E17beta 7). The CIDR-B or Crestar implants were removed after 9 days and all heifers received 500 microg Cloprostenol (Estrumate, Pitman-Moore Nederland BV, Houten. The Netherlands). Ovarian ultrasonographic examinations were performed once daily during the synchronization period using a B-mode scanner equipped with a 7.5 MHz linear-array transrectal transducer. In addition, heifers were scanned every 12 h after implant/device withdrawal until 3 days after ovulation in order to monitor follicular activity, detect ovulation and subsequent early luteal formation. Detection of oestrus was performed every 6 h for 4 days after device/implant removal. Oestrus was observed 24-32 h before ovulation in all heifers. The mean hours interval from treatment withdrawal to ovulation was not significantly different (84.0 +/- 16.5, 77.6 +/- 4.1, 73.6 +/- 4.1 and 64.0 +/- 4.4 h for treatments I, II, III and IV, respectively, p > 0.1). However, the variance for heifers treated with EV + norgestomet was significantly larger (Levene's Test; p < 0.01) than those treated with E17beta. All E17beta treatments resulted in dominant follicle suppression and a new wave emerged 4.1 days after treatment compared with 6.6 days for the EV + norgestomet treatment (p < 0.05). The time from emergence of the new ovulatory wave to ovulation was longer for the new wave that emerged after E17beta treatment (9.2 +/- 0.3 days) than after EV + norgestomet treatment (6.9 +/- 0.4 days; p < 0.05). The results of this study suggest that the four treatments used were effective in inducing synchronous behavioural oestrus and ovulation. However, a higher degree of oestrus and ovulation synchrony was observed in heifers treated with E17beta than in heifers treated with EV + norgestomet. Synchronization treatments with exogenous E17beta or EV + norgestomet at the time of progestin device insertion (Crestar or CIDR-B) or 2 days later in heifers can regulate a different emergence pattern of ovarian follicular development in randomly cyclic heifers. The E17beta was effective in inducing follicular suppression and resulted in the consistent emergence of a new follicular wave.

Administration, Intravaginal↗

PubMed1982

Detection of signs of estrus in the charolais cow and its Brahman cross under continuous observation.

In order to study the characteristic signs of an induced estrus in beef cattle maintained in the tropics, 31 animals, 16 pure Charolais and 15 Charolais/Brahman cross, were continuously observed during the first 100 hours following prostaglandin injection. The animals were pastured in a field of approximately 3 hectares. A highly significant relationship (P < 0.01) seemed to exist between behavioural tendencies and the interval following the onset of estrus. Behaviour included butting, attempts to mount, smelling of genitalia (active) and allowing to be mounted and have genitalia smelled (passive). No consistant pattern of sexual activity could be established since some animals were more active than others. Mounts were observed to occur between 6 and 9 in the morning (33%), 9 and 12 at night (16%) and midnight and three in the morning (13%). Differences existed between the Charolais and the Brahman cross with respect to the number of mounts (P < 0.05) and in the response to an induced estrus (P < 0.05). No correlation was found between grazing habits and sexual activity, the former expressed as the number of animals standing up during each hour.

Journal Article↗