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

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

Effectiveness of administration of gonadotropin-releasing hormone at Days 11, 14 or 15 after anticipated ovulation for increasing fertility of lactating dairy cows and non-lactating heifers

One strategy for improving fertility in cattle is mid-cycle administration of GnRH to increase progesterone secretion and delay luteolysis. This strategy might be especially useful during hot weather because heat stress increases uterine prostaglandin release and reduces development of the elongating embryo. A series of experiments was conducted to test the efficacy of GnRH for increasing fertility. There was no effect of administration of 100 microg GnRH at Day 11 after anticipated ovulation on pregnancy rates in virgin heifers subjected to timed artificial insemination (TAI) during the summer. Similarly, there was no beneficial effect of administration of GnRH at Day 11 after anticipated ovulation on pregnancy rates of lactating cows subjected to TAI in summer and winter. Three experiments tested effects of injection of GnRH at Days 14 or 15 after anticipated ovulation on pregnancy rates of lactating cows. The first experiment used 477 lactating cows subjected to TAI. Cows receiving GnRH at Day 14 had higher pregnancy rates in both summer and winter than cows receiving vehicle (20.3 versus 12.7%, P<0.02). When this experiment was repeated during summer with 137 cows, there was a negative effect of GnRH treatment at Day 14 on pregnancy rate. In the third experiment, lactating cows during summer were inseminated at detected estrus and cows were assigned to treatment with either GnRH or vehicle at Days 14 or 15 after insemination. Pregnancy rates were 25.6% (32/125) for cows receiving vehicle, 20.7% (19/92) for cows receiving GnRH at Day 14, and 20.3% (16/79) for cows receiving GnRH at Day 15. In conclusion, GnRH administration at Days 11-15 after anticipated ovulation or estrus did not consistently increase pregnancy rates in either cool or warm seasons.     

Pregnancy rate in peripuberal beef heifers following treatment with syncro-mate-B and gonadotropin releasing-hormone

A study was conducted to evaluate the effectiveness of treatment with Syncro-Mate-B (SMB) and gonadotropin releasing-hormone (GnRH) on inducing a fertile estrus and/or ovulation in peripuberal beef heifers. Two hundred and twenty-three, 13 to 15 month peripuberal beef heifers, primarily of Angus or Simmental breeding, were alternately allotted by weight and age within breed to a non-treated control group (C) and three groups which received the SMB treatment regime. Treated groups differed in that one group was inseminated approximately 12 hr after detected in estrus (T) while two other groups were inseminated at a fixed time after implant removal (T-G-I42, T-I48). Heifers in group T-G-I42 received 125 mug GnRH at 30 hr, and were inseminated 42 hr after implant removal. The remaining group of SMB-treated heifers received no additional hormone therapy but were inseminated 48 hr after implant removal (T-I48). Age had no significant effect on estrous response or pregnancy rate nor were there significant age by weight interactions on these parameters. Weight was a significant source of variation on interval from start of breeding to pregnancy (P<.01) and the effect on interval to estrus approached statistical significance (P<.0.9). In control heifers, increased weight had a positive effect on estrous response during the first 21 days of breeding (P<.05). Conversely, weight had no effect on estrous response during the 5-day synchronized period in heifers treated with SMB and observed for estrus (group T). Cumulative estrous response in control heifers was 10, 47, 48 and 55% in 5, 21, 27 and 45 days of breeding, respectively. Cumulative estrous response in SMB-treated heifers obsrved for estrus (group T) was 88, 91, 91 and 91% in 5, 21, 27 and 45 days of breeding, respectively. Pregnancy rate after 5 days of breeding was 9, 27, 18 and 30% for heifers in groups C, T, T-G-I42 and T-I48, respectively. Pregnancy rate after 21 days of breeding for heirfers in groups C, T, T-G-I42 and T-I48, respectively, was 33, 38, 21 and 41%; after 27 days of breeding was 36, 43, 40 and 48%; after 45 days of breeding was 48, 61, 51 and 69% and after the total 88-day breeding season was 59, 68, 71 and 72%. While a large percentage of peripuberal beef heifers with adequate age but insufficient weight were induced into estrus with the SMB treatment, pregnancy rates were low. Timed insemination programs with or without GnRH do not appear to be effective in improving pregnancy response in non-cyclic beef heifers.     

The use of progestins in regimens for fixed-time artificial insemination in beef cattle

Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time Al protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows (n = 111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 microg cloprostenol (PGF) on Day 6 with Al and 100 microg GnRH 60 h later, or PGF on Day 7 with Al and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively (P = 0.96). In Experiment 2. cattle (n = 196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0-7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows (P < 0.8), and 9/23 (39.1 %) versus 17/25 (68.0%) in heifers (P < 0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with Al 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch + CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/ P4 + CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4 + CIDR-B group (75.0%) was higher (P < 0.04) than in the pLH Ovsynch group (37.5%): the pLH Ovsynch + CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch + MGA) or MGA (Days 0-6) plus 2 mg EB and 50 mg progesterone on Day 0. 500 microg PGF on Day 7, 1 mg EB on Day 8 and fixed-time Al 28 h later (EB/ P4 + MGA). Pregnancy rates (P < 0.25) were 44.8% (39/87: Co-Synch), 47.8% (43/90; Co-Synch + MGA), and 60.7% (54/89: EB/P4 + MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time Al.     

The use of GnRH or estradiol to facilitate fixed-time insemination in an MGA-based synchronization regimen in beef cattle

Two experiments were conducted to compare pregnancy rates when GnRH or estradiol were given to synchronize ovarian follicular wave emergence and ovulation in an MGA-based estrus synchronization program. Crossbred beef cattle were fed melengestrol acetate (MGA, 0.5 mg per day) for 7 days (designated days 0-6, without regard to stage of the estrous cycle) and given cloprostenol (PGF; 500 microg intramuscular (im)) on day 7. In Experiment 1, lactating beef cows (n=140) and pubertal heifers (n=40) were randomly allocated to three groups to receive 100 microg gonadorelin (GnRH), 5 mg estradiol-17beta and 100 mg progesterone (E+P) in canola oil or no treatment (control) on day 0. All cattle were observed for estrus every 12 h from 36 to 96 h after PGF. Cattle in the GnRH group that were detected in estrus 36 or 48 h after PGF were inseminated 12 h later; the remainder were given 100 microg GnRH im 72 h after PGF and concurrently inseminated. Cattle in the E+P group were randomly assigned to receive either 0.5 or 1.0 mg estradiol benzoate (EB) in 2 ml canola oil im 24 h after PGF and were inseminated 30 h later. Cattle in the control group were inseminated 12 h after the first detection of estrus; if not in estrus by 72 h after PGF, they were given 100 microg GnRH im and concurrently inseminated. In the absence of significant differences, all data for heifers and for cows were combined and the 0.5 and 1.0 mg EB groups were combined into a single estradiol group. Estrus rates were 57.6, 57.4 and 60.0% for the GnRH, E+P and control groups, respectively (P=0.95). The mean (+/-S.D.) interval from PGF treatment to estrus was shorter (P<0.001) and less variable (P<0.001) in the E+P group (49.0+/-6.1 h) than in either the GnRH (64.2+/-15.9 h) or control (66.3+/-13.3 h) groups. Overall pregnancy rates were higher (P<0.005) in the GnRH (57.6%) and E+P (55.7%) groups than in the control group (30.0%) as were pregnancy rates to fixed-time AI (47.5, 55.7 and 28.3%, respectively). In Experiment 2, 122 crossbred beef heifers were given either 100 microg GnRH or 2 mg EB and 50 mg progesterone in oil on day 0 and subsequently received either 100 microg GnRH 36 h after PGF and inseminated 14 h later or 1 mg EB im 24 h after PGF and inseminated 28 h later in a 2 x 2 factorial design. Pregnancy rates were not significantly different among groups (41.9, 32.2, 33.3 and 36.7% in GnRH/GnRH, GnRH/EB, EB/GnRH and EB/EB groups, respectively). In conclusion, GnRH or estradiol given to synchronize ovarian follicular wave emergence and ovulation in an MGA-based synchronization regimen resulted in acceptable pregnancy rates to fixed-time insemination.     

Pregnancy rate of Nelore females inseminated with male-sexed semen

Pregnancy rates of Nelore females inseminated with male-sexed semen and conventional semen from the same bulls were evaluated. The females included 433 heifers (2 years old) and 230 non-suckling cows, totaling 663 animals. Average body condition score was 3.5 (1-5 scale). Estrus was induced with prostaglandin F2α. The total pregnancy rate of females inseminated with male-sexed semen of bulls A, B and C was 38.8% (131/338) less (P<0.0001) than the total pregnancy rate observed for females inseminated with conventional semen from the same bulls (57.9% [188/325]). Pregnancy rates of non-suckling cows inseminated with male-sexed semen was 43.3% (49/113), which was similar (P≥0.05) to the values found for heifers inseminated with male-sexed semen from the same bulls (36.4% [82/225]). The pregnancy rate of females inseminated with male-sexed semen was less compared with females inseminated with conventional semen. In addition, there was no significant difference in the pregnancy rate of heifers versus non-suckling cows.     

Influence of summer heat stress on pregnancy rates of lactating dairy cattle following embryo transfer or artificial insemination

Lactating Holstein cows were used to determine if pregnancy rate from embryo transfer (n = 113) differed from contemporary control cows (n = 524) that were artificially inseminated (AI). Holstein heifers (n = 55) were superovulated with FSH-P (32 mg total) and inseminated artificially during estrus and subsequently managed under shade structures. On Day 7 post estrus, embryos were recovered, and primarily excellent to good quality embryos (90.3%) were transferred to estrus-synchronized lactating cows. Cows were managed under conditions of exposure to summer heat stress. Pregnancy status was determined by milk progesterone concentrations at Day 21 and palpation per rectum at 45 to 60 d post estrus. Pregnancy rates of cows presented for AI (Day 21, 18.0%; Days 45 to 60, 13.5%) were typical for lactating cows inseminated during periods of summer heat stress in Florida. Pregnancy rates of embryo recipient cows were higher (P<0.001) than those of control cows (Day 21, 47.6%; Days 45 to 60, 29.2%). Summer heat stress had no adverse effect on heifer superovulatory response, but it increased (P<0.05) the incidence of retarded embryos (相似文献   

Luteal function,largest follicle,and fertility in postpartum dairy cows treated with 14dCIDR-PGF2α versus 2xPGF2α-Ovsynch for timed AI

A method for timed artificial insemination (AI) that is used for beef cows, beef heifers, and dairy heifers employs progesterone-releasing inserts, such as the controlled internal drug release (CIDR; Zoetis, New York, NY, USA) that are left in place for 14 days. The 14-day CIDR treatment is a method of presynchronization that ensures that cattle are in the late luteal phase of the estrous cycle when PGF_2α is administered before timed AI. The objective of this study was to test the effectiveness of the 14dCIDR-PGF_2α program in postpartum dairy cows by comparing it with the traditional “Presynch-Ovsynch” (2xPGF_2α-Ovsynch) program. The 14dCIDR-PGF_2α cows (n = 132) were treated with a CIDR insert on Day 0 for 14 days. At 19 days after CIDR removal (Day 33), the cows were treated with a luteolytic dose of PGF_2α, 56 hours later were treated with an ovulatory dose of GnRH (Day 35), and 16 hours later were inseminated. The 2xPGF_2α-Ovsynch cows were treated with a luteolytic dose of PGF_2α on Day 0 and again on Day 14. At 12 days after the second PGF_2α treatment (Day 26), the cows were treated with GnRH. At 7 days after GnRH, the cows were treated with PGF_2α (Day 33), then 56 hours later treated with GnRH (Day 35), and then 16 hours later were inseminated. There was no effect of treatment or treatment by parity interaction on pregnancies per AI (P/AI) when pregnancy diagnosis was performed on Day 32 (115/263; 43.7%) or Days 60 to 90 (99/263; 37.6%) after insemination. There was an effect of parity (P < 0.05) on P/AI because primiparous cows had lesser P/AI (35/98; 35.7%) than multiparous cows (80/165; 48.5%) on Day 32. Cows observed in estrus after the presynchronization step (within 5 days after CIDR removal or within 5 days after the second PGF_2α treatment) had greater P/AI than those not observed in estrus (55/103; 53.4% vs. 60/160; 37.5%; observed vs. not observed; P < 0.01; d 32 pregnancy diagnosis). When progesterone data were examined in a subset of cows (n = 208), 55.3% of cows had a “prototypical” response to treatment (i.e., the cow had an estrous cycle that was synchronized by the presynchronization treatment and then the cow responded appropriately to the subsequent PGF_2α and GnRH treatments before timed AI). Collectively, cows with a prototypical response to either treatment had 52.2% P/AI that was greater (P < 0.001) than the P/AI for cows that had a nonprototypical response (19%) (P/AI determined at 60–90 days of pregnancy). In conclusion, we did not detect a difference in P/AI when postpartum dairy cows were treated with 14dCIDR-PGF_2α or 2xPGF2α-Ovsynch before timed AI. The primary limitation to the success of either program was the failure of the cow to respond appropriately to the sequence of treatments.     

Comparison of pregnancy rates of repeat-breeder dairy cows given gonadotropin releasing hormone at or prior to the time of insemination

A total of 585 repeat-breeder dairy cows was used to study the effect of GnRH treatment, either at or prior to insemination, on the pregnancy rate. The cows were divided into 6 treatment groups. Cows in Group 1 (n = 142) were observed in estrus, and 11 +/- 0.42 hours (mean +/- SEM) later they were given 100 ug, i.m. gonadotropin releasing hormone (GnRH) and were inseminated. Cows in Group 2 (n = 139) were observed in estrus and were inseminated 11.4 +/- 0.43 hours later. Cows in Group 3 (n = 33) were monitored for estrus with an activated heatmount detector but were not observed in estrus; they were inseminated 1.5 +/- 0.87 hours later and were given 100 ug, i.m. GnRH. Cows in Group 4 (n = 35) were not observed in estrus, but they did activate the heatmount detector and were inseminated 2.2 +/- 0.87 hours later. Cows in Group 5 (n = 107) were observed in estrus, given 100 ug, i.m. GnRH 2.0 +/- 0.40 hours later, and were inseminated 9 +/- 0.60 hours after GnRH treatment. Cows in Group 6 (n = 129) were observed in estrus and were inseminated 10 +/- 0.50 hours later. Pregnancy rates were analyzed by Chi-square. Interactions between pregnancy rate, treatment and time of insemination were evaluated using ANOVA and LSM (P < 0.05). There was no effect on pregnancy rate when GnRH was given at or prior to insemination. Cows inseminated on the basis of observed estrus had a higher pregnancy rate (P < 0.05) than cows inseminated on the observation of an activated heatmount detector. From the results of this study, it is concluded that treatment with GnRH at or prior to insemination did not improve the pregnancy rate of repeat-breeder dairy cows.     

Conception, embryonic development and corpus luteum function in beef cattle open for two consecutive breeding seasons

High-fertility (control cows) and low-fertility (cows and heifers not pregnant after two consecutive breeding seasons — twice-open) cyclic bovine females were treated with a single injection of 1000 IU of human chrionic gonadotropin (HCG) or 100 μg of gonadotropin releasing hormone (GnRH) to enhance and/or hasten corpus luteum formation and progesterone secretion, and improve conception rate in the low-fertility females. Hormone treatments were administered to 38 parous control cows, 34 twice-open parous cows, and 27 twice-open nonparous heifers immediately after natural mating by a fertile bull. Blood samples were collected on Days 3, 6, 9, 12, and 18 after mating for determination of systemic progesterone concentrations. Pregnancy rate at necrospy approximately 33 days after mating (range 31–37) was higher in control cows (73.0%) than in twice-open cows (48.4%; P<0.05) or twice-open heifers (34.6%; P<0.01). Pregnancy rate was not affected by the HCG or GnRH treatment. The HCG treatment increased plasma progesterone concentrations in twice-open heifers but not in control or twice-open cows. Progesterone was unaffected by the GnRH treatment. Systemic progesterone concentrations were higher in control than in twice-open females but did not differ between pregnant and nonpregnant females of Days 3, 6, 9 and 12 after mating. Enhanced gonadotropin stimulation at estrus by injection of either HCG or GnRH did not increase pregnancy rate or systemic progesterone concentrations (except in HCG-treated twice-open heifers) in low- or high-fertility females. Lower pregnancy rates in twice-open females were not associated directly with the lower systemic progesterone concentrations.     

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 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, 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% ).     

Selected times of insemination with microencapsulated bovine spermatozoa affect pregnancy rates of synchronized heifers

This experiment was designed to test whether spermatozoa encapsulated in an alginate poly-L-lysine matrix had an extended fertile life in vivo after insemination. Estrus was synchronized in 417 primiparous Friesian and Jersey heifers with a system based on a CIDR-B intravaginal device before the heifers were inseminated either during proestrus (24 h after device removal) or at estrus (48 h after device removal). Pregnancy rates to first inseminations did not differ between the 24 and 48 h inseminations (61 vs 60.6%) with liquid semen diluted in Caprogen (control) but differed with encapsulated semen (45.1 vs 68.6%). The difference in pregnancy rates between the 2 types of semen was more pronounced (P < 0.08) in the animals that were visually detected in estrus. The mean survival time of spermatozoa in the female reproductive tract following insemination at the 24-h insemination time was estimated to be 50 +/- 7.5 h. The increased pregnancy rate with insemination of encapsulated spermatozoa at 48 h could have been due to this process predisposing spermatozoa to capacitate soon after insemination.     

Induction of ovulatory estrus and fertility in non-cycling buffaloes with norgestomet during low breeding season

Field trials were designed to evaluate use of norgestomet treatment to induce ovulatory estrus in non-cycling buffalo cows and heifers during low breeding season. Twenty-five buffalo cows and 50 heifers under village management were given a 9-day treatment with a polymer implant containing 6 mg norgestomet with IM injections of 5 mg estradiol valerate + 3 mg norgestomet at the time of implantation and 600 IU PMSG when the implant was removed. Fifty animals served as controls without any treatment. Seventy-four treated animals showed estrus during the period between 36 to 80 hours after removal of the implant. Twenty-five buffalo cows and 40 heifers that could be further followed up were inseminated twice at 8-hour intervals, 12 hrs after induction of estrus with chilled semen by recto-vaginal method. Of these, 15 (23.1%) conceived, 9 (36%) among buffalo cows and 6 (15%) among heifers. Fourteen buffalo cows and 30 heifers that did not conceive manifested cyclic estrus at an interval of 22.4 and 20.6 days. The conception rate in the cyclic estrus was 57% and 23.3%, respectively, for buffalo cows and heifers. The overall conception rate over two inseminations was 46.2%, 68% in buffalo cows and 32.5% in heifers. In the control group, five (10%) showed spontaneous estrus and two (40%) conceived during the period of the experiment.     

Fertility of swamp buffalo following the synchronization of ovulation by the sequential administration of GnRH and PGF2alpha combined with fixed-timed artificial insemination

This study evaluated fertility in swamp buffalo after synchronization of ovulation combined with fixed time artificial insemination. At the start of the study, designated day 0, from a group of 98 female Thai swamp buffalo, 55 buffalo (heifers n° = 20 and cows n° = 35) were selected to be synchronized with GnRH (Day 0) followed by PGF₂alpha (Day 7) and a second treatment with GnRH (Day 9). All buffalo were inseminated at two fixed times 12 h and 24 h after the second injection of GnRH (Ovsynch+TAI group); a second group of 43 buffalo (heifers n° = 19 and cows n° = 24) were not treated and were artificially inseminated (AI) at natural estrus (AI group). Blood samples were taken 22 days after insemination to evaluate progesterone plasma levels. In the Ovsynch+TAI group, overall conception rate (CR; i.e. the number of cows with progesterone >4.0 ng/ml on day 22 after AI divided by the number of animals inseminated), was 38.1% and overall pregnancy rate (PR; i.e. the number of cows that were pregnant at day 50-60 after insemination divided by the number of animals inseminated), was 32.7%. In the AI group overall CR and PR was 34.9%.Within the Ovsynch+TAI group, CR and PR were reduced (P < 0.05) in heifers compared with cows (CR 15.0% vs. 51.4% for heifers and cows, respectively; PR 15.0% vs. 42.9% for heifers and cows, respectively). Within the AI group the efficacy of treatment was similar between heifers and cows (CR and PR 31.6% for heifers and 37.5% for cows).In conclusion, this study indicates that in swamp buffalo it is possible to synchronize ovulation and use timed artificial insemination with the Ovsynch+TAI protocol.     

Does intrauterine site of insemination in cattle really matter?

Two trials were conducted to determine the influence of semen placement on pregnancy rate in dairy heifers and cows. Seventy-two dairy heifers were artificially inseminated (AI) 10 to 12 h after the first detection of estrus. Control heifers (n = 25) were inseminated at the junction of the uterine body and internal cervical os. The remaining heifers were inseminated deep in one uterine horn, 3 to 5 cm anterior to the external bifurcation. Twenty-three heifers were inseminated in the horn ipsilateral to the ovary bearing the ovulatory follicle, and 24 heifers were inseminated in the contralateral horn. Pregnancy rates did not differ for the three groups of heifers. In a second trial, 64 inseminations were performed in 38 nonlactating, adult dairy cattle. Thirty-one inseminations were made deep in the uterine horn ipsilateral to the ovary bearing the ovulatory follicle and 33 in the contralateral horn. Pregnancy rates were similar for both groups. Combining both trials, pregnancy rates for ipsilateral and contralateral inseminations were equal (32 54 = 59% and 34 57 = 60% , respectively). Therefore, placement of semen in one horn of the uterus does not appear to be a cause of decreased or increased pregnancy rate with AI.     

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.     

The effect of a progesterone releasing intravaginal device (PRID) on pregnancy risk to fixed-time insemination following diagnosis of non-pregnancy in dairy cows

The objective was to compare the probability of pregnancy after fixed-time insemination in cows diagnosed as non-pregnant and re-inseminated following the Ovsynch protocol, with or without exogenous progesterone. Cows (n=415) used in this study originated from 25 farms. Upon diagnosis of non-pregnancy between 30 and 60 days after AI, cows were randomly assigned to receive either a progesterone releasing intravaginal device (PRID; n=208) or a placebo intravaginal device (PID; n=207). All cows received GnRH at enrollment (Day 0), PGF(2alpha) concurrent with intravaginal device removal 7 days later, GnRH on Day 9 and fixed-time insemination 16h later (Day 10). Cows observed in estrus prior to Day 7, had the device removed and were inseminated. Ovaries were examined by transrectal palpation at the time of enrollment and the prominent structures were assessed and recorded. Body condition score, lameness status, interval from previous insemination, and times bred at enrollment were recorded. At intravaginal device removal, the occurrence and intensity of vaginitis was determined according to the amount of debris on the device. Overall, the intravaginal device retention rate was 91%. A total of 5.2% of PID-treated cows and 2.9% of PRID-treated cows were detected in estrus within the 7 days treatment period. Pregnancy status was diagnosed between 30 and 56 days after insemination and all cows were followed for a minimum of 150 days after enrollment. Approximately 28% of cows had evidence of mild vaginitis in response to the intravaginal device, whereas 6% of cows had copious debris associated with the intravaginal device at removal. The probability of pregnancy after fixed-time insemination was 43.8% versus 34.9% in PRID-treated versus PID-treated animals. Exogenous progesterone provided through an intravaginal device to non-pregnant cows that had not displayed estrus improved the probability of pregnancy after fixed-time AI.     

Effect of resynchronization with GnRH on day 21 after artificial insemination on pregnancy rate and pregnancy loss in lactating dairy cows

The objectives of the present study were to determine the effects of resynchronization with GnRH on Day 21 after artificial insemination (AI) on pregnancy rate and losses of pregnancy in lactating dairy cows. Holstein cows (n=585) on two dairy farms were assigned to one of two treatments in a randomized complete block design. On Day 21 after a pre-enrollment AI, animals assigned to the resynchronization (RES) group received 100 microg of GnRH i.m., whereas animals in the control (CON) group received no treatment. All animals were examined ultrasonographically on Days 21 and 28 after AI, and blood samples were taken for progesterone measurement on Day 21. Pregnancy was diagnosed on Day 28 and reconfirmed 14 days later. Nonpregnant cows on Day 28 were inseminated using timed AI after the completion of the Ovsynch protocol 10 and 17 days after enrollment in the study for RES and CON groups, respectively. Progesterone concentration > or =2.35 ng/ml was used as an indicator of pregnancy on Day 21. For RES and CON cows, pregnancy rate at Days 21 (70.9% versus 73.0%, P<0.56), 28 (33.1% versus 33.6%; P<0.80) and 42 (27.0% versus 26.8%; P<0.98) after the pre-enrollment AI did not differ. Administration of GnRH on Day 21 after AI had no effect on pregnancy loss in RES and CON groups from days 21 to 28 (53.2% versus 53.5%; P<0.94) and days 28 to 42 (17.9%; P<0.74) after AI. Pregnancy rate after the resynchronization period was similar for both treatment groups. Resynchronization with GnRH given on Day 21 after AI for initiation of a timed AI protocol prior to pregnancy diagnosis does not affect pregnancy rate and pregnancy loss in lactating dairy cows.     

Evaluation of the 5-day versus a modified 7-day CIDR breeding program in dairy heifers

Dairy heifers were used to compared the effects of two timed AI + controlled internal drug release (CIDR) protocols (5-day vs. a modified 7-day) on: (1) luteal regression to initiate a new ovarian follicular wave; (2) ovarian response to the initial GnRH injection; and (3) pregnancy outcomes. Holstein heifers (N = 543) were assigned randomly to two treatments: (1) 25 mg PGF_2α (im) and a CIDR insert on Day −7 followed by 100 μg of GnRH (GnRH-1) on Day −5 and 25 mg PGF_2α (im) at CIDR insert removal (7-day [7D]) on Day 0; or (2) 100 μg GnRH (GnRH-1) and insertion of a CIDR on Day −5 and 25 mg PGF_2α (im) at CIDR removal (5-day [5D]) on Day 0. Insemination with frozen-thawed conventional or gender-biased semen occurred after detected estrus from Days 0 to 2 or by appointment at 72 h after PGF_2α when a second 100-μg dose of GnRH was given. Blood was collected on Days −7, −5, 0, and 3 to determine concentrations of progesterone and incidence of luteolysis. Ovaries were scanned on Days −5 and 0. Luteolysis in the 7D treatment by 48 h after the initial PGF_2α was greater (P < 0.01) than what occurred spontaneously in the 5D treatment (36.2% vs. 19.7%, respectively). Incidence of ovulation after GnRH-1 on Day −5 was greater (P < 0.05) for 7D than for 5D heifers, but the proportion of heifers with an induced CL on Day 0 did not differ between treatments. Heifers inseminated after detected estrus (166/543, 30.6%) on Days 0, 1, and 2 had greater (P < 0.05) pregnancy per AI (P/AI) at 32 days post AI than after timed AI (38.2% vs. 28.3%) on Day 3. Pregnancy P/AI, however, was greater (P < 0.05) for 7D heifers inseminated at estrus (46.5%) than for 7D heifers receiving the timed AI (26.8%) and differed (P < 0.05) from all 5D heifers regardless of insemination time at estrus (30.5%) or at timed AI at 72 h (29.9%). At the Florida location in which conventional and sexed semen were used during two breeding clusters, P/AI using sexed semen (43.9%, N = 56) did not differ from that of conventional semen (21.2%, N = 50). Remaining replicates of sexed semen produced similar P/AI at the other two locations (sexed = 27.6%, N = 71; and sexed = 31.9%, N = 215). We concluded that the modified 7-day CO-Synch + CIDR program produced more P/AI in heifers inseminated at estrus than a standard 5-day CO-Synch + CIDR program, but when timed AI occurred at 72 h after PGF_2α and CIDR insert removal, P/AI did not differ between programs.     

Endogenous hormone response and fertility in dairy heifers after treatment with Lutalyse and GnRH

Fifty-five dairy heifers were given two injections of Lutalyse 11 days apart. Twenty-one of the heifers were also given an injection of GnRH 48 hr after the second Lutalyse injection (Group G). Of the remaining 34 animals, 19 were randomly allotted to be inseminated 12 hr after observed estrus following Lutalyse (Group E), while 15 were inseminated 80 hr after the second Lutalyse injection (Group P). The intervals from second Lutalyse injection to occurrence of both estrus and peak gonadotropin concentrations were variable among animals receiving only Lutalyse. GnRH injections reduced variation (P<.01) in the interval from second Lutalyse injection to occurrence of peak gonadotropin concentrations, but did not improve fertility. Pregnancy rates did not differ (P>.05) among treatment groups. The failure of GnRH administration following Lutalyse to improve pregnancy rates indicates that GnRH administration followed by insemination 12 hr later is not effective in increasing pregnancy rates above those attained in animals inseminated at either 12 hr post estrus or 80 hr after second Lutalyse injection.