Influence of deslorelin (GnRH-agonist) implant on plasma progesterone, first wave dominant follicle and pregnancy in dairy cattle

The objectives of this study were to investigate the effect of a synthetic GnRH-agonist (Deslorelin) implant on CL function and follicle dynamics when administered 48 h after PGF2 alpha, in a timed-insemination protocol, and to determine if the incorporation of a Deslorelin implant into a timed-insemination protocol to synchronize ovulation would be beneficial to the establishment of pregnancy. In Experiment 1, 15 non lactating cyclic Holstein cows received Buserelin (8 micrograms, i.m.) on Day-9, Lutalyse (25 mg, i.m.) on Day-2, and then on Day 0 received either a Deslorelin implant (700 micrograms, s.c.; n = 5), Buserelin (8 micrograms, i.m.; n = 5), or no treatment (control; n = 5). Blood samples were collected on Days-9, -2, 0 and thereafter daily until the next ovulation. Ovaries were scanned by ultrasound on Days-9, -2, 0, 1 (day of ovulation) and 3 times a week thereafter until a subsequent ovulation. From Days 0 to 15, the rate of increase of plasma progesterone (P4) was greater (P < 0.01) for Deslorelin than for control and Buserelin. Establishment of the first-wave dominant follicle (FWDF) as a Class 3 (> 9 mm) follicle was delayed (P < 0.01) with Deslorelin (14.2 +/- 1.3 d) compared with the control (4.6 +/- 1.3 d) and Buserelin (5.0 +/- 1.5 d) treatments. The FWDF resumed growth after Day 13 in all 5 Deslorelin-treated cows, and 2 cows ovulated spontaneously. In 1 Deslorelin-treated cow, the FWDF regressed, and a second-wave dominant follicle ovulated, while 2 other Deslorelin cows failed to ovulate until after Day 36. The cumulative numbers of Class 2 and 3 follicles was lowest in the Deslorelin group (P < 0.01), while the cumulative number of Class 1 follicles was highest (Deslorelin > Buserelin > Control; P < 0.01). The number of days to CL-regression and days to subsequent estrus did not differ (P > 0.05) among treatments. In Experiment II, 16 lactating potentially subfertile (body condition score 2.25) cows received Cystorelin (100 micrograms, i.m.; Day-9), Lutalyse (25 mg, i.m.; Day-2), and either a Cystorelin injection (100 micrograms, i.m.; n = 8) or Deslorelin implant (700 micrograms, s.c.; n = 8) on Day 0 and inseminated 16 h later. Deslorelin-treated cows had a higher plasma P4 concentration between Days 0 and 16 (P < 0.05) than the 2 other groups, and 5 of the 8 cows in this group were pregnant (Day 45, palpation) compared with 1 of 8 cows in the Cystorelin group (P < 0.05). Incorporation of a Deslorelin implant into a timed-insemination protocol enhanced the pregnancy rate in cows of poor body condition. The results support the hypothesis that enhanced CL function and delayed establishment of the first-wave dominant follicle may enhance embryo survival.     

Effect of hCG administration on day 7 of the estrous cycle on follicular dynamics and cycle length in cows

The use of hCG in cattle at breeding or at different times after breeding has been associated with extension in estrous cycle length among cows that do not become pregnant. The objective of this study was to determine whether the increase in estrous cycle length observed in hCG-treated cows that fail to become pregnant is due to changes in ovarian follicular dynamics. Twelve nonbred lactating cows were randomly assigned either to receive hCG on Day 7 of the cycle (Day 0 = day of estrus, n = 6) or to serve as controls (n = 6). Ultrasound scanning was conducted daily from Day 0 until the onset of the next ovulation to monitor follicular and corpus luteum (CL) dynamics. Blood samples were collected for progesterone analysis at each ultrasound session. Ovulation of the Day 7 follicle occurred in all 6 hCG-treated cows. The time of emergence of the second-wave of follicular growth was advanced in hCG-treated cows but was not statistically different (P > 0.05) from that of the control cows (10.8 +/- 0.3 vs 12.7 +/- 1.4 d). The mean diameter of the second-wave dominant follicle from Days 15 to 18 was not different (P > 0.05) between the treatment groups. However, the second-wave dominant follicle had a slower growth rate (0.8 vs 1.3 mm/d) among cows treated with hCG compared with that of the controls. The second-wave dominant follicle was the ovulatory follicle in 5 control cows, but only in 3 hCG-treated cows. The dominant follicle from the third wave ovulated in 1 control and in 3 hCG-treated cows. The lifespan of the spontaneous CL and the time to low progesterone levels (< 1 ng/ml) were not different between the control and hCG-treated cows. These results suggest an altered follicular dynamic but no extension in estrous cycle length when hCG is administered on Day 7 of the cycle in postpartum cows.     

Embryo recovery and pregnancy rates after the delay of ovulation and fixed time insemination in superstimulated beef cows

The aim of this study was to evaluate the effect of delaying ovulation subsequent to superstimulation of follicular growth in beef cows (Bos indicus) on embryo recovery rates and the capacity of embryos to establish pregnancies. Ovulation was delayed by three treatments using either progesterone (CIDR-B) or a GnRH agonist (deslorelin). Multiparous Nelore cows (n = 24) received three of four superstimulation treatments in an incomplete block design (n = 18 per group). Cows in Groups CTRL, P48 and P60 were treated with a CIDR-B device plus estradiol benzoate (EB, 4 mg, i.m.) on Day-5, while cows in Group D60 were implanted with deslorelin on Day-7. Cows were superstimulated with FSH (Folltropin-V, 200 mg), from Day 0 to 3, using twice daily injections in decreasing amounts. All cows were treated with a luteolytic dose of prostaglandin on Day 2 (08:00 h). CIDR-B devices were removed as follows: Group CTRL, Day 2 (20:00 h); Group P48, Day 4 (08:00 h); Group P60, Day 4 (20:00 h). Cows in Group CTRL were inseminated at 10, 20 and 30 h after first detected estrus. Ovulation was induced for cows in Group P48 (Day 4, 08:00 h) and Groups P60 and D60 (Day 4, 20:00 h) by injection of LH (Lutropin, 25 mg, i.m.), and these cows were inseminated 10 and 20 h after treatment with LH. Embryos were recovered on Days 11 or 12, graded and transferred to synchronized recipients. Pregnancies were determined by ultrasonography around Day 100. Data were analyzed by mixed procedure, Kruskal-Wallis and Chi-square tests. The number of ova/embryos, transferable embryos (mean +/- SEM) and pregnancy rates (%) were as follows, respectively: Group CTRL (10.8+/-1.8, 6.1+/-1.3, 51.5), P48 (12.6+/-1.9, 7.1+/-1.0, 52.3), P60 (10.5+/-1.6, 5.7+/-1.3, 40.0) and D60 (10.3+/-1.7, 5.0+/-1.2, 50.0). There were no significant differences among the groups (P > 0.05). It was concluded that fixed time AI in association with induced ovulation did not influence embryo recovery. Furthermore, pregnancy rates in embryos recovered from cows with delayed ovulation were similar to those in embryos obtained from cows treated with a conventional superstimulation protocol.     

Studies of FSH-P induced follicular growth in cows

Because cow ovaries do not contain a dominant follicle before Day 3 of the estrous cycle, we hypothesized that gonadotropin treatment early in the estrous cycle would induce growth of multiple follicles and could be used to induce superovulation. In Experiment 1, when 16 cows were treated with FSH-P beginning on Day 2 of the estrous cycle and were slaughtered on Day 5, all cows responded to gonadotropin treatment by exhibiting a large number ( approximately 19) of estrogenactive follicles >/= 6 mm. In Experiment 2, in response to FSH-P treatment from Day 2 to Day 7, and fenprostalene treatment on Day 6, 11 of 15 cows exhibited estrus and had a mean ovulation rate of 23.7 +/- 1.5. In Experiment 3, an FSH-P treatment regimen identical to that used in Experiment 2 was administered to cows beginning either on Day 2 (Day-2 cows; n=14) or Day 10 (Day-10 cows; n=11) of the estrous cycle. Twelve of 14 Day-2 cows and all Day-10 cows exhibited estrus after fenprostalene treatment. Day-2 cows exhibited 34.3 +/- 7.0 ovulations, which was less (P < 0.05) than that exhibited by Day-10 cows (48.3 +/- 4.4). However, the proportion of embryos recovered per corpus luteum was about 2-fold greater (P < 0.05) for Day-2 cows than for Day-10 cows (0.49 +/- 0.08 vs 0.27 +/- 0.06). These data indicate that beginning gonadotropin treatment early in the estrous cycle, when a dominant follicle is not present, provides an efficacious means to induce growth of multiple follicles and superovulation in cows. However, when FSH was administered for 6 d, beginning the treatment on Day 10 also resulted in a consistent and efficacious response.     

Fertility in postpartum dairy cows in winter or summer following estrus synchronization and fixed time AI after the induction of an LH surge with GnRH or hCG

In this study, the fertility of postpartum dairy cows after a sequence of treatments with GnRH (Day 0), PGF2alpha (Day 7) and GnRH (Day 9) (GnRH group; n = 164) or hCG (Day 0), PGF2alpha (Day 7) and hCG (Day 9) (group hCG; n = 166) was investigated in summer and winter seasons. All cows were artificially inseminated without estrus detection, 16-18 h after the end of treatment. Control cows (CONT; n = 226) were not treated and were inseminated at natural estrus. The pregnancy rates at Day 90 (46% versus 33%; P < 0.05) and at Day 135 (76% versus 62%; P < 0.05) postpartum were significantly lower in CONT cows in summer compared to winter months but this effect was not observed in the two treated groups. The number of days from calving to conception was significantly lower in GnRH and hCG treatment groups compared to CONT cows in cold months (102 +/- 3.2, 106 +/- 4.2, 126 +/- 3.1, respectively; P < 0.001) and in hot months (112 +/- 3.2, 114 +/- 4.2, 139 +/- 3.1, respectively; P < 0.001). The concentration of insulin was significantly higher in winter (P < 0.001). There were no differences in average plasma concentration of glucose (P = 0.474), GH (P = 0.441) or IGF-I (P = 0.190). In conclusion, we have shown that veterinary supervision combined with a program of estrous synchronization and fixed time insemination can improve fertility of cows suffering heat stress.     

Humoral immune response in lactating dairy cows after repeated exposure to human chorionic gonadotropin

Our objective was to determine if repeated exposure of lactating dairy cows to human chorionic gonadotropin (hCG) would induce an antibody (Ab) response against hCG. Cows either received an hCG injection (hCG; n = 24, each given 2000 IU im) or no treatment (CON; n = 22) 18 days after a timed AI (TAI) and 7 days before initiation of Ovsynch for resynchronization of ovulation and TAI. A subgroup of cows continued in the experiment to receive a second hCG injection (n = 17) 35 days after the first exposure to hCG, whereas another subgroup served as controls (n = 9). Another subgroup of cows continued in the experiment to receive a third hCG injection (n = 11) 35 days after the second exposure to hCG, whereas cows not receiving hCG served as controls (n = 8). A binding radioimmunoassay was used to detect hCG antibodies in serum samples collected 0, 7, 14, 21, and 28 days after treatment. A positive Ab response (>6.2% bound) was defined as three standard deviations above CON binding. No cows had hCG antibodies at Day 0 before the first exposure to hCG. After the first hCG treatment, there was no difference (P = 0.52) between Ab positive cows in CON (0%) and hCG (4%) treatments. At the second hCG treatment, on Day 0 there was no difference (P = 0.65) between CON (0%) and hCG (6%) cows, whereas, more (P = 0.02) hCG cows (47%) were positive than CON cows (0%) within 28 days of the hCG injection. At the third hCG injection, hCG cows tended (P = 0.09) to have a greater percentage of Ab positive (36%) than CON cows (0%), whereas after the injection, a greater (P < 0.01) percentage of hCG cows were positive (hCG = 73% vs. CON = 0%). After the second and third exposure to hCG, 8 of 17 and 8 of 11 cows within the hCG group had greater percent Ab bound at 7, 14, 21, and 28 days after hCG than cows in CON and those with no Ab response. The greatest percent Ab binding occurred at 14 days after the second and third hCG exposure. We concluded that some but not all lactating dairy cows developed an Ab response after repeated exposure to hCG and that maximum response occurred within 14 days after hCG exposure.     

The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG

The induction of optimal synchrony of estrus in cows requires synchronization of luteolysis and of the waves of follicular growth (follicular waves). The aim of this study was to determine whether hormonal treatments aimed at synchronizing follicular waves improved the synchrony of prostaglandin (PG)-induced estrus. In Experiment 1, cows were treated on Day 5 of the estrous cycle with saline in Group 1 (n = 25; 16 ml, i.v., 12 h apart), with hCG in Group 2 (n = 27; 3000 IU, i.v.), or with hCG and bovine follicular fluid (bFF) in Group 3 (n = 21; 16 ml, i.v., 12 h apart). On Day 12, all cows were treated with prostaglandin (PG; 500 micrograms cloprostenol, i.m.). In Experiment 2, cows were treated on Day 5 of the estrous cycle with saline (3 ml, i.m.) in Group 1 (n = 22) or with hCG (3000 IU, i.v.) in Group 2 (n = 20) and Group 3 (n = 22). On Day 12, the cows were treated with PG (500 micrograms in Groups 1 and 2; 1000 micrograms in Group 3). Blood samples for progesterone (P4) determination were collected on Day 12 (Experiment 1) or on Days 12 and 14 (Experiment 2). Cows were fitted with heat mount detectors and observed twice a day for signs of estrus. Four cows in Experiment 1 (1 cow each from Groups 1 and 2; 2 cows from Group 3) had plasma P4 concentrations below 1 ng/ml on Day 12 and were excluded from the analyses. In Experiment 1, cows treated with hCG or hCG + bFF had a more variable (P = 0.0007, P = 0.0005) day of occurrence of and a longer interval to estrus (5.9 +/- 0.7 d, P = 0.003 and 6.2 +/- 0.8 d, P = 0.005) than saline-treated cows (3.4 +/- 0.4 d). The plasma P4 concentrations on Day 12 were higher (P < 0.0001) in hCG- and in hCG + bFF-treated cows than in saline-treated cows (9.4 +/- 0.75 and 8.5 +/- 0.75 vs 4.1 +/- 0.27 ng/ml), but there was no correlation (P > 0.05) between plasma P4 concentrations and the interval to estrus. In Experiment 2, cows treated with hCG/500PG and hCG/1000PG had a more variable (P = 0.0007, P = 0.002) day of occurrence of and a longer interval to estrus (4.2 +/- 0.4 d, P = 0.04; 4.1 +/- 0.4 d, P = 0.03) than saline/500PG-treated cows (3.2 +/- 0.1 d). The concentrations of plasma P4 on Days 12 and 14 of both hCG/500PG- and hCG/1000PG-treated cows were higher (P < 0.05) than in saline/500PG-treated cows (7.3 +/- 0.64, 0.7 +/- 0.08 and 7.7 +/- 0.49, 0.7 +/- 0.06 vs 5.3 +/- 0.37, 0.5 +/- 0.03 ng/ml). The concentrations of plasma P4 on Days 12 or 14 and the interval to estrus were not correlated (P > 0.05) in any treatment group. The concentrations of plasma P4 on Days 12 and 14 of hCG/500PG- or hCG/1000PG-treated cows were correlated (r = 0.65, P < 0.05; r = 0.50, P < 0.05). This study indicated that treatment of cows with hCG on Day 5 of the estrous cycle reduced the synchrony of PG-induced estrus and that this reduction was not due to the failure of luteal regression.     

The effect of administering equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) post artificial insemination on fertility of lactating dairy cows

The objective was to evaluate the effect of equine chorionic gonadotropin (eCG) and hCG post artificial insemination (AI) on fertility of lactating dairy cows. In Experiment 1, cows were either treated with eCG on Day 22 post AI (400 IU; n = 80) or left untreated (n = 84). On Day 29, pregnant cows were either treated with hCG (2500 IU; n = 32) or left untreated (n = 36). Pregnancy and progesterone were evaluated on Days 29 and 45. In Experiment 2, cows (n = 28) were either treated with eCG on Day 22 (n = 13) or left untreated (n = 15) and either treated with hCG on Day 29 (n = 14) or left untreated (n = 14). Blood sampling and ultrasonography were conducted between Days 22 and 45. In Experiment 3, cows were either treated with eCG on Day 22 post AI (n = 229) or left untreated (n = 241). Pregnancy was evaluated on Days 36 and 85. In Experiment 1, eCG on Day 22 increased (P < 0.02) the number of pregnant cows on Day 29 (50.0 vs. 33.3%) and on Day 45, the increase was higher (P < 0.01) in cows with timed AI (41.2 vs. 6.5%) than in cows AI at detected estrus (50.0 vs. 37.8%). Pregnancy losses were reduced by eCG and hCG, but increased in cows that did not receive eCG but were given hCG (P < 0.01). Treatment with hCG tended (P < 0.06) to increase progesterone in control cows, but not in cows treated with eCG. In Experiment 2, hCG increased (P < 0.01) the number of accessory CLs on Day 35 (28.5 vs. 0.0%) and tended (P < 0.07) to increase progesterone. In Experiment 3, eCG increased the number of pregnant cows (P < 0.05) on Days 36 and 85, but only in cows with low body condition (eCG = 45.6 and 43.5%; Control = 22.9 and 22.9%). In conclusion, eCG at 22 days post insemination increased fertility, primarily in cows with low body condition and reduced pregnancy losses when given 7 days before hCG; hCG induced accessory CLs and slightly increased progesterone, but hCG given in the absence of a prior eCG treatment reduced fertility.     

The effect of hCG administration five days after insemination on the first service conception rate of anestrous dairy cows

The aim of this study was to investigate the effect of treating anovulatory anestrous (AA) dairy cows with 1500 IU of hCG IM, 5 d after insemination, on their first service conception rate. A clinical trial was conducted during the 2003/2004 breeding season involving 442 AA dairy cows in six herds. On Day -8, all cows were treated with a progesterone-containing intravaginal device (Cue-Mate). The devices were removed on Day -2, and on Day -1 all cows received an IM injection of 1mg of estradiol benzoate. Cows in the control group (n=220) received no further treatments. Cows in the treatment group (n=222) which had been inseminated on Days 0 or 1 were treated with 1500 IU of hCG IM 5 d after insemination. Blood was collected from 30 cows (15 in each group) on Days 5 and 12 after AI for analysis of plasma P4 concentration. There was no difference in first service conception rates between the control and treatment groups (46.3% versus 43.6%, respectively; P=0.68), despite the fact that plasma P4 concentrations were higher in the treatment group on Day 12 (4.9+/-1.3 ng/mL versus 6.2+/-2.7 ng/mL for control and treatment groups, respectively; P<0.01). In conclusion, 1500 IU of hCG 5 d after insemination did not improve first service conception rate in AA dairy cows.     

Follicular growth, ovulation and embryo recovery in dairy cows given FSH at the beginning or middle of the estrous cycle

Variability in the superovulation response is an important problem for the embryo transfer industry. The objective of this study was to determine whether FSH treatment at the beginning of the cycle would improve the ovulation rate and embryo yield in dairy cows. Twenty-eight postpartum cyclic dairy cows were allocated at random to 4 treatment groups (A, B, C and D). Group A cows (n = 10) received FSH (35 mg) at a decreasing dose, starting on Day 9 (Day 0 = day of estrus) for 5 days followed by PGF(2alpha) (35 mg) on Day 12. Cows assigned to Groups B, C and D (n = 6 cows each, respectively) were given 35 mg FSH at a decreasing dose from Days 2 to 6 followed by PGF(2alpha) on Day 7. Group C and D cows received PRID inserts from Day 3 to Day 7. Cows in Group D additionally received 1000 IU hCG 60 hours after PGF(2alpha) treatment. Ovaries were scanned daily using a real time ultrasound scanner from the beginning of FSH treatment until embryo recovery, to monitor follicular development, ovulation and the number of unovulated follicles. Embryos were recovered from the uterus by a nonsurgical flushing technique 7 days after breeding. There were no differences (P>0.01) in the number of follicles > 10 mm at 48 hours after PGF(2alpha) treatment among the 4 groups. The mean numbers of follicles were 10.6 +/- 1.2, 9.3 +/- 1.3, 12.2 +/- 1.3 and 15.0 +/- 2.9 for Groups A, B, C and D, respectively. A significantly (P<0.001) higher number of ovulations was observed and a larger number of embryos was recovered in Group A than in the other groups. The results of this study indicate that superovulation with FSH at the beginning of the cycle causes sufficient follicular development but results in very low ovulation and embryo recovery rates.     

Estrus synchronization in beef cows: comparison between GnRH+PGF2alpha+GnRH and PRID+PGF2alpha+eCG

The aim of this study was to compare two protocols for estrus synchronization in suckled beef cows over a 2 years period. The population studied consisted of 172 Charolais and 168 Limousin cows from 12 and 14 beef herds, respectively. In each herd, cows were allotted to groups according to parity, body condition score and calving difficulty. Cows in Group 1 (n=174) received PRID on Day-8 with estradiol benzoate (10mg, vaginal capsule), dinoprost on Day-4 (25mg i.m.), eCG on Day 2 (500 IU i.m.). The PRID was removed on Day-2 and cows were inseminated on Day 0, 56 h after PRID was removed. Cows in Group 2 (n=166) received GnRH on Day-10 (100 microg i.m.), dinoprost on Day-3 (25mg i.m.) and GnRH on Day-1 (100 microg i.m.), and were inseminated on Day 0, 16-24h after the last GnRH treatment. Plasma progesterone concentrations were measured to determine cyclicity prior to treatment (Days-20 and -10), to confirm the occurrence of ovulation (Days 0 and 10) and to determine the apparent early pregnancy rate (Days 0, 10 and 24). Pregnancy diagnosis was performed by ultrasonography between Days 35 and 45. The effects of various factors on ovulation, apparent early pregnancy and pregnancy rates were studied using logistic mixed models. There was no significant difference between Groups 1 and 2, respectively, for the cyclicity rate before treatment (80.5% versus 80.1%), for apparent pregnancy rate on Day 24 (62.1% versus 54.8%, P=0.09) and for pregnancy rate on Days 35-45 (53.8% versus 46.3%, P=0.16). Ovulation rate was higher (P<0.01) in Group 1 (90.8%) than in Group 2 (77.1%) and was affected by cyclicity prior to treatment in Group 2 but not in Group 1 (Group 1: 88.2% in anestrous cows versus 91.4% in cyclic cows; Group 2: 45.5% in anestrous cows versus 85.0% in cyclic cows, P interaction=0.05). Apparent pregnancy rates on Day 24 were influenced by the year of study (52.4% versus 68.8%, OR=2.12, P<0.01) and by the cyclicity before treatment (anestrous cows 46.3% versus cyclic cows 61.5%, OR=1.86, P<0.05). Pregnancy rates at 35-45 days were influenced by the year of study (44.2% versus 59.8%, OR=1.92, P<0.01). In conclusion, although pregnancy rates were similar for the two treatments, the combination of GnRH+PGF2alpha+GnRH in suckled beef cows induced a lower rate of ovulation than treatment with PRID+PGF2alpha, particularly in anestrous cows.     

Characteristics of corpus luteum formed from the first wave dominant follicle following hCG in cattle

Two experiments were conducted to characterize the development and function of corpus luteum (CL) induced by hCG. In Experiment 1, cows (n = 18) were randomly assigned either to serve as controls (CONT, n = 6) or to receive hCG on Day 7 with (hCG-LUT, n = 6), or without (hCG-CONT, n = 6) surgical removal of the spontaneous CL on Day 12. The diameters of the hCG-induced and spontaneous CL of similar age did not differ (P > 0.05) between Days 1 and 4. At Day 5, the CONT (spontaneous) CL diameter (29.3 +/- 1.4 mm) was larger (P < 0.05) than that of the hCG-LUT (24.5 +/- 1.5 mm) or the hCG-CONT (24.6 +/- 1.7 mm) induced CL. Similarly, induced CL diameter for hCG-LUT and hCG-CONT groups was smaller (P < 0.01) than the CONT (spontaneous) CL between Days 10 to 14. Plasma progesterone (P(4)) levels were not different (P > 0.05) among treatment groups until Day 12. On Day 14, the P(4) concentration of hCG-LUT cows decreased (P < 0.01) to 1.1 +/- 0.9 ng/ml, then increased to 3.1 +/- 0.9 ng/ml by Day 18. Comparative values for hCG-CONT and CONT cows were 5.8 +/- 0.8 and 4.2 +/- 0.8; 4.5 +/- 0.8 and 5.5 +/- 0.8 ng/ml, respectively. The onset of regression of CL as well as estrous cycle length were similar (P > 0.05) for all treatment groups. In Experiment 2, the effects of intrauterine infusion of indomethacin on the diameter, function and life span of hCG-induced CL were examined. A slight, albeit not significant, suppression of PGFM levels was observed in indomethacin-infused cows (n = 4) compared with the controls (n = 4) in blood samples obtained once a day during the infusion period. However, in 2 cows from which blood samples were collected every 6 h, the control cow showed several pulses of PGFM while the indomethacin-treated cow exhibited none. Induced CL diameter and lifespan were not affected by indomethacin infusion. However, mean P(4) levels were higher (P < 0.05) between Days 16 and 20 in the indomethacin-infused group. In conclusion, the results suggest that 1) hCG-induced CL are functional but appear to be smaller and secrete less P(4) than spontaneous CL of similar age, and 2) the small size and reduced secretary function observed is not necessarily due to PGF(2alpha) secreted by the uterine endometrium but, probably, to inherent characteristics.     

Failure of human chorionic gonadotropin injections to sustain gonadotropin-releasing hormone-induced corpora lutea in postpartum beef cows

Anestrous postpartum (PP) Hereford cows (n =20) were used to determine the effects of repeated injections of human chorionic gonadotropin (hCG) on the progesterone (P4) secretion and functional lifespan of gonadotropin-releasing hormone (GnRH)-induced corpora lutea (CL). Suckling was reduced to once a day from Day 21 to Day 25 PP, and all cows received injections of 200 micrograms GnRH at 1500 h on Day 24 PP to induce ovulation. Treated cows (HCG, n = 10) received 200 IU hCG b.i.d. from 1900 h on Day 27 PP to 1900 h on Day 33 PP; control cows (CTRL, n=10) were not injected. Blood was collected on Days 21, 23, 25, and 27 to 33, 35, 37, and 39 PP. Serum P4 concentration was measured by radioimmunoassay and used to classify luteal lifespan and the associated estrous cycle as short (SHORT) or normal (NORM) in duration. Treatment with hCG resulted in more (p less than 0.01) cows with SHORT cycles (7 of 9 vs. 4 of 9). Serum P4 concentrations were similar (p greater than 0.20) between groups from 4 days before until 6 days after GnRH injection. Cows with NORM cycles (n = 7) had greater serum P4 concentrations (p less than 0.05) on Days 7 to 11 after GnRH than cows with SHORT cycles (n = 11). By Day 39 PP, all cows with SHORT cycles appeared to have undergone a second ovulation. Charcoal-stripped serum pools from before (PRE) and during hCG injection (INJ) were assayed for total luteinizing hormone-like bioactivity (LH-BA) using a dispersed mouse-Leydig cell bioassay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Presynchronization with GnRH 7 days prior to resynchronization with CO-Synch did not improve pregnancy rate in lactating dairy cows

The objective was to determine the effect of presynchronization with GnRH 7 d prior to the initiation of resynchronization with CO-Synch on pregnancy/AI (P/AI) of resynchronization in lactating dairy cows, and the effect of GnRH on P/AI from previous breeding. All parity Holstein cows (n = 3287) from four dairy farms were enrolled. Cows not detected in estrus by 28 ± 3 d (Day -7) after a previous breeding were assigned to receive either GnRH (100 μg, im; n = 1636) or no GnRH (Control; n = 1651). Cows not detected in estrus during the 7 d after GnRH underwent pregnancy diagnosis (35 ± 3 d after previous breeding, Day 0); non-pregnant cows (n = 1232) in the Control (n = 645) and GnRH (n = 587) groups were resynchronized with a CO-Synch protocol. Briefly, cows received 100 μg GnRH on Day 0, 25 mg PGF_2α on Day 7, and 72 h later (Day 10) were given 100 μg GnRH and concurrently inseminated. Serum progesterone concentrations (n = 55 cows) were elevated in 47.3, 70.9, and 74.5% of cows on Days -7, 0, and 7, respectively. The proportion of cows with high progesterone concentrations on Day -7 and Day 0 were 44.1% and 88.2% (P < 0.003), and 55.2% and 33.2% (P > 0.1), for GnRH and Control groups, respectively. Accounting for significant variables such as locations (P < 0.0001) and parity categories (P < 0.05), the P/AI (35 ± 3 d after AI) for resynchronization was not different between GnRH and Control groups [26.7% (95% CI: 23.2, 30.5; (157/587) vs 28.4% (95% CI: 25.0, 31.9; (183/645); P > 0.1]. There were no significant location by treatment or parity by treatment interactions. Accounting for significant variables such as location (P < 0.0001) and parity categories (P < 0.001), the P/AI was not different between GnRH and Control groups for the previous service [60.2%; 95% CI: 57.9, 62.6; (986/1636) vs 59.1%; 95% CI: 56.7, 61.5; (976/1651); P > 0.1)]. There were no significant location by treatment or parity by treatment interactions. In conclusion, more cows presynchronized with GnRH 7 d prior to resynchronization with CO-Synch had elevated progesterone concentrations at initiation of resynchronization than those not presynchronized. The GnRH treatment 7 d prior to resynchronization with CO-Synch, when given 28 ± 3 d after a previous breeding, did not improve P/AI in lactating dairy cows; furthermore, compared to the control, it did not significantly affect pregnancy rate from the previous breeding.     

Development of a persistent ovarian follicle and associated elevated concentrations of 17beta-estradiol preceding ovulation does not alter the pregnancy rate after embryo transfer in cattle

It was hypothesized that prolonged elevation in 17beta-estradiol (E(2)) preceding ovulation as a result of a persistent ovarian follicle would have a detrimental effect on pregnancy rate after Day 7 (behavioral estrus = Day 0) of the estrous cycle. Cows were either treated with exogenous progesterone (P(4)) for 10 d or remained untreated (CON; n = 76). Cows were treated with 1 of 2 doses of P(4) from Day 6 to 16 which was intended to result in either elevated E(2) (EE(2); n = 76) or normal E(2) (NE(2); n = 76) concentration in the circulation. At the initiation of P(4) treatment, cows received prostaglandin F(2alpha) (PGF(2alpha)) to eliminate the endogenous source of P(4). On Day 16, the exogenous source of P(4) was removed from treated cows, while cows in the CON group received PGF(2alpha). A single embryo was transferred into each cow 7 days after observation of behavioral estrus. Blood samples were taken on alternating days during the treatment period to determine concentrations of P(4) and E(2). The pregnancy rate was determined by ultrasonographic examination 25 to 32 d after embryo transfer. There was a treatment-by-day interaction (P < 0.0001) on E(2) concentrations in the plasma during the 10-d treatment period. Cows in the EE(2) group had a higher concentration of E(2) by Day 8 (6.1 +/- 0.5 pg/ml) and this concentration remained elevated until PRID removal compared with that of cows in the NE(2) (2 +/- 0.2 pg/ml) and CON (2.0 +/- 0.3 pg/ml) groups, which had concentrations of E(2) similar to those at the initiation of treatment. Pregnancy rates after embryo transfer did not differ (P = 0.56; X(2) = 1.1) among cows in the EE(2) (30.7%), NE(2) (36.2%) and CON (32.9%) groups. Prolonged elevation of E(2) concentrations associated with the development of a persistent ovarian follicle preceding ovulation did not affect the pregnancy rate to embryo transfer after Day 7 of the estrous cycle in cows.     

Reproductive performance of postpartum dairy cows under a highly intervenient breeding program involving timed insemination and combinations of GnRH, prostaglandin F2alpha and human chorionic gonadotropin

Lactating Holstein cows (n=288) were grouped as pairs at parturition and randomly assigned to two treatments (control, C vs intervenient treatment, T). The reproductive management of the Group C cows (n=130) consisted of the intramuscular administration of 500 microg PGF2alpha analogue (PG) on Days 28 and 63 postpartum and breeding on the basis of estrus signs with the a.m.-p.m. rule after Day 63. Cows that were not bred by 77 d postpartum received another injection of PG and were bred at estrus or 84 h after PG treatment. Pregnancy diagnoses were perfomed by palpation of the uterus per rectum 42 to 48 d after AI. Cows in the T group (n=139) received intramuscular injections of 100 microg GnRH 14 d and PG 28 d after calving. On Day 56 postpartum, cows were given a second dose of GnRH followed by PG on Day 63 postpartum and a third GnRH injection 48 h after PG (OvSynch). Cows were inseminated at a fixed time (22+/-1 h) after GnRH. Five days after the fixed-time insemination cows were given 1500 IU hCG i.m.. Group C and T cows that returned to service or were diagnosed as non-pregnant continued to receive PG at intervals of 14 d with breeding at estrus or 84 h after the second PGF2alpha dose. A sustained increase in milk progesterone concentration was observed in 59.0% of T cows after GnRH administration on Day 14. A similar rise in milk progesterone concentrations was observed in 53.8% of C cows. The PG on Day 28 induced luteolysis more in Group T cows (53.2%) than in Group C cows (36.9%). The PG on Day 63 reduced milk progesterone concentrations to basal levels in 50.7% of T and 49.2% of Group C animals. The first service pregnancy rates (T, 40.3% vs C, 36.2%) and the overall pregnancy rates (all services, T, 83.5% vs C, 86.9%) were not different between the two groups. The two treatments did not differ in the interval from first service to pregnancy, calving to pregnancy or in calving interval, number of services per pregnancy or culling rates.     

Body condition influences maintenance of a persistent first wave dominant follicle in dairy cattle

The objective of this study was to determine whether plasma concentrations of progesterone (P4) from a controlled internal drug releasing (CIDR) device (approximately 2 ng/ml) were adequate to sustain a persistent first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 +/- 0.72, n = 4]) compared with high body condition (HBC, BCS = 4.4 +/- 0.12, n = 4) nonlactating dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows were treated with PGF2 alpha (25 mg i.m. Lutalyse, P.M., and Day 8 A.M.) and a used CIDR device containing P4 (1.2 g) was inserted into the vagina until ovulation or Day 16. Plasma was collected for P4 and estradiol (E2) analyses from Day 5 to Day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Mean concentrations of plasma P4 were greater in HBC than LBC cows between Days 5 and 7 (4.6 > 3.4 +/- 0.37 ng/ml; P < 0.04). All LBC cows maintained the first wave dominant follicle and ovulated after removal of the CIDR device (18.3 +/- 0.3 d, n = 3; Cow 4 lost the CIDR device on Day 11 and ovulated on Day 15), whereas in the HBC cows ovulation occurred during the period of CIDR exposure (11.3 +/- 0.3 d; n = 3; a fourth cow developed a luteinized first wave dominant follicle that did not ovulate during the experimental protocol on Day 19). Mean day of estrus was 17 +/- 0.4 for LBC (n = 3) and 10 +/- 0.4 for HBC (n = 3) cows. Sustained concentrations of plasma E2 (12.9 +/- 2.8 pg/ml; Days 8 to 17) in LBC cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS on concentrations of plasma P4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressions: yLBC = 19.9 - 3.49x + 0.166x2 vs yHBC = 37.3 - 7.04x + 0.340x2 (x = day of cycle, Days 7 to 12). Although P4 concentration was greater for HBC cows prior to Day 8, a greater clearance of plasma P4 released from the CIDR device in the absence of a CL altered follicular dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P4 was sustained in LBC cows that permitted maintenance of a persistent first wave dominant follicle.     

Effects of flunixin meglumine, recombinant bovine somatotropin and/or human chorionic gonadotropin on pregnancy rates in Nelore cows

The objective was to compare pharmacological strategies aiming to inhibit prostaglandin F2 alpha (PGF_2α) synthesis (flunixin meglumine; FM), stimulate growth of the conceptus (recombinant bovine somatotropin; bST) and progesterone (P₄) synthesis (human chorionic gonadotropin; hCG), as well as their combinations, regarding their ability to improve pregnancy rates in beef cattle. Lactating Nelore cows (N = 975), 35 to 70 days postpartum, were synchronized and inseminated by timed artificial insemination (TAI) on Day 0. On Day 7, cattle were allocated into eight groups and received one of the following treatments: saline (S) on Days 7 and 16 (Group Control); S on Day 7 and FM on Day 16 (Group FM); bST on Day 7 and S on Day 16 (Group bST); bST on Day 7 and FM on Day 16 (Group bST + FM); hCG on Day 7 and S on Day 16 (Group hCG); hCG on Day 7 and FM on Day 16 (Group hCG + FM); bST and hCG on Day 7 and S on Day 16 (Group bST + hCG), or bST and hCG on Day 7 and FM on Day 16 (Group bST + hCG + FM). The aforementioned treatments were administered at the following doses: 2.2 mg/kg FM (Banamine^®; Intervet Schering-Plough, Cotia, SP, Brazil), 500 mg bST (Boostin^®; Intervet Schering-Plough), and 2500 IU hCG (Chorulon^®; Intervet Schering-Plough). Pregnancy diagnosis was performed 40 days after TAI by transrectal ultrasonography. Pregnancy rates were not significantly different among treatments. However, there was a main effect of hCG treatment to increase pregnancy rates (63.0 vs. 55.4%; P = 0.001). Concentrations of P₄ did not differ significantly among groups on Day 7 or on Day 16. However, consistent with the higher pregnancy rates, hCG increased P₄ concentrations on Day 16 (10.6 vs. 9.6 ng/mL, respectively; P = 0.05). We concluded that hCG treatment 7 days after TAI improved pregnancy rates of lactating Nelore cows, possibly via a mechanism leading to induction of higher P₄ concentrations, or by reducing the luteolytic stimulus during maternal recognition of pregnancy.     

Induction of estrus in suckled female yaks (Bos grunniens) and synchronization of ovulation in the non-sucklers for timed artificial insemination using progesterone treatments and Co-Synch regimens

The objectives of the present study were to evaluate the induction of estrus and fertility in yak cows treated with Co-Synch regimens or progesterone (P(4)). In Experiment 1, postpartum suckled yaks were assigned to three treatments: (1) A (n=28), insertion of an intravaginal device containing P(4) (CIDR) on Day 0, PGF(2alpha) (i.m.) on Day 6 and PMSG (i.m.) at the time of CIDR removal on Day 7 (P(4)-PGF(2alpha)-PMSG); (2) B (n=21), PGF(2alpha) (i.m.) on Day 6 and PMSG on Day 7; (3) C (n=26), control group. Seven yak bulls were grazed with the cows for natural breeding. Rate of estrus within 96h of the end of treatment was greater (P<0.05) in A (100.0%) than in B (28.6%) or C (0.0%). First service conception rate (CR) determined by serum P(4) on Day 21 after breeding was greater (P<0.05) in A (78.6%) than in B (22.2%). Also, pregnancy rate (PR) during the breeding season was greater (P<0.05) in A (82.1%) than in B (19.0%) and C (7.7%). In Experiment 2, non-suckled yaks that calved in previous years but not in the current year were assigned to three treatments: (1) A (n=31), GnRH (i.m.) on Day 0, followed by PGF(2alpha) on Day 7 and timed artificial insemination (TAI) concurrently with GnRH treatment on Day 9 (Co-Synch regimen); (2) B (n=50), a CIDR device for 7 days plus PGF(2alpha) and PMSG at the time of CIDR withdrawal on Day 7 and TAI on Day 9 (P(4)-PGF(2alpha)-PMSG); (3) C (n=50), yak cows were artificially inseminated at spontaneous estrus. Frozen semen of Holstein and Jersey were used for insemination in Experiment 2. The CR assessed by rectal palpation 35 days after TAI was not different in A (22.6%), B (30.0%) and C (33.3%), but PR was greater in A and B than in C, when based on those cows presented for estrous synchronization programs. It is concluded that P(4)-PGF(2alpha)-PMSG protocol could efficiently induce estrus and result in an acceptable pregnancy rate in postpartum suckled yak cows. This technique and Co-Synch regimen can be applied successfully for TAI of non-suckled yak cows.     

Effect of transfer of one or two in vitro-produced embryos and post-transfer administration of gonadotropin releasing hormone on pregnancy rates of heat-stressed dairy cattle

Pregnancy rates following transfer of an in vitro-produced (IVP) embryo are often lower than those obtained following transfer of an embryo produced by superovulation. The purpose of the current pair of experiments was to examine two strategies for increasing pregnancy rates in heat stressed, dairy recipients receiving an IVP embryo. One method was to transfer two embryos into the uterine horn ipsilateral to the CL, whereas the other method involved injection of GnRH at Day 11 after the anticipated day of ovulation. In Experiment 1, 32 virgin crossbred heifers and 26 lactating crossbred cows were prepared for timed embryo transfer by being subjected to a timed ovulation protocol. Those having a palpable CL were randomly selected to receive one (n = 31 recipients) or two (n = 27 recipients) embryos on Day 7 after anticipated ovulation. At Day 64 of gestation, the pregnancy rate tended to be higher (P = 0.07) for cows than for heifers. Heifers that received one embryo tended to have a higher pregnancy rate than those that received two embryos (41% versus 20%, respectively) while there was no difference in pregnancy rate for cows that received one or two embryos (57% versus 50%, respectively). Pregnancy loss between Day 64 and 127 only occurred for cows that received two embryos (pregnancy rate at Day 127=17%). Between Day 127 and term, one animal (a cow with a single embryo) lost its pregnancy. There was no difference in pregnancy rates at Day 127 or calving rates between cows and heifers, but females that received two embryos had lower Day-127 pregnancy rates and calving rates than females that received one embryo (P < 0.03). Of the females receiving two embryos that calved, 2 of 5 gave birth to twins. For Experiment 2, 87 multiparous, late lactation, nonpregnant Holstein cows were synchronized for timed embryo transfer as in Experiment 1. Cows received a single embryo in the uterine horn ipsilateral to the ovary containing the CL and received either 100 microg GnRH or vehicle at Day 11 after anticipated ovulation (i.e. 4 days after embryo transfer). There was no difference in pregnancy rate for cows that received the GnRH or vehicle treatment (18% versus 17%, respectively). In conclusion, neither unilateral transfer of two embryos nor administration of GnRH at Day 11 after anticipated ovulation improved pregnancy rates of dairy cattle exposed to heat stress.