Resynchronization with unknown pregnancy status using progestin-based timed artificial insemination protocol in beef cattle

Two experiments were designed to evaluate the use of resynchronization (RESYNCH) protocols using a progestin-based timed artificial insemination (TAI) protocol in beef cattle. In experiment 1, 475 cyclic Nelore heifers were resynchronized 22 days after the first TAI using two different inducers of new follicular wave emergence (estradiol benzoate [EB; n = 241] or GnRH [n = 234]) with the insertion of a norgestomet ear implant. At ear implant removal (7 days later), a pregnancy test was performed, and nonpregnant heifers received a dose of prostaglandin plus 0.5 mg of estradiol cypionate, with a timed insemination 48 hours later. The pregnancy rate after the first TAI was similar (P = 0.97) between treatments (EB [41.9%] vs. GnRH [41.5%]). However, EB-treated heifers (49.3%) had a greater (P = 0.04) pregnancy per AI (P/AI) after the resynchronization than the GnRH-treated heifers (37.2%). In experiment 2, the pregnancy loss in 664 zebu females (344 nonlactating cows and 320 cyclic heifers) between 30 and 60 days after resynchronization was evaluated. Females were randomly assigned to one of two groups (RESYNCH 22 days after the first TAI [n = 317] or submitted only to natural mating [NM; n = 347]). Females from the NM group were maintained with bulls from 15 to 30 days after the first TAI. The RESYNC-treated females were resynchronized 22 days after the first TAI using 1 mg of EB on the first day of the resynchronization, similar to experiment 1. No difference was found in P/AI (NM [57.1%] vs. RESYNC [61.5%]; P = 0.32) or pregnancy loss (NM [2.0%] vs. RESYNC [4.1%]; P = 0.21) after the first TAI. Moreover, the overall P/AI after the RESYNCH protocol was 47.5%. Thus, the administration of 1 mg of EB on day 22 after the first TAI, when the pregnancy status was undetermined, promotes a higher P/AI in the resynchronized TAI than the use of GnRH. Also, the administration of 1 mg of EB 22 days after the TAI did not affect the preestablished pregnancy.     

Effect of prostaglandin F(2)alpha at insemination on sperm cell numbers and pregnancy rate in beef cattle

Fourteen cycling, nonlactating, multiparous beef cows were artificially inseminated (AI) 10 to 12 h after the onset of natural estrus. One unit of frozen-thawed semen containing 100 x 10(6) total sperm cells was deposited into the body of the uterus. Immediately after AI, alternating cows were injected i.m. with either 25 mg (5 ml) of prostaglandin F(2)alpha (PGF) or 5 ml of 0.9% saline-benzyl alcohol control solution. Cows were slaughtered 16 +/- 1 h post AI, oviducts were retrieved, segmented into thirds (upper, middle and lower) and flushed with 1 ml of 0.2% gluteraldehyde in phosphate buffered saline. The number of sperm cells was counted using a phase contrast microscope. There were no right or left side effects (P=0.61) on the number of sperm cells recovered per oviduct within cow (389 vs 553; average SEM = 219). PGF had no effect (P=0.77) on the number of sperm cells recovered per oviduct (642 vs 300; average SEM = 231 for PGF and control females, respectively). More sperm cells were recovered from the lower third segment (P<0.05) compared with the middle and upper segments. Ovulation tended to affect (P=0.10) the number of sperm cells recovered per oviduct (742 vs 200; average SEM = 231). Additionally, 114 beef females (68 Angus x Hereford heifers and 46 Chianina crossbred postpartum suckled cows) were treated as described above following AI at natural estrus with 20 x 10(6) motile sperm cells. Pregnancy rates did not differ significantly in heifers (70.6 vs 58.8%) or in Chianina cows (34.8 vs 52.2%) for control and PGF-treated females, respectively. Overall, pregnancy rates were identical between control and PGF-treated females at 56.1%. In this study, PGF treatment immediately following AI in beef cattle had no effect on the number of sperm cells in the oviducts or on the pregnancy rate.     

Influence of stage of lactation and milk production on conception rates after timed artificial insemination following Ovsynch

Conception rates after timed artificial insemination (TAI) are of paramount importance for the success of protocols based on synchronization of ovulation. Stage of lactation and milk production level are known factors that influence dairy cow fertility. It was the objective of this study to analyse the effect of stage of lactation and milk production level on conception rates and pregnancy rates by 200 days in milk (DIM) in dairy cows synchronized with the Ovsynch protocol (Day -10, Day -1: 0.1 mg of D-Phe6-gonadorelin, Day -3: 0.5 mg of cloprostenol, Day 0: AI). A total of 1,288 dairy cows were assigned to two groups and classified in three production levels (high, average, low). Cows of all milk production levels in Group 1 (Simultaneous Ovsynch, SO) were synchronized with the Ovsynch protocol simultaneously for TAI between 73 and 81 DIM. In Group 2 cows with average milk production were synchronized at the same time as Group 1, while low producing cows were synchronized 3 weeks earlier and high producing cows were synchronized 3 weeks later than Group 1, respectively. First service conception rates (FSCRs) were lower (P<0.05) in cows synchronized earlier than in cows of the same production level synchronized later (low production: 14.4% (22/153) versus 34.5% (51/148); high production: 28.2% (40/142) versus 41.4% (53/128)). Milk production level had no significant impact on conception rates after TAI in cows synchronized at the same stage of lactation. At 200 DIM fewer cows with high production level were pregnant than cows with average or low production (P<0.05). This effect was independent of the stage of lactation at the initiation of Ovsynch. Endometritis at a postpartum examination did not influence conception rates after TAI. In conclusion, stage of lactation, but not milk production level, has a major influence on conception rates after TAI. Early AI after Ovsynch is less efficient and therefore its return on investment should be evaluated carefully.     

Comparison of an oestrus synchronisation protocol with oestradiol benzoate and PGF2alpha and insemination at detected oestrus to a timed insemination protocol (Ovsynch) on reproductive performance of lactating dairy cows

A total of 226 out of 245 postpartum lactating dairy cows in a commercial dairy farm were allocated to two groups of oestrous synchronisation protocols in order to evaluate reproductive performance. One group was treated with oestradiol benzoate (ODB) and PGF2alpha on day 10 of the oestrous cycle with insemination at the detected oestrus, the second group underwent the Ovsynch (OVS) protocol (GnRH + PGF2alpha + GnRH) with timed AI. Pregnancy was diagnosed by ultrasonography on day 28 after AI and confirmed by rectal palpation on day 45. A higher (P < 0.001) proportion of cows in OVS (100%) were inseminated within (19.2 +/- 3.8 h) following the second GnRH injection than those of cows in EPE (ODB + PGF2alpha + ODB) (70.6%) inseminated at the detected oestrus within (35.6 +/- 5.2 h) following the second ODB injection. Pregnancy rates for the first AI at day 28 (64.0 +/- 4.6, 62.4 +/- 5.5%) and at day 45 post-insemination (40.4 +/- 4.7, 40.0 +/- 5.6%) for OVS and EPE cows respectively, did not differ between the two treatments, whereas, the overall pregnancy rates tended to be higher (P < 0.08) for the OVS (85.1 +/- 3.8%) cows than the EPE cows (74.1 +/- 4.5%). No differences were observed in pregnancy rates for first AI and overall up to fourth AI between primiparous (34.7 +/- 5.8 and 85.3 +/- 4.7%) and multiparous cows (43.5 +/- 4.5 and 77.4 +/- 3.6%). Days open for pregnant cows tended to be lower (P < 0.08) for OVS (76.2 +/- 3) than for EPE cows (84.7 +/- 4), while days open were higher (P < 0.05) in primiparous cows (85.3 +/- 4) than in multiparous cows (75.6 +/- 3). The results indicate that pregnancy rates for first AI were similar, but overall pregnancy rates up to the fourth AI tended to be higher for OVS than EPE cows, while days open was tended to be lower for OVS than EPE cows.     

Effect of pregnancy on oxytocin-induced release of prostaglandin F2 alpha in heifers

The effect of pregnancy on the release of prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin (OT) has been examined. Fourteen cyclic heifers received one intravenous injection of 1 IU OT (n = 6) or 100 IU OT (n = 8) 17, 18, or 19 days (Day 17-19) after the onset of estrus (Day 0). Five of these animals also received 100 IU OT at Days 6 and 13 to determine the effect of OT at different times of the cycle. Frequent blood samples were taken for 60 min before and for 90 min after OT injection for the measurement of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) by radioimmunoassay. The experiment was then repeated using the same animals at Day 17-19 of pregnancy (confirmed by the recovery of an embryo the day after OT injection). Following the injection of 1 IU OT, plasma PGFM reached its peak within 30 min with the increase significantly lower (P less than 0.05) in pregnant (1.13 +/- 0.10-fold) than in nonpregnant animals (2.07 +/- 0.27-fold). However, because only 3 of the 6 cyclic animals showed a response to 1 IU OT, the dose was increased to 100 IU in subsequent experiments. The animals that received 100 IU at Days 6 and 13 had no significant increase in PGFM concentrations (1.18 +/- 0.05-fold and 1.01 +/- 0.04-fold, respectively). At Day 17-19 the increase in plasma PGFM reached its peak 5-15 min after 100 IU OT and the increase was significantly greater in nonpregnant (3.23 +/- 0.17-fold) than in pregnant (1.21 +/- 0.02-fold; P = 0.003) heifers. Six of 11 animals injected at Day 17-19 of the cycle showed a decrease in progesterone (P4) the day after OT administration. These data show that the release of PGF2 alpha in response to OT is suppressed in pregnant animals in vivo, suggesting an antiluteolytic role for the embryo in luteostasis.     

Effect of prostaglandin F2 alpha at different stages of guinea-pig pregnancy

It is believed that suppression of the processes by which prostaglandin F2 alpha is released from the uterus during the estrous cycle is vital to maintenance of pregnancies in guinea-pigs. Prostaglandin F2 alpha was injected into pregnant guinea-pig at four different stages of gestation to investigate the effect increased prostaglandin might have. The study revealed an alteration in the sensitivity of the pregnancy to prostaglandin F2 alpha as pregnancy progressed. Recovery from the prostaglandin insult was more likely if the injection was given after Day 24 than before Day 18. In some animals the serum progesterone levels fell following the injection and then subsequently recovered. It appears that effects which are potentially hazardous to the pregnancy are countered in a variety of ways.     

Synchronization of estrus in yearling beef heifers with the melengestrol acetate/prostaglandin F(2alpha) system: efficiency of timed insemination 72 hours after prostaglandin treatment

Two experiments were conducted to determine the conception rates of heifers time-inseminated following melengestrol acetate/prostaglandin F(2alpha) (MGA/PG) estrous synchronization treatment. In Experiment 1, timed insemination of heifers at 72 h after the PG injection, without regard for behavioral estrus, tended to improve (P < 0.15) the percentage of heifers pregnant to artificial insemination (AI) compared with that of synchronized heifers bred 12 h after they were first detected in estrus. In the timed-insemination treatment, heifers exhibiting behavioral estrus 48 to 72 h after PG tended to have an increased (P < 0.15) conception rate to AI compared with heifers exhibiting estrus within 48 h of PG administration. In Experiment 2, the number of heifers conceiving to AI following the MGA/PG estrous synchronization regimen was increased by mass insemination of all heifers not exhibiting estrus by 72 h after PG. The pregnancy rate to AI was higher in heifers with serum progesterone (P(4)) concentrations higher than 1 ng/ml compared with that of heifers with concentrations lower than 1 ng/ml. Of heifers with serum P(4) greater than 1 ng/ml, the pregnancy rate to AI tended to be higher when concentrations exceeded 2 ng/ml than when concentrations were 1 to 2 ng/ml. In cyclic heifers, timed insemination can increase the percentage of heifers pregnant after being synchronized with MGA/PG.     

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.     

Effect of prostaglandin F2alpha at the time of AI on progesterone levels and pregnancy rate in synchronized Italian Mediterranean buffaloes

The aims of this study were to evaluate the effects of an intravenous or intramuscular PGF2alpha analogue administration on the day of estrus on progesterone concentration and pregnancy rate in buffaloes undergoing artificial insemination (AI). To this end, two experiments were carried out. The first study was performed on 72 Mediterranean buffaloes synchronized by the Ovsynch-TAI Program. On the day of estrus only animals considered in heat were divided into four groups: Groups IVC and IMC received, respectively, an intravenous or intramuscular injection of cloprostenol (0.524 mg), whereas control Groups IVS and IMS received the same injections of saline. Milk samples were collected daily from each animal to assess progesterone concentration in the whey by RIA method. In addition on alternate days, buffaloes underwent transrectal ultrasound analysis. The second study was carried out on 385 buffaloes synchronized by the Ovsynch-TAI Program. On the day of AI, animals were divided in four groups, as described in experiment 1. Pregnancy rate was evaluated either on day 26 or day 45 and embryonic mortality rate was recorded. Statistical analysis was performed by ANOVA and chi2 test. A higher (P<0.05) progesterone concentration was recorded on day 11 (Day 0=estrus day) in Groups IVC and IMC compared to Groups IVS and IMS (351.6+/-129.7 and 355.8+/-112.2 pg ml(-1) vs. 239.8+/-81.1 and 243.6+/-90.5 pg ml(-1), respectively). Furthermore, a larger CL was recorded on the same day in treated vs. control groups (1.25+/-0.15 and 1.27+/-0.17 cm, respectively, in Groups IVC and IMC vs. 1.08+/-0.14 and 1.05+/-0.13 cm in IVS and IMS). In the second study, a higher pregnancy rate was observed in treated (IVC+IMC) vs. control (IVS+IMS) groups (46.7% vs. 30.7%; P<0.01), while no differences were recorded between treated groups. From these data, it can be concluded that either intravenous or intramuscular administration of PGF2alpha at the time of AI can enhance progesterone levels and pregnancy rate in buffaloes.     

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.     

Effect of periovulatory prostaglandin F2alpha on pregnancy rates and luteal function in the mare.

The objective of this study was to determine whether periovulatory treatments with PGF2alpha affects the development of the CL, and whether the treatment was detrimental to the establishment of pregnancy. Reproductively sound mares were assigned randomly to one of the following treatment groups during consecutive estrus cycles: 1. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol (PGF2alpha analogue) on Days 0, 1, and 2 after ovulation (n=8), 2. 2 mL sterile water injection within 24 hours before artificial insemination and 500 microg cloprostenol on Days 0, 1, and 2 after ovulation (n=8); 3. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol on Day 2 after ovulation (n=8); or 4. 3,000 IU hCG within 24 hours before artificial insemination and 2 mL of sterile water on Days 0, 1, and 2 after ovulation (controls; n=8). Blood samples were collected from the jugular vein on Days 0, 1, 2, 5, 8, 11, and 14 after ovulation. Plasma progesterone concentrations were determined by the use of a solid phase 125I radioimmunoassay. All mares were examined for pregnancy by the use of transrectal ultrasonography at 14 days after ovulation. Mares in Group 1 and 2 had lower plasma progesterone concentrations at Day 2 and 5, compared to mares in the control group (P < 0.001). No difference was detected between group 1 and 2. Plasma progesterone concentrations in group 3 were similar to the control group until the day of treatment, but decreased after treatment and were significantly lower than the control group at Day 5 (P < 0.001). Plasma progesterone concentrations increased in all treatment groups after Day 5, and were comparable among all groups at Day 14 after ovulation. Cloprostenol treatment had a significant effect on pregnancy rates (P < 0.01). The pregnancy rate was 12.5% in Group 1, 25% in Group 2, 38% in Group 3, and 62.5% in Group 4. It was concluded that periovulatory treatment with PGF2alpha has a detrimental effect on early luteal function and pregnancy.     

Effect of sequential treatment with prostaglandin F2 alpha and/or oxytocin on estrus and pregnancy rate of lactating dairy cows

A total of 335 lactating dairy cows was used to determine the effect of oxytocin or PGF2a given 8 h after treatment with a luteolytic dosage of PGF2a on the percentage of cows exhibiting estrus within 7 d after treatment, and the pregnancy rate to a single insemination at this time. On the initial day of treatment (Day 0), cows with a palpable corpus luteum on the ovary were treated with 25 mg, im of PGF2a. At 8 h later, the cows were divided into 3 groups. Cows in Group 1 (n = 112) were treated with oxytocin (0.33 IU/kg bwt im); cows in Group 2 (n = 112) were treated with 25 mg, im of PGF2a; and cows in Group 3 (n = 111) served as the untreated controls. Cows in all 3 groups were continuously observed for estrus visually or by way of an activated heatmount detector within 7 d after treatment, and were inseminated within 12 h of the observed estrus.Plasma progesterone (P4) concentration was determined using radioimmunoassay on Day 0 and Day 2. Of the cows with P4 greater than 1 ng/ml on Day 0, the percentage of cows observed in estrus within 7 d after treatment was 75, 89 and 72% for cows in Group 1, Group 2 and Group 3, respectively. When all cows were evaluated, the percentage of cows observed in estrus within 7 d after treatment was 60, 70 and 55% for cows in Group 1, Group 2 and Group 3, respectively. In both instances, the value for cows in Group 2 was significantly higher than that for either cows in Group 1 or Group 3. The pregnancy rate for cows inseminated within 7 d was similar for cows in all 3 groups. The results of this study demonstrated that treatment of dairy cows with 2 luteolytic dosages of PGF2a at an 8-h interval resulted in more cows being observed in estrus within 7 d than with 1 treatment with PGF2a, or with oxytocin given at an 8-h interval after a luteolytic dosage of PGF2a.     

Effect of progesterone concentrations,follicle diameter,timing of artificial insemination,and ovulatory stimulus on pregnancy rate to synchronized artificial insemination in postpubertal Nellore heifers

Two experiments were designed to evaluate the effects of treatments with low versus high serum progesterone (P₄) concentrations on factors associated with pregnancy success in postpubertal Nellore heifers submitted to either conventional or fixed timed artificial insemination (FTAI). Heifers were synchronized with a new controlled internal drug release device (CIDR; 1.9 g of P₄ [CIDR1]) or a CIDR previously used for 18 days (CIDR3) plus 2 mg of estradiol (E₂) benzoate on Day 0 and 12.5 mg of prostaglandin F2α on Day 7. In experiment 1 (n = 723), CIDR were removed on Day 7 or 9 and heifers were inseminated after estrus detection. In experiment 2 (n = 1083), CIDR were all removed on Day 9 and FTAI was performed either 48 hours later in heifers that received E₂ cypionate (ECP) on Day 9 (0.5 mg; E48) or 54 or 72 hours later in conjunction with administration of GnRH (100 μg; G54 or G72). Synchronization with CIDR1 resulted in greater serum P₄ concentrations and smaller follicle diameters on Days 7 and 9 in both experiments. In experiment 1, treatment with CIDR for 9 days decreased the interval from CIDR removal to estrus (Day 7, 3.76 ± 0.08 days vs. Day 9, 2.90 ± 0.07; P < 0.01) and improved conception (Day 7, 57.1% vs. Day 9, 65.8%; P = 0.05) and pregnancy rates (Day 7, 37.6% vs. Day 9, 45.3%; P = 0.04). In experiment 2, treatment with ECP improved (P < 0.01) the proportion of heifers in estrus (E48, 40.9%^a; G54, 17.1%^c; and G72, 32.0%^b), but the pregnancy rate was not affected (P = 0.64) by treatments (E48, 38.8%; G54, 35.5%; G72, 37.5%). Synchronization with CIDR3 increased follicle diameter at FTAI (CIDR1, 11.07 ± 0.10 vs. CIDR3, 11.61 ± 0.10 mm; P < 0.01), ovulation rate (CIDR1, 82.8% vs. CIDR3, 88.0%; P < 0.01) and did not affect conception (CIDR1, 42.2 vs. CIDR3, 45.1%; P = 0.38) or pregnancy rates (CIDR1, 34.7 vs. CIDR3, 39.4%; P = 0.11). In conclusion, length of treatment with P₄ affected the fertility of heifers bred based on estrus detection. When the heifers were submitted to FTAI protocol, follicle diameter at FTAI (≤10.7 mm, 23.6%; 10.8–15.7 mm, 51.5%; ≥15.8 mm, 30.0%; P < 0.01) was the main factor that affected conception and pregnancy rates.     

Histophysiological studies of prostaglandin F2alpha on isolated organs. I. Effect of prostaglandin F2alpha on the heart.

The physiological and histochemical effects of PGF2alpha on isolated rabbit hearts were examined. The results showed a positive inotropic effect. The coronary flow increased. From the histochemical studies, adenosine triphosphatase (ATP-ase) and succinic dehydrogenase activities were increased while that of alkaline phosphatase was decreased. Glycogen granules were depleted. These findings were discussed on a histophysiological basis.     

Efficacy of the Ovsynch protocol for synchronization of ovulation and fixed-time artificial insemination in Murrah buffaloes (Bubalus bubalis)

Two experiments were conducted to assess the timing and synchrony of ovulation, plasma LH concentrations, and pregnancy rate in Murrah buffaloes (Bubalus bubalis) treated with the Ovsynch (GnRH-PGF(2 alpha)-GnRH) protocol. In Experiment 1, 10 non-lactating cycling buffaloes received 10 microg of a GnRH analogue i.m. (buserelin acetate) without regard to the stage of the estrous cycle (day of treatment, day 0), followed by 25mg of PGF(2 alpha) i.m. (dinoprost thromethamine) 7 days later. A second-treatment of the same GnRH analogue (10 microg, i.m.) was given 48 h after PGF(2 alpha). Ovulation was confirmed by transrectal palpation (at 2-h intervals) from the second-GnRH treatment to detection of ovulation or up to 96 h after the second-GnRH treatment. Plasma LH concentrations were determined in blood samples collected at 15-min intervals for 6h, starting at the second-GnRH treatment, and thereafter at 2-h intervals until 2h after detection of ovulation. Ovulation occurred in 9/10 buffalo (90%) 23.3+/-1.3h (mean+/-S.E.M.; range 20--32 h) after the second-GnRH treatment. Peak LH concentrations 13.5+/-3.5 ng/mL (range 3.9--40.0 ng/mL) occurred 2.1+/-0.1h (range 1.2-3.0 h) after the second-GnRH treatment. In Experiment 2, 15 lactating, cycling buffaloes were subjected to the Ovsynch protocol, with fixed-time AI 12 and 24h after the second-GnRH treatment and 75 lactating buffaloes were inseminated, approximately 12h after detection of spontaneous estrus. Pregnancy rates were 33.3% for TAI and were 30.7% for buffaloes inseminated following spontaneous estrus (P=0.84). In conclusion, the Ovsynch protocol effectively synchronized ovulation in Murrah buffaloes and resulted in conception rates (to two fixed-time inseminations) that were comparable to those achieved with a single AI after detection of spontaneous estrus.     

Timing of insemination and fertility in dairy and beef cattle receiving timed artificial insemination using sex-sorted sperm

The objective was to evaluate the effects of timing of insemination and type of semen in cattle subjected to timed artificial insemination (TAI). In Experiment 1, 420 cyclic Jersey heifers were bred at either 54 or 60 h after P4-device removal, using either sex-sorted (2.1 × 10⁶ sperm/straw) or non-sorted sperm (20 × 10⁶ sperm/straw) from three sires (2 × 2 factorial design). There was an interaction (P = 0.06) between time of AI and type of semen on pregnancy per AI (P/AI, at 30 to 42 d after TAI); it was greater when sex-sorted sperm (P < 0.01) was used at 60 h (31.4%; 32/102) than at 54 h (16.2%; 17/105). In contrast, altering the timing of AI did not affect conception results with non-sorted sperm (54 h = 50.5%; 51/101 versus 60 h = 51.8%; 58/112; P = 0.95). There was an effect of sire (P < 0.01) on P/AI, but no interaction between sire and time of AI (P = 0.88). In Experiment 2, 389 suckled Bos indicus beef cows were enrolled in the same treatment groups used in Experiment 1. Sex-sorted sperm resulted in lower P/AI (41.8%; 82/196; P = 0.05) than non-sorted sperm (51.8%; 100/193). In addition, there was a tendency for greater P/AI (P = 0.11) when TAI was performed 60 h (50.8%; 99/195) versus 54 h (42.8%; 83/194) after removing the progestin implant. In Experiment 3, 339 suckled B. indicus cows were randomly assigned to receive TAI with sex-sorted sperm at 36, 48, or 60 h after P4 device removal. Ultrasonographic examinations were performed twice daily in all cows to confirm ovulation. On average, ovulation occured 71.8 ± 7.8 h after P4 removal, and greater P/AI was achieved when insemination was performed closer to ovulation. The P/AI was greatest (37.9%) for TAI performed between 0 and 12 h before ovulation, whereas P/AI was significantly less for TAI performed between 12.1 and 24 h (19.4%) or >24 h (5.8%) before ovulation. In conclusion, sex-sorted sperm resulted in a lesser P/AI than non-sorted sperm following TAI. However, improvements in P/AI with delayed time of AI were possible (Experiments 1 and 3), and seemed achievable when breeding at 60 h following progestin implant removal, compared to the standard 54 h normally used in TAI protocols.     

Factors affecting conception rate after artificial insemination and pregnancy loss in lactating dairy cows

Objectives were to determine factors associated with conception rate (CR) and pregnancy loss (PL) in high producing lactating Holstein cows. In Study 1, CR was evaluated in 7633 artificial inseminations (AI) of 3161 dairy cows in two dairy farms. Pregnancy diagnosis was performed by palpation per rectum 39+/-3 days after AI. Environmental temperature was recorded at different intervals prior to and after AI. In Study 2, 1465 pregnancies from 1393 cows diagnosed at 31+/-3 days after AI by ultrasonography on three dairy farms were re-examined 14 days later to determine PL. Temperature > or =29 degrees C was considered to be heat stress (HS). Exposure to HS was defined as following: NH, no heat stress; HS1, exposure to at least 1 day of maximum temperature > or =29 degrees C and average daily maximum temperature (ADMT) <29 degrees C; and HS2, exposure to ADMT > or =29 degrees C. In Study 1, exposure of cows to HS1 and HS2 from 50 to 20 prior to AI was associated with reduced CR compared to cows not exposed to HS (28.8, 23.0, and 31.3%, respectively). Post-AI HS was not associated with CR. Cows inseminated following estrus detection or timed AI had similar CR. As the number of AI increased, CR decreased. Multiparous cows had lower CR than primiparous cows, and occurrence of milk fever and retained placenta was associated with decreased CR. In Study 2, PL was not associated with exposure to HS either prior to or after AI. Cows diagnosed with clinical mastitis experienced increased PL, but parity, number of AI, AI protocol, milk production, and days postpartum at AI were not associated with PL. In conclusion, CR was affected by HS prior to AI, parity, number of AI, and postparturient diseases, whereas PL was affected by clinical mastitis.     

Effects of indomethacin, prostaglandin E2, prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha on hatching of mouse blastocysts

The present study has been performed to investigate how PGs would participate the hatching process. Effects of indomethacin, an antagonist to PGs biosynthesis, on the hatching of mouse blastocysts were examined in vitro. Furthermore, it was studied that prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) or 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were added to the culture media with indomethacin. The hatching was inhibited by indomethacin yet the inhibition was reversible. In the groups with indomethacin and PGE2, no improvement was seen in the inhibition of hatching and the inhibition was irreversible. In the groups with indomethacin and PGF2 alpha, inhibition of hatching was improved in comparison with the group with indomethacin. In the groups with indomethacin and 6-keto-PGF1 alpha, no improvement was seen. The above results indicated that PGF2 alpha possibly had an accelerating effect on hatching and a high concentration of PGE2 would exert cytotoxic effect on blastocysts.