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1.
Two estrous synchronization protocols were used to determine their effect on estrous characteristics, synchronization rates, and pregnancy rates in nulliparous beef heifers on a commercial cow-calf operation in western New Mexico. Fifty-three Red Angus and Angus × Hereford heifers were sorted by age and BW to compare heifers treated with gonadotropin-releasing hormone (GnRH) 7 d before treatment with prostaglandin F2α [PGF2α; SelectSynch (SS); n = 26] and heifers treated with two administrations of PGF2α 14 d apart [Targeted Breeding™ (TB) (Pharmacia, Kalamazoo, MI); n = 27). An androgenized cow fitted with a chin-ball marker was placed in each pen of heifers, and a HeatWatch (HW) transmitter (DDx, Inc., Denver, CO) was attached to each heifer to monitor estrous characteristics. Heifers were artificially inseminated after estrus was determined by HW. Number of standing events tended (P=0.12) to increase for TB heifers compared with SS heifers (54.4 ± 7.4 and 37.5 ± 7.7, respectively). Duration of estrus was increased (P<0.05) in TB heifers (16.0 ± 1.3 h) compared with SS heifers (11.6 ± 1.3 h). However, overall synchronization and pregnancy rates were similar (P>0.10) between protocols. Androgenized cows identified 53% of the estruses detected by HW. When utilizing synchronization protocols, radiotelemetric estrous detection systems may identify more heifers in estrus than androgenized cows. Intensity of estrus was increased in TB heifers compared with SS heifers; however, synchronization and pregnancy rates were not influenced by synchronization protocol.  相似文献   

2.
Objectives of this study were to evaluate synchronization, conception, and pregnancy rates of heifers synchronized with melengestrol acetate (MGA)-prostaglandin F2α (PGF2α,), Select Synch, or Select Synch preceded by MGA (MGA-Select Synch). Heifers in the MGA-PGF2α group (n = 209; BW = 378 kg) received MGA (0.5 mg/ d per heifer) for 14 d and PGF2α (25 mg) 19 d later. Select Synch heifers (n = 213; BW = 374 kg) received gonadotropin-releasing hormone (GnRH; 100 μg) followed by PGF2α (25 mg) 7 d later. The MGA-Select Synch heifers (n = 210; BW = 373 kg) were fed MGA (0.5 mg/d per heifer) for 7 d, GnRH (100 μg) the day following the last MGA feeding, and PGF2α (25 mg) 7 d after GnRH. More (P<0.01) heifers were in estrus 1 to 4 d before PGF2a administration in both the Select Synch (20%) and MGA-Select Synch (24%) groups than in the MGA-PGF2α (4%) group. Pregnancy rates for heifers in estrus early (d 1 to 4 before PGF2α) were greater (P<0.05) for both Select Synch (55%) and MGA-Select Synch (63%) compared with MGA-PGF2α heifers (18%). Synchronization rate (detected after PGF2α) was greater (P<0.01) for MGA-PGF2α heifers (86%) compared with Select Synch (66%) and MGA-Select Synch (68%) heifers; however, conception rate did not differ (P=0.13) and averaged 72, 63, and 62% for MGA-PGF2α, Select Synch, and MGA-Select Synch heifers, respectively. Select Synch (52%), MGA-Select Synch (58%), and MGA-PGF2α protocols (61%) provided similar (P=0.18) overall AI pregnancy rates; however, more heifers were in estrus before PGF2α administration in protocols using GnRH.  相似文献   

3.
At the beginning of the breeding season, most beef herds consist of a population of cyclic and anestrous postpartum cows. To be most effective and economical, an estrous synchronization method for postpartum beef cows must be capable of synchronizing estrus in cyclic cows and inducing estrus in anestrous cows. In the first of two experiments, the combination of melengestrol acetate (MGA) fed for 9 d and prostaglandin F2 alpha (PGF2 alpha) administered on the last day of MGA feeding synchronized estrus in cyclic cows (94%) and induced estrus in anestrous cows (66%) as effectively as combining PGF2 alpha with a progestin implant (97 and 75%, respectively). In the second experiment, MGA treatment was necessary for 7 d prior to administering PGF2 alpha to maximize the expression of estrus in cyclic and anestrous cows. In both experiments the proportion of cows exhibiting a synchronized estrus and the pregnancy rates tended to be higher for cows that were cyclic prior to treatment. However, the MGA-PGF2 alpha treatments consistently induced estrus in more than 50% of the anestrous cows and approximately one-third of the cows that were anestrous prior to treatment conceived during the synchronized breeding period. The MGA-PGF2 alpha treatment was 33 to 46% less expensive than a comparable estrous synchronization method that is approved by the U.S. Food and Drug Administration. If feeding MGA and administering PGF2 alpha is approved, it may be the treatment of choice for synchronizing estrus in cyclic cows and inducing estrus in anestrous cows when supplemental feeding is feasible.  相似文献   

4.
Estrous expressions in dairy cows have been shortened and weakened. Dairy heifers, on the other hand, may not have had such changes in estrous signs as observed in cows, since they have less stresses than cows. The aim of this study was to describe the duration of estrus in a herd of dairy heifers. A total of 56 Holstein Friesian heifers estrus was synchronized using two different hormonal protocols. They were checked for primary and secondary estrous signs with the help of heat detection devices for 48 h at an interval of 4 h starting at 16.00 hour, one day after PGF2α treatment. Onset and end of standing estrus during 48 h observation period was recorded in 35 of the 44 heifers coming into estrus within 5 days after PGF2α treatment during the observation period. The duration of standing estrus on the average (±SD) was 9.7 ± 5.3 h. Percentage of heifers with standing estrus longer than 12 h was 40%, and 53% showed standing estrus only for 4–8 h. It is indicated that duration of estrus in dairy heifers has been shortened recently.  相似文献   

5.
This study was designed to determine if prostaglandin F2α (PGF2α) when administered on d 6 post-ovulation in a low dose in the lumbosacral space (LSS) would induce luteolysis while minimizing side effects usually associated with intramuscular administration of this analogue in mares. A second objective was to determine if human chorionic gonadotropin (hCG) injected into the LSS would reduce time to ovulation in the mare. Ten normally cycling mares served as their own controls in a crossover design, receiving intramuscular injections of PGF2α(10 mg), intravenous injections of hCG (3000 IU) and injections of PGF and hCG at the acupuncture site (2 mg and 3000 IU, respectively), as well as sham injections of saline. Beginning 12 h after injection, mean progesterone concentrations were less (P<0.05) in PGF2α-treated mares than in mares receiving saline. Moreover, progesterone concentrations were similar (P<0.001) between both groups of mares receiving PGF2α. In addition, there was no difference (P>0.1) between mares receiving the acupuncture injection of PGF2α and the intramuscular injection in days to ovulation. However, duration and severity of side effects associated with PGF2α administration were dramatically decreased (P<0.01) when PGF2α was delivered to the acupuncture site compared to intramuscular delivery. The time to ovulation was similar (P>0.1) for mares receiving shams, or hCG. These data indicate that delivery of 2 mg of PGF2α in the LSS induces luteolysis and reduces the sweating and muscle cramping associated with PGF2α administration. There was no advantage to the delivery of hCG in the LSS.  相似文献   

6.
The objective was to determine the effects of duration of progestin exposure prior to gonadotropin treatment on the synchronization of estrus and fertility in gilts. Gilts were fed daily a complete diet containing 15 mg Regu-mate® (Intervet America Inc., Millsboro, DE) for 14 (n = 19) or 18 (n = 18) d. Twenty-four hours after the last feeding of Regu-mate®, all gilts received an i.m. injection of P.G. 600® [400IU pregnant mare serum gonadotropin (PMSG) and 200 IU human chorionic gonadotropin (hCG); Intervet America Inc.]. Gilts were bred artificially 12 and 24 h after first detection of standing estrus. More 18-d (33.3%) than 14-d treated gilts (5.3%) were in estrus on the peak day (d 4.0) after P.G. 600® injection (P=0.02). The percentage of gilts displaying estrus < 7 d after P. G. 600® injection was greater (P=0.06) for the 18-d treatment (88.9%) than for the 14-d treatment (63.2%). Farrowing rate tended to be greater (P=0.17) for gilts exposed to Regu-mate® for 18 d (75%) compared with 14 d (50%). Total pigs born (P=0.43), pigs born live (P=0.63), stillborns (P=0.62), and total litter weight (P=0.52) were similar between groups. The number of mummified fetuses tended to be higher (P=0.11) for gilts in the 18-d treatment group (0.8 ± 0.2) compared with the 14-d treatment group (0.2 ± 0.3). In summary, the precision of estrus synchronization and reproduction was greater in gilts given P.G. 600® after 18 d compared with 14-d Regu-mate® treatment.  相似文献   

7.
Although prostaglandin (PG) F2α analogues are routinely used for oestrus synchronisation in cattle, their effects on the function of the bovine corpus luteum (CL), and on ovarian arterial contractility, may not reflect the physiological effects of endogenous PGF2α. In the first of two related experiments, the effects of different analogues of PGF2α (aPGF2α) on the secretory function and apoptosis of cultured bovine cells of the CL were assessed. Enzymatically-isolated bovine luteal cells (from between days 8 and 12 of the oestrous cycle), were stimulated for 24 h with naturally-occurring PGF2α or aPGF2α (dinoprost, cloprostenol or luprostiol). Secretion of progesterone (P4) was determined and cellular [Ca2+]i mobilisation, as well as cell viability and apoptosis were measured.Naturally-occurring PGF2α and dinoprost stimulated P4 secretion (P < 0.05), whereas cloprostenol and luprostiol did not influence P4 synthesis. The greatest cytotoxic and pro-apoptotic effects were observed in the luprostiol-treated cells, at 37.3% and 202%, respectively (P < 0.001). The greatest effect on [Ca2+]i mobilisation in luteal cells was observed post-luprostiol treatment (200%; P < 0.001).In a second experiment, the influence of naturally-occurring PGF2α and aPGF2α on ovarian arterial contraction in vitro, were examined. No differences in the effects of dinoprost or naturally-occurring PGF2α were found across the studied parameters. The effects of cloprostenol and luprostiol on luteal cell death, in addition to their effects on ovarian arterial contractility, were much greater than those produced by treatment with naturally-occurring PGF2α.  相似文献   

8.
The objective of this study was to evaluate synchronization and pregnancy rates of beef heifers supplemented with 0.91 kg of whole sunflower seeds for 0, 30, or 60 d before AI. Beef heifers from four locations (n = 1,014) were assigned by BW to treatment (within location) and randomly to AI sire. Heifers at Location 1 (n = 176; mean BW = 332 kg) received either 0- or 60-d sunflower seed treatments. Heifers at Location 2 (n = 397; mean BW = 334 kg) were fed sunflower seeds for 0, 30, or 60 d. Heifers at Locations 3 (n = 211; mean BW = 345 kg) and 4 (n = 230; mean BW = 343 kg) received 0- or 30-d sunflower seed treatments. Within location, diets were formulated to be isocaloric and isonitrogenous. All heifers received melengesterol acetate (0.5 mg/d per head) for 14 d followed 19 d later by an injection of prostaglandin F2a (PGF) (25 mg). Heifers were bred by AI according to the AM/PM rule except on d 3 when all heifers that had not exhibited estrus were artificially inseminated in mass. Neither 72-h estrous response nor pregnancy rate was affected (P>0.10) by 30- or 60-d sunflower feeding. In summary, feeding 0.91 kg of whole sunflower seeds for either 30 or 60 d before AI did not improve estrous response or pregnancy rate when compared with controls.  相似文献   

9.
The effect of the uterus on luteal lifespan and pattern of secretion of progesterone following early weaning of calves from anestrous beef cows was studied. Calves were weaned from 15 anestrous beef cows 23 to 33 d postpartum, and cows were allotted to a control (sham surgery, n = 8) or a hysterectomy (n = 7) group, with surgery performed at weaning. Cows in the hysterectomy group were injected (im) with 25 mg prostaglandin F2 alpha (PGF2 alpha) approximately 20 d after first estrus (d 0). The interval from weaning to estrus was longer (P less than .05) for the hysterectomy group (10.4 +/- 1.6 d) than the control group (6.2 +/- .5 d). In the control group, the first estrous cycle (8.8 +/- .3 d) was shorter (P less than .01) than the second estrous cycle (20.2 +/- .5 d). Following first estrus in the hysterectomy group, cows were not detected in estrus until after injection of PGF2 alpha and did not return to estrus. From d 0 to 5, mean concentrations of plasma progesterone were similar (P greater than .05) between groups for both estrous cycles; after d 5 of estrous cycle 1, concentrations of plasma progesterone decreased in the control group. Within the hysterectomy group, the pattern of secretion of progesterone from d 0 to 16 was similar after the first and second estrus. Furthermore, there was no difference in the pattern of secretion of progesterone from d 0 to 16 between hysterectomy (first or second estrous cycles) and control (second estrous cycle) groups.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

10.
Two experiments were conducted to determine whether extending the interval between removal of melengestrol acetate (MGA) from feed and injection of prostaglandin F2α (PGF) from 17 to 19 d would affect synchronization of estrus, conception, and pregnancy rates of beef heifers. In both experiments, heifers were fed MGA for 14 d, and PGF was given at either 17 or 19 d after cessation of MGA feeding. Heifers were observed for estrus and artificially inseminated for 5 d after PGF injection. In Exp. 1, 240 yearling heifers were randomly assigned to either a 17- or a 19-d treatment group according to estrous status and day of the estrous cycle. In Exp. 2, 1409 yearling heifers on a cooperating ranch were randomly assigned to the same two treatment groups without knowledge of estrous status. The PGF injection at 19 d (Exp. 1) caused a higher (P<0.05) percentage of heifers to exhibit estrus by 72 h after the injection compared with heifers receiving the injection at 17 d. A greater percentage (P<0.01) of heifers in the 19-d group were in the late luteal phase of the estrous cycle at the time of PGF injection compared with the heifers in the 17-d group, and pregnancy rates were higher for the heifers in the late luteal phase. In Exp. 2, heifers injected with PGF at 19 d after MGA had a greater (P<0.05) percentage in estrus (10%) during the 5-d breeding period, and had higher (P<0.05) pregnancy rates in 5 d (7.6%) and 50 d of breeding (5.5%), compared with heifers injected with PGF 17 d after withdrawal of MGA. These results indicate that the PGF injection given at 19 d after removal of MGA from the diet increases synchronized estrous response and results in higher pregnancy rates in heifers compared with the 17-d injection treatment.  相似文献   

11.
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12.
When European Union regulations restricted the use of estrogenic compounds in food‐producing animals, refined hormonal protocols were no longer applicable for anovulatory cows. However, Ovsynch and its adaptations are routinely and uniformly applied to all cows regardless of ovarian function. To evaluate their efficacy on anovulatory cows, 143, 147 and 144 anovulatory cows received Ovsynch, Presynch and G6G protocols, respectively. In comparison, 150 cyclic cows were bred without using a synchronized protocol. Results showed that cows in the Presynch group had luteolysis responding to the last prostaglandin F2α (PGF2α) injection greater than the Ovsynch group. The serous progesterone levels at the first gonadotropin‐releasing hormone of Ovsych and the last PGF2α injection was greater in the G6G group than the other two hormonal treatment groups. Concentrations of Ca2+ and total protein in cervical mucus in all three hormone‐treated groups before artificial insemination (AI) were significantly different from the controls. The G6G group obtained a greater pregnancy rate compared with Ovsynch and Presynch, but significantly less than the controls. For open cows in the Ovsynch group, estrus rate within 24 days after the first AI was significantly less than the controls. In conclusion, the G6G treatment resulted to better reproductive performance in anovulatory cows.  相似文献   

13.
A 2-yr study was conducted using 82 lactating, 2-yr-old, primiparous crossbred beef cows (yr 1, n = 40; yr 2, n = 42) to study the effect of fishmeal supplementation on reproductive performance. Cows were fed a corn silage-based diet supplemented with fishmeal (5% DM) or corn gluten meal (8.7% DM), beginning 25 d prior to the start of and continuing through the 90-d breeding season. Cows were artificially bred with semen from bulls of proven fertility 12 h after being detected in estrus. Jugular blood samples were taken from all cows on d 3 or 4, 9 or 10, and 15 or 16 following first insemination and analyzed for serum progesterone. During yr 2 of the study, additional blood samples were collected from four cows within each treatment group immediately before supplementation began (d 0) and at 7-d intervals for the first 35 d of supplementation. Plasma samples were analyzed for Ω-3 fatty acids. Serum progesterone concentrations did not differ between treatment groups following the first insemination (P>0.76). However, first service conception rates approached significance (NS; P=0.12) and tended to be greater for cows supplemented with fishmeal when compared with cows supplemented with corn gluten meal (76% vs 62%, respectively). Overall pregnancy rates at the end of the breeding season did not differ between the two treatment groups (P>0.64). In yr 2, within 7 d of supplementation, plasma eicosapentaenoate (EPA) and docosahexaenoate (DHA) were greater for cows supplemented with fishmeal (P<0.001). In conclusion, these data indicate that fishmeal supplementation alters plasma EPA and DHA (yr 2) and may improve first service conception rates in primiparous beef cows.  相似文献   

14.
Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.  相似文献   

15.
Crossbred cows (n = 1073) from five locations had oestrous cycles synchronized with 100 μg of GnRH IM and insertion of controlled internal drug release device (CIDR) on Day 0 followed by 25 mg of PGF2α IM and CIDR removal on Day 7. Kamar® patches were placed on all cows at CIDR removal. Cows were observed three times daily for oestrus after PGF2α administration. In the Ovsynch‐CIDR group, cows detected in oestrus (n = 193) within 48 h after PGF2α were inseminated using the AM–PM rule. Among these cows, 80 received and 113 did not receive a second GnRH at 48 h after PGF2α. Cows (n = 345) not detected in oestrus received a second GnRH at 48 h after PGF2α on Day 9, and fixed‐time AI 16 h after the GnRH on Day 10. In the CO‐Synch‐CIDR group, cows detected in oestrus (n = 224) within 48 h after PGF2α were inseminated using the AM–PM rule. Among these cows, 79 received and 145 did not receive a second GnRH at 64 h after PGF2α. Cows (n = 311) not detected in oestrus received a second GnRH on Day 10 at the time of AI, 64 h after PGF2α. The AI pregnancy rates were not different between the Ovsynch‐CIDR and CO‐Synch‐CIDR groups (p = 0.48). There were no differences in the AI pregnancy rates for cows inseminated at a fixed time (p = 0.26) or at detected oestrus (p = 0.79) between the treatment groups. Among cows inseminated in oestrus, there were no differences in the AI pregnancy rates between cows that received or did not receive the second GnRH (p = 0.47). In conclusion, acceptable AI pregnancy rates can be achieved with or without inclusion of oestrus detection in the Ovsynch‐CIDR and CO‐Synch‐CIDR protocols. Among cows detected in oestrus, cows that received a second GnRH yielded similar pregnancy rates when compared with cows that did not receive the second GnRH.  相似文献   

16.
A study was conducted to investigate whether ovulation in gilts could be synchronized for embryo collection by the administration of estradiol benzoate (EB) or estradiol dipropionate (EDP) to induce pseudopregnancy, followed by the treatment with prostaglandin F2α (PGF2α) on 10 days after. Ten gilts each received a total of 20 mg of EB or EDP on Day 10 or EB on Day 10 and 14 to induce pseudopregnancy (Day 0 = onset of estrus). Donors received PGF2α 10 or 15 days (as a control) after the first administration of estrogens and subsequently eCG and hCG, and were then inseminated artificially. The embryos were collected 7 days after the administration of hCG, and assessed for embryo yield and their developmental stages. All protocols resulted in good embryo yield (9.8–13.2 embryos in average), and the embryos showed average ability to develop to the expanded blastocyst stage (3.29–4.03 as developmental scores) without any significant differences among the protocols. These results suggest that the administration of PGF2α 10 days after the treatment of gilts with EB or EDP would allow synchronization of ovulation and embryo collection, as well as shortening the period from estrus detection to embryo collection, thus improving embryo collection efficiency.  相似文献   

17.
The objectives were to investigate the relationships between endometrial cytology (EC) and interval from calving to first ovulation, and pregnancy in dairy cows, and that between uterine fluid and EC. On day 25 postpartum, 39 dairy cows were grouped based on EC, as having low (⩽8%) or high (>8%) polymorphonuclear cells (PMN), and the quantity of uterine fluid was assessed by ultrasound. The interval from calving to first ovulation was shorter in low, than in high PMN cows (32 vs. 45 d). A greater proportion of cows with uterine fluid had high PMN (64% vs. 21%), and the PMN increased from 14% to 34% as the quantity of uterine fluid increased. The mean interval from calving to ovulation was longer in primiparous cows with high PMN (49 d) compared to that of primiparous and multiparous cows with low PMN (28 and 29 d, respectively). Although the conception rate to first service at 92 d postpartum was not different between PMN groups, the cumulative pregnancy at 270 d tended to be higher in low than in high PMN (80% vs. 58%) multiparous cows. Also, cows that had uterine fluid on day 25 postpartum had a shorter interval from calving to pregnancy than those with no uterine fluid (161 vs. 208 d). In conclusion, combining transrectal ultrasonography with endometrial cytology on day 25 postpartum has diagnostic value in the assessment of uterine inflammation.  相似文献   

18.
Postpartum anestrous interval in beef cows is a major factor contributing to reproductive failure during a defined breeding season. Our objectives were to determine the ability of a controlled internal drug-releasing device (CIDR, 1.9 g of progesterone), a normal dose of melengestrol acetate (MGA, 0.5 mg x cow(-1) x d(-1)), or a high dose of MGA (4.0 mg x cow(-1) x d(-1)) to induce ovulation and to eliminate short estrous cycles. Multiparous beef cows (n = 100) were equally assigned to one of four treatments: CIDR, normal MGA, high MGA, or control by age, days postpartum, body condition, and body weight. All cows were fed carrier (0.9072 kg x cow(-1) x d(-1)) with (normal MGA, 0.55 mg/kg; high MGA, 4.41 mg/kg) or without MGA for 7 d (d -6 to 0). On d -6, CIDR were inserted and then removed on d 0. Estrous behavior was monitored continuously from d -6 until 29 using HeatWatch electronic mount detectors. Blood was collected on d -13, and three times weekly from d -6 to 29. Treatment influenced (P = 0.03) the percentage of cows that were detected in standing estrus. Beginning on d 2, more CIDR-treated cows had exhibited standing estrus compared with high MGA-treated or control cows, but CIDR- and normal MGA-treated cows did not differ. The percentage of CIDR-treated cows that had ovulated was greater (P < 0.05) than the percentage of normal MGA-treated, high MGA-treated, or control cows beginning on d 4. The percentage of cows that exhibited standing estrus before the first postpartum ovulation (CIDR = 65%, normal MGA = 57%, high MGA = 35%, control = 30%) did not differ (P = 0.09) among treatments. Luteal life span following the first ovulation postpartum and the percentage of cows with a normal luteal life span (i.e., progesterone > 1 ng/mL for > or = 10 d) was greater (P < 0.01) in CIDR-treated cows (14.0 +/- 0.8 d; 20/20, 100%) compared with normal MGA-treated (6.2 +/- 1.0 d; 3/13, 23%), high MGA-treated (9.6 +/- 1.0 d; 8/14, 57%), or control cows (6.1 +/- 0.9 d; 4/17, 24%), and greater (P < 0.03) in high MGA-treated cows than in normal MGA-treated or control cows. In the present study, treatment of early postpartum suckled beef cows with CIDR induced ovulation and initiated estrous cycles with a normal luteal life span in more cows than did treatment with MGA. Treatment with MGA (normal or high dose) did not induce ovulation earlier than in control cows, but a high dose of MGA increased the percentage of cows with normal luteal life spans following the first ovulation postpartum.  相似文献   

19.
The effect of bull exposure on the resumption of estrous activity following parturition was studied in an experiment using mature Hereford and Hereford X Angus beef cows. In the spring of 1981 and 1982, cows were assigned by breed and calving date to one of two treatment groups. Cows were exposed to bulls either from 3 to 85 d postpartum (BE; n = 45, 1981; n = 35, 1982) or from 53 to 85 d postpartum (NE; n = 39, 1981, n = 36, 1982). Blood samples were collected from all cows once weekly from calving until 85 d postpartum to determine progesterone concentrations. The first increase in progesterone, which indicated onset of estrous cycles occurred at 43 +/- 2 vs 63 +/- 2 d (P less than .01) in 1981 and at 39 +/- 2 vs 61 +/- 3 d (P less than .01) postpartum in 1982 in BE cows and NE cows, respectively. Early postpartum exposure of cows to bulls reduced the postpartum anestrous interval.  相似文献   

20.
A trial was conducted during the anestrous period in female goats to determine: (a) whether estrus can be induced in anestrous goats by administration of equine chorionic gonadotropic hormone (eCG) and PGF2α under pen conditions and (b) whether these sexually active female goats can elicit sexual arousal in sexually inactive bucks. One hundred and fifteen pluriparous, nonlactating mixed-breed female goats were randomly assigned to one of four treatment groups: (1) administration of a single dose of 240 IU of eCG, 50 μg PGF2α i.m., and 25 mg progesterone (P4) (eCG; n?=?30); (2) administration of P4 and exposure to female goats treated with eCG–PGF2α (P4; n?=?39); (3) administration of 0.5 ml saline and P4 (Sal; n?=?23); and (4) P4 plus exposure to female goats treated with saline (Con; n?=?23). After hormone administration, all goats were put together with adult sexually inactive bucks for 15 days. The percentage of goats in estrus during these 15 days was similar in eCG-treated animals and untreated animals exposed to the eCG animals (97 and 95 %). Pregnancy rate was also similar (63 vs. 64 %) between these two groups. eCG-treated goats exhibited estrus earlier (P?<?0.05) than the treated goats in contact with the eCG goats. Furthermore, eCG-treated goats had larger litters (1.9?±?0.2 vs. 1.6?±?0.1, P?<?0.05) than the untreated goats in contact with the eCG goats. These results show that fertile estrus can be induced in anestrous female goats by exposing them to female goats induced to estrus with eCG. This female–female interaction triggers the stimulation cycle leading to the sexual arousal of bucks.  相似文献   

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