Decreasing the dose of equine chorionic gonadotropin does not affect ovarian or pregnancy responses of purebred taurine and crossbred beef heifers.

In this study there was evaluation of effects of different doses of equine chorionic gonadotropin (eCG: 200, 300, or 400 IU) administrated at progesterone (P4) plus estradiol-based timed AI (TAI). A total of 1080 heifers were included in the study. There was insertion of the intravaginal P4-device plus administration of 2 mg of estradiol benzoate IM. On D7, 12.5 mg of dinoprost tromethamine IM was administered and on D9, the P4 insert was removed and 0.5 mg of estradiol cypionate IM was administered. Heifers were categorized according to Reproductive Tract Status (RTS; 1-5) and were assigned to one of three treatments: 200 IU (n = 387), 300 IU (n = 357), or 400 IU (n = 336) of eCG. Estrous occurrence was evaluated at TAI 48 h later (D11). A subset of heifers (n = 213) had the largest follicle (LF) evaluated on D9 and on D11, and the formation of a new CL evaluated on D18.There was no effect of eCG treatment on LF on D11 (P = 0.79), occurrence of estrus (P = 0.92), and pregnancy at 30 days after AI (P/AI; 52.2%, 49.8%, and 51.5% for 200 IU, 300 IU, and 400 IU, respectively; P = 0.46). Regardless of the treatment, there was a greater P/AI when heifers had a functional CL, at initiation of the estrous synchronization treatment regimen. It, therefore, is efficacious to reduce the dose of eCG to 300 or 200 IU in purebred taurine and crossbred beef heifers without negative effects on ovarian, estrous or pregnancy responses.

Estrus resynchronization in ewes with unknown pregnancy status.

Although fixed-time artificial insemination (FTAI) protocols are available for sheep, estrus resynchronization has not been previously reported. The objectives of this study were to evaluate the effect of estrus resynchronization with exogenous progestogen on endogenous progesterone levels and to compare pregnancy rates after two consecutive estrus synchronizations in ewes. In Experiment 1, ewes (n = 20) received an intravaginal device (IVD) containing 60 mg medroxyprogesterone acetate (MPA) for 10 days. At the IVD withdrawal (D0), ewes received 250 IU eCG and were allocated into two treatments: either no further treatment (Control; n = 10) or estrus resynchronization (Resynch; n = 10) from D12 to D19. Serum progesterone (P4) levels did not differ at D12 and D19 (P > 0.05), but were greater at D15 for the Control compared with the Resynch group (P < 0.05). In experiment 2, ewes (n = 250) were submitted to a first synchronization protocol followed by estrus detection and either artificial insemination (AI) or natural mating (NM). Subsequently, ewes were divided into two groups: Control (n = 104): which received no further treatment and were bred by NM; and Resynch (n = 146): which were submitted to a second synchronization starting on D14 (first IVD withdrawal = D0) and to NM after second IVD withdrawal (D20). Cumulative pregnancy rates did not differ between the Control (67.3%, 70/104) and Resynch (62.3%, 91/146) groups. In a third experiment, ewes (n = 83) were bred by two consecutive FTAI within a 20-day interval. Pregnancy rates after the first (30.1%, 25/83) and the second FTAI (36.2%, 21/58) did not differ (P > 0.05). In conclusion, although exogenous progestogen supplementation reduced circulating levels of P4, pregnancy maintenance was unaffected. Estrus resynchronization in ewes is feasible, resulting in similar fertility after the first and the second services. The use of resynchronization coupled with artificial insemination using semen from genetically superior rams may potentially accelerate genetic improvement in sheep herds by allowing a higher differential selection compared with natural breeding.

Supplementation with sunflower seed increases circulating cholesterol concentrations and potentially impacts on the pregnancy rates in Bos indicus beef cattle.

We aimed to evaluate the effect of supplementation with sunflower seed on blood concentrations of progesterone and cholesterol and on the pregnancy rate in beef cattle subjected to timed artificial insemination (TAI) and timed embryo transfer (TET). In experiment 1, cows were received 22-day supplements containing (sunflower, n = 66) sunflower seed or not (control, n = 67) immediately after a progesterone/estradiol-based TAI protocol (Day 0). The cholesterol concentration on Day 21 and the pregnancy rate were greater (P < 0.03) in the sunflower group (148.2 ± 6.1 mg/dL and 66.7%) than those in the control group (116.0 ± 6.4 mg/dL and 47.8%). In experiment 2, heifers received an in vitro-produced embryo 7 days after the expected time of the synchronized ovulation. Heifers were separated into two supplementation groups (sunflower, n = 106 and control, n = 111) for 22 days. The plasma progesterone concentration on Day 7 was not different between the groups. However, on Day 19, the plasma progesterone concentration was greater (P < 0.0001) in the sunflower group (5.8 ± 0.4 ng/mL) than that in the control group (3.5 ± 0.4 ng/mL). A greater (P < 0.05) cholesterol concentration was observed in the sunflower group than that in the control group on Days 7 (306.0 ± 11.6 vs. 277.1 ± 11.9 mg/dL, respectively) and 19 (260.5 ± 8.0 vs. 232.0 ± 8.0 mg/dL, respectively). The pregnancy rate was greater (P = 0.01) in the sunflower-treated heifers (55.7%) than that in control-treated heifers (36.9%). Results indicate that sunflower seed supplementation increases the circulating cholesterol concentrations and potentially impacts the pregnancy rate in suckled beef cattle subjected to TAI or TET.

The interval between the emergence of pharmacologically synchronized ovarian follicular waves and ovum pickup does not significantly affect in vitro embryo production in Bos indicus, Bos taurus, and Bubalus bubalis.

The aim of the present study was to determine the optimal phase of the follicular wave to perform ovum pickup (OPU) for in vitro embryo production (IVEP) in various genetic groups. For this purpose, 27 heifers-nine Bos taurus (Holstein), nine Bos indicus (Nelore), and nine Bubalus bubalis (Mediterranean)-were maintained under the same nutritional, management, and environmental conditions. Heifers within each genetic group were submitted to six consecutive OPU trials with 14-day intersession intervals, at three different phases of the pharmacologically synchronized follicular wave (Day 1, 3, or 5 after follicular wave emergence), in a 3 × 3 crossover design. When OPU was performed at different phases of the pharmacologically synchronized follicular wave (Day 1, 3, or 5), no differences were found in the percent of oocytes recovered (70.5 ± 3.1%, 75.0 ± 3.1%, 76.0 ± 3.2%, respectively; P = 0.41) or blastocyst production rates (19.4 ± 2.9%, 16.6 ± 2.9%, 15.9 ± 2.6%, respectively; P = 0.36). Comparing genetic groups, B indicus showed a higher blastocyst rate (28.3(a) ± 2.8%; P < 0.01) than B taurus and B bubalis (14.1(b) ± 2.9% and 10.2(b) ± 2.0%, respectively). However, only B indicus heifers showed a variation in the number of visualized follicles and the total and viable oocytes along consecutive OPU sessions. In conclusion, different phases of the pharmacologically synchronized ovarian follicular wave did not affect OPU-IVEP in B indicus, B taurus, and B bubalis heifers. Additionally, B indicus heifers showed greater OPU-IVEP efficiency than did the other genetic groups, under the same management conditions.

Timed artificial insemination early in the breeding season improves the reproductive performance of suckled beef cows.

The objective was to compare reproductive performance of breeding programs that used natural service (NS), AI after estrus detection (ED), and timed AI (TAI). In experiment 1, 597 suckled beef cows were randomly allocated to one of four groups. Cows in the TAI+NS group (N = 150) were bred by TAI at 11 days after the onset of the breeding season (BS). Bulls were placed with cows 10 days after TAI and remained together until the end of the 90-day BS. Cows in the TAI+ED+NS group (N = 148) received TAI, then AI based on ED for the next 45 days, and finally NS for the last 45 days of the BS. Cows in the ED+NS group (N = 147) received AI based on ED during the first 45 days of the BS, followed by NS for the last 45 days of the BS. Cows in the NS group (N = 149) were bred by NS for the entire 90-day BS. Cows in the ED+NS or NS groups had a decreased (P < 0.001) hazard of pregnancy compared with cows in the two groups bred by TAI at the onset of BS. Also, cows bred by TAI (TAI+NS = 92.7%; and TAI+ED+NS = 91.9%) had higher (P < 0.01) pregnancy rates at the end of the BS compared with cows not bred by TAI (ED+NS = 85.0%; NS = 83.2%). In experiment 2, 507 suckled beef cows were randomly assigned to one of two groups at the onset of a 90-day BS. The NS group (N = 255) received only NS during the entire BS, and the TAI+NS group (N = 252) received TAI at the onset of the BS, followed by NS until the end of BS. Cows in the TAI+NS group had 63% higher hazard of pregnancy (P < 0.001) compared with cows in the NS group, and reduced the median days to pregnancy by 44 (11 vs. 55 days). However, there was no difference (P = 0.31) in proportion of pregnant cows at the end of the BS (TAI+NS = 77.0% vs. NS = 71.0%). Therefore, incorporation of TAI programs early in the BS increased reproductive performance of suckled beef cows.

Bovine embryo transfer recipient synchronisation and management in tropical environments.

Numerous studies have shown that it is possible to manipulate follicular and luteal dynamics, thereby eliminating the need for oestrus detection in embryo transfer (ET) programmes. Fixed-time ET (FTET) protocols are based on the use of gonadotrophin-releasing hormone (GnRH) and prostaglandin (PG) F or progesterone/progestogen (P4)-releasing devices and oestradiol. The FTET protocols increases the proportion of recipients transferred, and therefore pregnancy rates, compared with the use of PGF followed by ET 7 days after oestrus. Furthermore, the addition of equine chorionic gonadotrophin (eCG) to the P4 and oestradiol-based FTET protocols results in an even higher proportion of recipients transferred, and thus higher pregnancy rates. The beneficial effect of eCG treatment may be related to increased growth of the dominant follicle and increased plasma P4 concentrations during the subsequent luteal phase. In Bos taurus x Bos indicus recipients, pregnancy rates were positively correlated with the diameter of the corpus luteum (CL) and the number of CL at ET. When repeat-breeder Holstein cows were used as recipients, FTET protocols increased number of recipients transferred and pregnancy rates compared with the traditional PGF-based synchronisation protocols. In conclusion, the use of FTET protocols eliminates the need for the detection of oestrus and results in a greater proportion of recipients transferred and satisfactory pregnancy rates. Thus, FTET optimises the use of recipients, reducing labour and animal handling and facilitating the use of ET.

Superovulation and embryo transfer in Bos indicus cattle.

Compared to Bos taurus breeds, Bos indicus breeds of cattle present several differences in reproductive physiology. Follicular diameter at deviation and at the time of ovulatory capability are smaller in B. indicus breeds. Furthermore, B. indicus breeds have a greater sensitivity to gonadotropins, a shorter duration of estrus, and more often express estrus during the night. These differences must be considered when setting up embryo transfer programs for B. indicus cattle. In recent studies, we evaluated follicular dynamics and superovulatory responses in B. indicus donors with the objective of implementing fixed-time AI protocols in superstimulated donors. Protocols using estradiol and progesterone/progestrogen releasing devices to control follicular wave emergence were as efficacious as in B. taurus cattle, allowing the initiation of superstimulatory treatments (with lower dosages of FSH than in B. taurus donors) at a self-appointed time. Furthermore, results presented herein indicate that delaying the removal of progesterone/progestogen-releasing devices, combined with the administration of GnRH or pLH 12 h after the last FSH injection, results in synchronous ovulations, permitting the application of fixed-time AI of donors without the necessity of estrus detection and without compromising the results.