Hepatic mRNA expression of enzymes associated with progesterone metabolism and its impact on ovarian and endocrine responses in Nelore (Bos indicus) and Holstein (Bos taurus) heifers with differing feed intakes

Influence of GnRH analog and dose on LH release and ovulatory response in Bos indicus heifers and cows on day seven of the estrous cycle

This study evaluated the influence of GnRH analogs (gonadorelin vs. buserelin) and doses (single vs. double) on LH release and ovulatory response in Bos indicus (Nelore) females on Day 7 of the estrous cycle. Cycling heifers and non-lactating cows were pre-synchronized: Day -10: progesterone (P4) implant insertion plus 2 mg of estradiol benzoate; Day -2: implant removal and 0.53 mg of cloprostenol sodium (PGF); Day 0: 25 μg of lecirelin (GnRH). Over four replicates, heifers (n = 57) and cows (n = 53) that ovulated to the GnRH treatment on Day 0, having a visible corpus luteum (CL) and a dominant follicle (DF) ≥ 8.5 mm, were allocated to receive the following GnRH treatments on Day 7: G-Single (100 μg of gonadorelin); G-Double (200 μg of gonadorelin); B-Single (10 μg of buserelin); and B-Double (20 μg of buserelin). At GnRH treatment, a P4 implant was inserted in heifers (0.5 g) and cows (1 g). Ultrasound examinations were done on Days -10, -2, 0, 2, 7, 9, 12, and 14 to evaluate DF diameter, ovulation and presence of CL. Blood samples were collected on Day 7 at 0, 2, and 4 h from GnRH treatment, to evaluate circulating P4 and LH concentrations. On Day 12, the P4 implant was removed, females received two PGF treatments (24 h apart), and 2 d later, 25 μg of GnRH was given to start the next replicate. In both heifers and cows, P4 concentrations were elevated on Day 7, and similar among groups (3.9 and 4.2 ng/mL, respectively). In heifers, buserelin induced greater LH peak (9.5 vs. 2.6 ng/mL; P < 0.01) and greater ovulation (88.9 [24/27] vs. 16.7% [5/30]; P < 0.01) than gonadorelin treatments, regardless of the dose. Similarly, in cows, buserelin induced greater LH peak than gonadorelin (9.9 vs. 4.9 ng/mL; P < 0.01). However, ovulation was only increased in cows from the B-Double group (90.9% [10/11]), whereas in the other groups the ovulatory response was similar (35.7% [15/42]). Regardless of treatment, heifers had similar P4 concentrations (P = 0.22), but smaller DF (P < 0.01) than cows on Day 7. Only in G-Double group the LH peak was lower (P = 0.05) in heifers than in cows, with no difference within other groups. In heifers, but not in cows, the single dose of buserelin resulted in high ovulatory response, equivalent to that produced by the double dose. In conclusion, in Bos indicus heifers and cows on Day 7 of the cycle, with elevated P4 concentrations, buserelin induced greater LH release and ovulatory response than gonadorelin treatments. Double doses increased the LH release, however, only resulted in greater ovulation in females treated with buserelin. Finally, although circulating P4 concentrations did not differ between parities, heifers were more likely to ovulate in response to a GnRH-induced LH peak than cows.

Effects of long-acting injectable progesterone supplementation at early dioestrus on pregnancy maintenance in beef and dairy recipient cattle

We tested in the present study the hypothesis that supplementation with long-acting P4 (iP4) at different times of the initial dioestrus improves pregnancy rates in dairy and beef recipients submitted to fixed-time embryo transfer (FTET). Recipients from commercial farms had their oestrous cycle synchronized with an E2/P4-based protocol in three experiments (Exp. 1 to 3). In Exp. 1, dairy heifers (n = 76) and cows (n = 104) were randomly assigned to two experimental groups: the control group (n = 89) and the iP4D4 group (n = 91). For Exps. 2 and 3, suckled beef recipients were used. In Exp. 2, recipients were assigned to two experimental groups: Control group (n = 147) and iP4D7 group (n = 144); whereas in Exp. 3, recipients were randomly assigned to three experimental groups: Control group (n = 85), iP4-D4 group (n = 86) and iP4D7 group (n = 81). Recipients in the iP4D4 and iP4-D7 groups received an i.m. administration of 150 mg iP4, on D4 or D7 (D0 was the day of expected oestrus). On D7, all recipients were evaluated by transrectal ultrasonography and those that had a CL received a fresh or vitrified in vitro-produced embryo. In Exp. 2 and 3, the CL area was also determined by ultrasonography at the time of FTET. The pregnancy diagnosis was performed at 30 days in Exp. 1, 57 days in Exp. 2, and between 40 and 72 days of pregnancy in Exp. 3. In Exp. 1, the pregnancy rate did not differ (p > .1) between the Control group (38.2% [34/89]) and iP4D4 group (49.5% [45/91]); yet, a parity effect indicated a greater (p < .05) pregnancy rate in heifers (57.9% [44/76]) than cows (30.8% [32/104]). In Exp. 2, the pregnancy rate was greater (p < .05) in the iP4D7 group (45.0% [65/144]) than in the Control group (34.0% [50/147]). Also, a greater (p = .08) pregnancy rate was observed for recipients with a small CL (≤2.75 cm2 ) that were treated with iP4 on the day of FTET than the control recipients (46.4% [32/69] vs. 32.6% [28/86]). In Exp. 3, no significant effects (p > .1) of the treatment group or CL size were detected on pregnancy rates at days 30 and 60. In conclusion, the beneficial effects of iP4 supplementation at early dioestrus on pregnancy maintenance may vary according to the experimental conditions, but its use at the time of FTET can be used as an alternative to enhance the fertility of beef recipients in challenging conditions in commercial herds.

Review: Manipulation of follicle development to improve fertility of cattle in timed-artificial insemination programs

The development of an ovulatory follicle is a fundamental premise for any reproductive management program that aims to optimize fertility in cattle. Controlling follicular development comprises the synchronized emergence of a new follicular wave, selection and growth of the dominant follicle, and synchronized ovulation of a high-quality oocyte. All these follicular events, primarily driven by gonadotropin secretion, occur under a very dynamic hormonal environment. In this sense, controlling follicular development demands essentially a precise manipulation of the hormonal environment to modulate gonadotropin secretion. Furthermore, the effectiveness of hormonal manipulation strategies in the management of follicular development depends on specific particularities of each situation, which can vary widely according to genetic groups (Bos taurus vs Bos indicus), nutritional, metabolic, and reproductive status. In this regard, the constant search for the refined synchrony between the hormonal treatments and reproductive events, considering these distinctions and particularities, have provided valuable information that contributed to the development of efficient reproductive programs. This manuscript discusses the physiological bases behind the development of fine-tuned timed-artificial insemination protocols for beef and dairy cattle that resulted in great improvements in reproductive efficiency of beef and dairy herds.

High body energy reserve influences extracellular vesicles miRNA contents within the ovarian follicle

Aiming to evaluate the effects of increased body energy reserve (BER) in Nellore cows' reproductive efficiency, cows were fed with different nutritional plans to obtain animals with high BER (HBER; Ad libitum diet) and moderate BER (MBER: cows fed 70% of HBER group ingestion). To evaluate the BER, cows were weekly weighted and evaluated for subcutaneous fat thickness and insulin serum concentration along the experimental period. At the end of the experimental period, animals were submitted to estrous synchronization and artificial insemination. Animals were slaughtered approximately 120 h after ovulation induction and the reproductive tracts were collected for embryo recovery and samples collection. Cumulus-oocyte-complexes (COC) and follicular fluid were collected from 3-6 mm in diameter ovarian follicles to perform miRNA analysis of cumulus cells (CC) and extracellular vesicles from follicular fluid (EV FF). As expected, differences were observed among MBER and HBER groups for body weight, fat thickness, and insulin serum concentration. HBER animals showed lower ovulation and embryo recovery rates compared to MBER animals. Different miRNAs were found among CC and EV FF within groups, suggesting that the BER may influence follicular communication. This suggests that small follicles (3-6 mm diameter) are already under BER effects, which may be greater on later stages of follicular development.

What a 31-yr multibreed herd taught us about the influence of B. indicus genetics on reproductive performance of cows

Bos taurus × Bos indicus crosses are widespread in tropical and subtropical regions, nonetheless, quantitative information about the influence of B. indicus genetics on the reproductive performance of beef cattle is lacking. Herein, we determined the association between level of B. indicus genetics and reproduction from a 31-yr dataset comprising sequential breeding seasons of the University of Florida multibreed herd (n = 6,503 Angus × Brahman cows). The proportion of B. indicus genetics in this herd is evenly distributed by each 1/32nd or approximately 3-percentage points. From 1989 to 2020, the estrous cycle of cows was synchronized for artificial insemination (AI) based on detected estrus or timed-AI (TAI) using programs based on gonadotropin-releasing hormone and prostaglandin, and progestin/progesterone. All cows were exposed to natural service after AI and approximately 90-d breeding seasons, considering the day of AI as day 0. The proportion of B. indicus genetics of cows was associated negatively with pregnancy per AI, ranging from 51.6% for cows with 0%-19% of B. indicus genetics to 37.4% for cows with 81%-100% of B. indicus genetics. Similar association was found for estrous response at the end of the synchronization protocol, ranging from 66.3% to 38.4%, respectively. This reduced estrous response helped to explain the pregnancy results, once the pregnancy to AI of cows showing estrus was 2.3-fold greater than for those not showing estrus and submitted to TAI. Despite reduced pregnancy per AI, the increase in the proportion of B. indicus genetics of cows was not associated with a reduction in the proportion of pregnant cows at the end of the breeding season. Nevertheless, the interval from entering the breeding season to pregnancy was lengthened as the proportion of B. indicus genetics of cows increased. The median days to pregnancy was extended by 25 when the proportion of B. indicus genetics surpassed 78% compared with less than 20%. Thus, the increase in the proportion of B. indicus genetics of cows was related to a reduction in pregnancy per AI and lengthening the interval to attain pregnancy during the breeding season, but not with the final proportion of pregnant cows. As a result, reproductive management strategies directed specifically to cows with a greater proportion of B. indicus genetics are needed to improve the rate of pregnancy in beef herds.

Temporal evaluation of follicular dynamics and endocrine patterns of Holstein (Bos taurus), Gir (Bos indicus), and Murrah (Bubalus bubalis) heifers kept under the same nutritional, management and environmental conditions

The objective of the study was to simultaneously compare ovarian follicular dynamics and endocrine parameters of taurine (Holstein; n = 14), zebuine (Gir; n = 5), and bubaline (Murrah; n = 15) heifers kept under the same environmental, nutritional and management conditions. Heifers were synchronized with two PGF treatments 14 days apart. Ovaries of cyclic heifers were scanned daily during two consecutive ovulations and blood samples were collected every 24 h from each animal. No significant difference was found for length of interovulatory interval, however, zebuine heifers presented a greater number of follicular waves, number of antral follicles on day of ovulation, and higher insulin concentration than the other two breeds. Taurine heifers had highest maximal diameter of first wave dominant and ovulatory follicles and CL volume. Taurine and bubaline heifer's dominant follicle of first wave had longer static and regression phases than zebuine heifers. Bubaline heifers presented overall lowest progesterone concentrations and CL volume, but higher IGF1 levels. No difference was observed between taurine and zebuine heifers regarding IGF1 concentration. Despite higher CL volume found in taurine heifers, no difference in mean progesterone concentration was observed between them and zebuine heifers. Insulin and IGF1 concentrations were greater in follicular phase than in luteal phase when breed was not evaluated. After evaluating the three breeds simultaneously, at the same nutritional and management status it is possible to conclude that each genetic group has a specific follicular development and endocrinology of the estrous cycle.

Progesterone release profile and follicular development in Nelore cows receiving intravaginal progesterone devices

This study aimed to evaluate the progesterone (P4) release profile provided by four commercially available intravaginal P4 devices, as well as the effect of circulating P4 concentrations exclusively from these devices on the development of the dominant follicle (DF) in Nelore (Bos indicus) cows. Therefore, non-lactating multiparous Nelore cows were enrolled in an experimental design, over three replicates, starting on Day -9 with the insertion of a reused P4 device (2 g - original P4 load) for 7 d, followed by two treatments of cloprostenol sodium (PGF; 0.482 mg), 24 h apart, on Days -3 and -2. Just before device removal, on Day -2, a norgestomet ear implant was inserted and, 2 d later (Day 0), at the time of norgestomet withdrawal, cows were randomly assigned to receive one of the intravaginal devices: Primer (0.5 g); Prociclar (0.75 g); Sincrogest (1 g); or CIDR (1.9 g), and 2 mg of estradiol benzoate (EB) im. Blood samples were collected immediately before P4 device insertion, 12 h later and daily over 15 d (1 d after P4 device removal). Ultrasound examinations were performed on Days 0, 7, 8, 9, 10, 12, and 14 to evaluate ovarian dynamics. Results are presented as mean ± SEM and differences were considered when P ≤ 0.05. Overall, the devices resulted in distinct circulating P4 concentrations over 10 d, varying according to their initial P4 load and P4 impregnated surface area. Primer provided the lowest circulating P4 concentrations over time, whereas, CIDR had the greatest concentration. Sincrogest and Prociclar were similar, producing intermediary circulating P4. There was no effect of treatment on the DF diameter on any specific day, nor on follicular growth rate from Day 7-10. However, the Primer device resulted in a greater mean DF diameter over time. Additionally, greater circulating P4 concentrations, mainly during the first 3 d of device insertion, were associated with smaller DF diameters regardless of the treatment. In conclusion, results from this study provided a better understanding of the P4 profile of intravaginal P4 devices, as well as, their effect on DF development in Bos indicus cows. These data contribute to optimize the use of P4 devices in the reproductive management of beef cattle.

Progesterone release profile and follicular development in Holstein cows receiving intravaginal progesterone devices

The aim of this study was to evaluate the progesterone (P4) release profile provided by eight commercial intravaginal P4 devices, as well as the effect of circulating P4 concentrations produced exclusively by these devices on the development of the dominant follicle (DF) in non-lactating multiparous Holstein cows. All cows were submitted to the same experimental design starting with the insertion of a reused P4 device (2 g - original P4 load) for 7 d, followed by two treatments of cloprostenol sodium (PGF; 0.482 mg), 24 h apart, 6 and 7 d after device insertion. Just before device removal, a Norgestomet ear implant was inserted and, 2 d later (Day 0), simultaneously to Norgestomet withdrawal, cows received one of the tested intravaginal devices and 2 mg of estradiol benzoate (EB) im. In Exp.1 (n = 22; three replicates), cows were randomized to receive: CIDR (1.38 g); PRID-Delta (1.55 g); Prociclar (0.75 g); or Repro sync (2 g). In Exp. 2 (n = 29; four replicates), cows were randomized to receive: Cue-Mate (1.56 g); DIB 0.5 (0.5 g); DIB (1 g); PRID-Delta (1.55 g); or Sincrogest (1 g). Blood samples were collected before P4 device insertion (Day 0), 12 h later and daily over 15 d (1 d after P4 device removal). Ultrasound examinations were performed to evaluate growth of the DF on Days 0, 7, 8, 9, and 10. Results are presented as mean ± SEM and differences were considered when P ≤ 0.05. Overall, the circulating P4 profile and mean circulating P4 over 10 d differed among treatments. However, no effects were observed on the DF diameter and follicular growth rate from Day 7-10 after P4 device insertion. In Exp. 2, devices that provided higher circulating P4 concentrations were associated to a slower DF growth during the treatment period. Finally, this study provided a better understanding of the P4 release profile produced by intravaginal P4 devices as well as their effect on circulating P4 concentrations and DF development in non-lactating Holstein cows.

Early resynchronization of follicular wave emergence among Nelore cattle using injectable and intravaginal progesterone for three timed artificial inseminations

Follicular dynamics and pregnancy per AI (P/AI) of cattle submitted to resynchronization 13 d after TAI using a progesterone (P₄) insert and supplementary injectable progesterone (iP₄) were determined. There was synchronization of ovulation timing imposed (Day 0 = expected estrus; Experiment 1). On Day 13, animals were assigned to: control (only P₄ insert; 15 cows and 13 heifers) and iP4 (P₄ insert+100 mg iP₄; 13 cows and 12 heifers) groups, and submitted to daily ovarian ultrasonography and blood collection (Day 13 to Day 22). In Experiment 2, 760 suckled cows and 498 heifers were submitted to a TAI on Day 0 and assigned into control and iP4 groups on Day 13. In animals with luteolysis on Day 22, there was a second TAI on Day 24, and on Day 37 were subjected to the opposite treatments as imposed in first resynchronization procedure. On Day 37, there was pregnancy diagnosis in animals with functional CL. The third TAI was performed on Day 48. Day of follicular wave emergence did not differ between groups and parities. Dominant follicles were larger in cows than heifers, and in animals of the control group on Day 24. Greater P₄ concentrations were detected on Day 14 and Day 15 in the iP₄-treated animals. Luteolysis occurred earlier in cows than heifers. Overall P/AI percentage as a result of second and third TAIs, regardless of parity, was greater in iP₄-treated animals. In conclusion, females treated with a supplementary iP₄ had a greater plasma P₄ concentration and P/AI, but there was no effect of iP₄ treatment on synchrony of timing of follicular wave.

In vitro performance of Zebu (Bos indicus) and Taurus (Bos taurus) donor cow embryos

ABSTRACT In this study, the in vitro production of bovine embryos from zebu and taurine donors was compared. Cumulus-oocyte complexes (COCs) were obtained from 167 Bos taurus and 161 Bos indicus donors by ovum pick-up. COCs were classified based on their morphological quality, matured in incubators for 22 to 24 h in maturation medium, and then fertilized for 18 to 22 h. The zygotes were transferred to the culture medium for seven days. The embryos were classified as morula (OM), initial blastocyst (BI), blastocyst (BL), and expanded blastocyst (BX), before being transferred to synchronized recipient cows. Pregnancy was diagnosed 30-45 days post-transfer. The Bos indicus donors had a higher oocyte yield (n = 2556) than Bos taurus donors (n = 1903) (P = 0.008). The COCs from zebu donors had a better morphological quality than those from taurine donors (n = 689 vs. 444 for grade 1 COC, P < 0.0001; n = 681 vs. 509 for grade 2 COC, P = 0.010, for zebu and taurine donors, respectively). There were differences in embryo production percentages obtained from OM (0.44% from zebu and 6.42% from taurine, P = 0.017), BL (14.18% from zebu and 3.74% from taurine, P < 0.0001), and BX (81.43% from zebu and 75.13% from taurine, P < 0.0001). No significant difference was observed for embryo production from BI and pregnancy rate (P > 0.05). The Bos indicus cows showed greater oocyte recovery, number of viable oocytes, and production of viable embryos than the Bos taurus cows.