Increased dietary energy alters follicle dynamics and wave patterns in heifers

Optimizing ReBreed21 I: Evaluation of endocrine and ovarian dynamics in non-bred Bos indicus heifers

The present study evaluated follicular and endocrine dynamics during ReBreed21, a reproductive strategy that allows resynchronization of ovulation every 21 days in Bos indicus (Nelore) heifers. A synchronized estrous cycle was induced using a standard timed ovulation protocol (d -10: P4 implant inserted + 2 mg estradiol benzoate; d -2: P4 removed+ 0.5 mg cloprostenol + 0.6 mg estradiol cypionate + 200 IU equine chorionic gonadotropin (eCG); d0: 8.4 μg buserelin) without AI to ensure nonpregnancy in heifers. Day of GnRH was designated d0 of estrous cycle. On d12, heifers (n = 80) were randomized into three experimental groups: (1) ReBreed21 (n = 28) d12 P4 device inserted, d19 P4 device withdrawal plus 200 IU eCG, and d21 8.4 μg buserelin (GnRH); (2) ReBreed21+G (n = 26) same as ReBreed21 plus GnRH (16.8 μg) treatment on d12; and (3) Control (n = 26) no treatment. ReBreed21+G increased two-fold (62.9%; 18/26) percentage of heifers with synchronized follicular wave emergence compared to Control (34.6%; 9/26) whereas ReBreed21 (53.6%; 15/28) was intermediate. The ReBreeed21 groups (eCG on d19) increased (P < 0.01) follicular growth between d19 and d21 in ReBreed21 (2.3 ± 0.2 mm) and ReBreed21+G (3.4 ± 0.2 mm) compared with Control (1.2 ± 0.3 mm), resulting in greater (P < 0.01) follicle diameter on d21 for ReBreed21 (10.7 ± 0.4 mm) and ReBreed21+G (10.8 ± 0.4 mm) compared with Control (9.1 ± 0.5 mm). Structural luteolysis was similar among groups (P = 0.51), although the average day when P4 was <1 ng/mL was later (P < 0.01) for ReBreed21 (20.5 ± 0.2) and ReBreed21+G (20.7 ± 0.2) compared to Control (19.2 ± 0.4). Overall ovulation at the end of the estrous cycle was increased (P = 0.03) for ReBreed21 groups (83.3%; 45/54) compared with Control (57.7%; 15/26). Synchronized ovulation on day 22-23 was greater (P < 0.01) for ReBreed21 (78.6%; 22/28) and ReBreed21+G (76.9%; 20/26) compared with Control (30.8%; 8/26). Thus, the ReBreed21 resynchronization program produced acceptable endocrine and follicular dynamics, including synchronized ovulation at the end of the protocol in nonpregnant heifers providing good rationale for testing the fertility and practical implementation of this protocol under field conditions.

The ovarian function and endocrine phenotypes of lactating dairy cows during the estrous cycle were associated with genomic-enhanced predictions of fertility potential

The objectives of this prospective cohort study were to characterize associations among genomic merit for fertility with ovarian and endocrine function and the estrous behavior of dairy cows during an entire, non-hormonally manipulated estrous cycle. Lactating Holstein cows entering their first (n = 82) or second (n = 37) lactation had ear-notch tissue samples collected for genotyping using a commercial genomic test. Based on genomic predicted transmitting ability values for daughter pregnancy rate (gDPR) cows were classified into a high (Hi-Fert; gDPR > 0.6 n = 36), medium (Med-Fert; gDPR -1.3 to 0.6 n = 45), and low fertility (Lo-Fert; gDPR < -1.3 n = 38) group. At 33 to 39 DIM, cohorts of cows were enrolled in the Presynch-Ovsynch protocol for synchronization of ovulation and initiation of a new estrous cycle. Thereafter, the ovarian function and endocrine dynamics were monitored daily until the next ovulation by transrectal ultrasonography and concentrations of progesterone (P4), estradiol, and FSH. Estrous behavior was monitored with an ear-attached automated estrus detection system that recorded physical activity and rumination time. Overall, we observed an association between fertility group and the ovarian and hormonal phenotype of dairy cows during the estrous cycle. Cows in the Hi-Fert group had greater circulating concentrations of P4 than cows in the Lo-Fert group from d 4 to 13 after induction of ovulation and from day -3 to -1 before the onset of luteolysis. The frequency of atypical estrous cycles was 3-fold greater for cows in the Lo-Fert than the Hi-Fert group. We also observed other modest associations between genomic merit for fertility with the follicular dynamics and estrous behavior. There were several associations between milk yield and parity with ovarian, endocrine, and estrous behavior phenotypes as cows with greater milk yield and in the second lactation were more likely to have unfavorable phenotypes. These results demonstrate that differences in reproductive performance between cows of different genomic merit for fertility classified based on gDPR may be partially associated with circulating concentrations of P4, the incidence of atypical phenotypes during the estrous cycles, and to a lesser extent the follicular wave dynamics. The observed physiological and endocrine phenotypes might help explain part of the differences in reproductive performance between cows of superior and inferior genomic merit for fertility.

Profiles of interferon-stimulated genes in multiple tissues and circulating pregnancy-associated glycoproteins and their association with pregnancy loss in dairy cows†

Pregnancy loss (PL) in lactating dairy cows disrupts reproductive and productive efficiency. We evaluated the expression of interferon-stimulated genes (ISG) in blood leukocytes, vaginal and cervical epithelial cells, luteolysis-related genes, progesterone, and pregnancy-associated glycoprotein (PAG) profiles in lactating dairy cows (n = 86) to gain insight about PL. Expression of ISG on d17, d19, and d21 was greater in cows that maintained the pregnancy (P33) compared to nonpregnant with no PL (NP). Greater ISG differences between groups were observed in the cervix (96.7-fold) than vagina (31.0-fold), and least in blood leukocytes (5.6-fold). Based on individual profiles of ISG and PAG, PL was determined to occur either before (~13%) or after (~25%) d22. For cows with PL before d22, ISG expression was similar on d17 but by d21 was lower and OXTR was greater than P33 cows and similar to NP; timing of luteolysis was similar compared to NP cows suggesting embryonic failure to promote luteal maintenance and to attach to the endometrium (no increase in PAG). For cows with PL after d22, ISG expression was similar to P33 cows on d17, d19, and d21 and luteolysis, when it occurred, was later than NP cows; delayed increase in PAG suggested later or inadequate embryonic attachment. In conclusion, PL before d22 occurred due to embryonic demise/failure to signal for luteal maintenance, as reflected in reduced ISG expression by d21. Alternatively, embryos with PL between d22 and 33 adequately signaled for luteal maintenance (ISG) but had delayed/inadequate embryonic attachment and/or inappropriate luteolysis causing PL.

Temporality of ovarian steroids and LH/FSH pulse profiles encompassing selection of the dominant follicle in heifers†

The tested hypotheses were (1) LH/FSH pulses and F2 diameter are diminished by P4 and, (2) E2 increases during the transition to deviation and alters LH/FSH pulses. On Day 5 (Day 0 = ovulation), heifers were randomized into an untreated group (HiP4, n = 11), and a prostaglandin analog treated group (NoP4, n = 10). On Day 6, a follicular wave was induced by follicle ablation. Ultrasound and blood collections were performed every 12 h from Days 7 to 11. Blood was collected every 15 min for 10 h on Day 9 (largest follicle expected to be ~7.5 mm). Estradiol was ~75% greater (0.36 ± 0.14 vs 0.63 ± 0.19 pg/mL) in heifers with F1 ≥ 7.2 mm than in heifers with F1 < 7.2 mm. The HiP4 had smaller second largest follicle (F2) diameter, lower estradiol (P = 0.06), LH pulse baseline and peak concentrations (P < 0.007), in addition to half the frequency of LH/FSH pulses (4.1 ± 0.3 vs 9.6 ± 0.7 in 10 h) than the NoP4. Within HiP4, heifers with F1 ≥ 7.2 mm had ~25% fewer (P = 0.03) LH pulses compared to heifers with F1 < 7.2 mm. In contrast, within the NoP4, heifers with F1 ≥ 7.2 mm had ~75% greater LH (P = 0.05) and FSH (P = 0.08) pulse amplitude. We propose that greater F2 diameter at deviation in low P4 is related to greater LH baseline and peak concentrations, and greater frequency of LH/FSH pulses. A greater increase in E2 after F1 reaches ~7.2 mm results in further stimulation of LH/FSH pulse amplitude. Elevated P4 not only diminished frequency of LH/FSH pulses but also converted an E2 increase into a negative feedback effect on LH/FSH pulse frequency leading to smaller F2 at deviation.

Is pregnancy loss initiated by embryonic death or luteal regression? Profiles of pregnancy-associated glycoproteins during elevated progesterone and pregnancy loss

Because progesterone (P4) is essential for pregnancy establishment and maintenance, we investigated the effect of increased concentrations of P4 on embryonic attachment and concentrations of pregnancy-associated glycoproteins (PAG). Additionally, we investigated the relationships among luteal regression, pregnancy loss, and PAG concentrations in cows undergoing pregnancy loss by d 33 of pregnancy. Lactating dairy cows were allocated into control (n = 40) and human chorionic gonadotropin (hCG; 3,300 IU on d 7 and 13 to promote greater circulating P4; GnRH = d 0; n = 46) groups. Progesterone was measured daily from d 7 to 33, and PAG was measured daily from d 17 to 33; both hormones were also measured on d 47 and 61. An increase in PAG >10% compared with d 17 was considered a marker for pregnancy. The gold standard for pregnancy diagnosis was ultrasound evaluation of embryonic heartbeat on d 33. Statistical analyses were done with PROC MIXED from SAS Institute Inc. Concentrations of P4 were greater from d 8 onward in the hCG group. Concentrations of PAG did not differ between groups from d 17 to 33, suggesting no effect of increased P4 on hastening embryonic attachment and placental development. Nevertheless, PAG was greater in the hCG group on d 47 and 61, suggesting greater placental area or PAG secretory capacity. Pregnancy loss between d 20 and 33 occurred in 24.6% of cows. About 50% of pregnancy loss was due to luteal regression and about 50% was due to conceptus failure; that is, a decrease in PAG in the absence of luteal regression. In conclusion, increased P4 does not hasten embryonic attachment or early placental development but it leads to increased PAG in the second half of the second month of gestation. Additionally, pregnancy loss seems to be initiated by either corpus luteum regression or conceptus failure.

History, insights, and future perspectives on studies into luteal function in cattle

The corpus luteum (CL) forms following ovulation from the remnant of the Graafian follicle. This transient tissue produces critical hormones to maintain pregnancy, including the steroid progesterone. In cattle and other ruminants, the presence of an embryo determines if the lifespan of the CL will be prolonged to ensure successful implantation and gestation, or if the tissue will undergo destruction in the process known as luteolysis. Infertility and subfertility in dairy and beef cattle results in substantial economic loss to producers each year. In addition, this has the potential to exacerbate climate change because more animals are needed to produce high-quality protein to feed the growing world population. Successful pregnancies require coordinated regulation of uterine and ovarian function by the developing embryo. These processes are often collectively termed "maternal recognition of pregnancy." Research into the formation, function, and destruction of the bovine CL by the Northeast Multistate Project, one of the oldest continuously funded Hatch projects by the USDA, has produced a large body of evidence increasing our knowledge of the contribution of ovarian processes to fertility in ruminants. This review presents some of the seminal research into the regulation of the ruminant CL, as well as identifying mechanisms that remain to be completely validated in the bovine CL. This review also contains a broad discussion of the roles of prostaglandins, immune cells, as well as mechanisms contributing to steroidogenesis in the ruminant CL. A triadic model of luteolysis is discussed wherein the interactions among immune cells, endothelial cells, and luteal cells dictate the ability of the ruminant CL to respond to a luteolytic stimulus, along with other novel hypotheses for future research.

Endometrial and luteal responses to a prostaglandin F2alpha pulse: A comparison between heifers and mares

In heifers and mares, multiple pulses of prostaglandin F2alpha (PGF) are generally associated with complete luteal regression. Although PGF pulses occur before and during luteolysis, little is known about the role of minor PGF pulses during preluteolysis on subsequent luteal and endometrial PGF production that may initiate luteolysis. Heifers (n = 7/group) and mares (n = 6/group) were treated with a single minor dose of PGF (3.0 and 0.5 mg, respectively) during mid-luteal phase (12 and 10 days postovulation in heifers and mares, respectively). After treatment, a transient decrease in progesterone (P4) concentrations occurred in heifers between Hours 0–2 but at Hour 4 P4 was not different from pre-treatment. In mares, P4 was unaltered between Hours 0 and 4. Concentrations of P4 decreased in both species by Hour 24 and complete luteolysis occurred in mares by Hour 48. Luteal and endometrial gene expression were evaluated 4 hours post-treatment. In heifers, luteal mRNA abundance of PGF receptor and PGF dehydrogenase were decreased while PTGS2, PGF transporter, and oxytocin receptor were increased. In the heifer endometrium, receptors for oxytocin, P4, and estradiol were upregulated. In mares, luteal expression of PGF receptor was decreased while PGF transporter and oxytocin receptor were increased. The decrease in P4 between Hours 4 and 24 and changes in gene expression were consistent with upregulation of endogenous synthesis of PGF. The hypotheses were supported that a single minor PGF treatment upregulates endogenous machinery for PGF synthesis in heifers and mares stimulating endogenous PGF synthesis through distinct regulatory mechanisms in heifers and mares.

Switching of follicle destiny so that the second largest follicle becomes dominant in monovulatory species

During an ovulatory follicular wave in the monovulatory species of heifers, mares, and women, the two largest follicles deviate in diameter at the end of a common follicle growth phase. The largest follicle before deviation becomes the future ovulatory follicle in most ovulatory waves. In 10-30% of the ovulatory waves, the destiny of the two follicles switches just before or at deviation so that the second-largest follicle becomes the future ovulatory follicle, and the largest follicle becomes a subordinate. In FSH-driven switching in heifers, mares, and women, the wave-stimulating FSH surge decreases to a low concentration before the largest follicle has developed the ability to utilize the low concentrations. The concentrations of FSH then increase (mares, women) or cease to decrease (heifers), and the next largest follicle acquires the capability of becoming the future ovulatory follicle. Luteolysis-driven switching has been reported in heifers but not in mares and women. The switching in heifers occurs during ovulatory wave 3 of three wave interovulatory intervals (IOI) when the wave of follicles is in the common growth phase in synchrony with the time of luteolysis. Regression of the CL during the common growth phase of ovulatory wave 3 is accompanied by decreased activity of follicles that are adjacent to the regressing CL but not when follicles and CL are separated or in opposite ovaries. The role of luteolysis in switching in heifers has been tested by treating with PGF2α when the largest follicle of wave 2 was near the end of the common growth phase. Switching in destiny of the largest follicle from the expected future dominant to a future subordinate occurred in most waves (10 of 17) when the largest follicle and regressing CL were in the same ovary and adjacent but not when separated in the same ovary or when in opposite ovaries (0 of 11). The newly selected future ovulatory follicle may develop in the opposite ovary. Thereby, frequency of the contralateral vs ipsilateral relationship between the preovulatory follicle and CL in heifers is greater in three-wave IOI than in two-wave IOI. In summary, the second largest predeviation follicle becomes the postdeviation dominant follicle when the decreasing FSH is out of phase with the largest predeviation follicle in heifers, mares, and women or when luteolysis and predeviation are in synchrony in heifers.

Side of ovulation at each end of two- and three-wave interovulatory intervals and before and after pregnancy in cattle

The side of ovulation (left ovary, LO; right ovary, RO) and side of the next ovulation were compared between (1) beginning and end of an interovulatory interval (IOI) and beginning and end of consecutive sets of two and three IOI (n = 900 IOI), (2) beginning and end of the IOI for two and three follicular waves per IOI (n = 1300), and (3) beginning of pregnancy and first postpartum ovulation (n = 793). Pairs of sides of ovulation were designated LL (LO and LO), RR, LR, and RL. The frequency of ovulation pairs for two ends of an IOI was not different from two ends of two or three consecutive IOI indicating that differences between LO and RO were more likely inherent than from factors that developed in each IOI. For each end of an IOI or two consecutive IOI, the least frequency (P < 0.05) was for LL (16 %) with no differences among RR, LR, and RL (28 % for each). Frequencies between ipsilateral (LL, RR) and contralateral (LR, RL) ovulations pairs were not different for two-wave IOI (48 % compared with 52 %) but differed (P < 0.0001) for three-wave IOI (32 % compared with 68 %) and for pregnancy/postpartum (34 % compared with 66 %). In pregnancy/postpartum, each pair was different (P < 0.05) from each other: LL (13 %), RR (21 %), LR (30 %), RL (36 %). The lesser frequency for LL than for any of the others for an IOI, consecutive IOI, and pregnancy/postpartum indicated a ubiquity of the small propensity for LO ovulation.