Delayed effect of progesterone on endometrial morphology in dairy cows

Phenotypic and Genetic Analyses of In Vitro Embryo Production Traits in Chinese Holstein Cattle

Ovum pick up and in vitro embryo production (OPU-IVEP) is an essential technique in the dairy industry. The production efficiency of OPU-IVEP is significantly influenced by various factors, and phenotypic and genetic characteristics are highly variable in different populations. The objectives of this study were (1) to reveal the phenotypic characteristics, including population distribution, and impacts of donor age and month on in vitro embryo production and (2) to estimate genetic parameters for five in vitro embryo production traits in Chinese Holstein cattle. A total of 7311 OPU-IVEP records of 867 Holstein heifers from August 2021 to March 2023 were collected in this study. Five in vitro embryo production traits were defined, including the number of cumulus-oocyte complexes (NCOC), the number of cleaved embryos (NCLV), the number of grade I embryos (NGE), and the proportion of NCLV to NCOC (PCLV) and NGE to NCOC (PGE). A univariate repeatability animal model was employed to estimate heritability and repeatability, and a bivariate repeatability animal model was employed to estimate the genetic correlations among five in vitro embryo production traits. It was found that the in vitro embryo production traits were significantly influenced by season, as the NGE and PGE were significantly decreased from June to August. In addition, the production efficiency of OPU-IVEP was also influenced by donor age. On the observed scale, the estimates of heritability were 0.33 for NCOC, 0.24 for NCLV, 0.16 for NGE, 0.06 for PCLV, and 0.10 for PGE, respectively. On the log-transformed scale, the estimates of heritability of NCOC, NCLV, and NGE were 0.34, 0.18, and 0.13. The genetic correlations among NCOC, NCLV, and NGE ranged from 0.61 (NCLV and NGE) to 0.95 (NCOC and NCLV), considering both scales. However, there were low genetic correlations between NCOC and proportion traits (PCLV and PGE) on both the observed scale and the log-transformed scale. In the end, the variation in Chinese Holstein cattle was found to be considerable. The EBV value and average NCOC, NGE, and PGE for the top 10% donors presented extreme differences to those for the bottom 10% donors for NCOC (24.02 versus 2.60), NGE (3.42 versus 0.36), and PGE (30.54% versus 3.46%). Overall, the results of this study reveal that in vitro embryo production traits are heritable with low to high heritability, and the count traits (NCOC, NCLV, and NGE) and proportion traits (PCLV and PGE) reflect different aspects of in vitro embryo production and should be incorporated into genetic selection for improving the embryo production efficiency of dairy cattle.

Effect of a progesterone-releasing intravaginal device (PRID) for 8 days during a modified Ovsynch protocol on pregnancy outcomes in lactating Holstein cows

Our objective was to evaluate the effect of a progesterone-releasing intravaginal device (PRID) in a 7-d Ovsynch protocol on pregnancy per artificial insemination (P/AI) and pregnancy loss, compared with a standard 7-d Ovsynch protocol without progesterone supplementation. We hypothesized that progesterone supplementation during an Ovsynch protocol would increase P/AI and decrease pregnancy loss. Data were collected on lactating Holstein cows (n = 716) that either received a 7-d Ovsynch protocol (control: d 0, 100 µg of GnRH; d 7, 500 µg of cloprostenol; d 9, µg of GnRH; n = 360) or a modified Ovsynch protocol with addition of a PRID (PRIDsynch; d 0, 100 µg of GnRH + PRID; d 7, 25 mg of dinoprost; d 8, PRID removal; d 9, 100 µg of GnRH; n = 356). All cows received timed artificial insemination (TAI) approximately 16 h after the second GnRH treatment. Pregnancy diagnosis was performed via ultrasonography on d 38 ± 3 after TAI and rechecked on d 80 ± 7 after TAI. Reproductive performance differed between treatments, with PRIDsynch cows having greater (38.9%) P/AI compared with control cows (31.7%) at d 38 ± 3 and also at d 80 ± 7 (34.6% vs. 28.9%, for PRIDsynch and control cows, respectively). Pregnancy loss did not differ among treatments.

Effects of progesterone concentrations and follicular wave during growth of the ovulatory follicle on conceptus and endometrial transcriptome in dairy cows

Objectives were to evaluate the effects of follicular wave and progesterone concentration on growth of the ovulatory follicle, conceptus elongation, uterine IFN-τ concentration, and transcriptome of conceptus and endometrium of pregnant cows on d 17 of gestation. Nonlactating nonpregnant Holstein cows were assigned randomly to one of 3 treatments: ovulation of a first-wave follicle (FW, n = 15); ovulation of a first-wave follicle and progesterone supplementation (FWP4, n = 12); and ovulation of a second-wave follicle (SW, n = 19). Ovulation of a first- or second-wave follicle was achieved by initiating the Ovsynch protocol (d -9 GnRH, d -2 and -1 PGF_2α, d 0 GnRH and artificial insemination, d 0.7 artificial insemination) on d 0 or 6 of a presynchronized estrous cycle, respectively. Cows in FWP4 received 3 intravaginal inserts containing progesterone at 12, 24, and 48 h after the first GnRH injection that were removed on d -2. Cows were killed on d 17 for collection of the reproductive tract. Transcriptome was evaluated by microarray using the Affymetrix Bovine Array. Orthogonal contrasts were built to assess the effects of progesterone concentration during follicle growth (FW vs. FWP4 + SW) and follicular wave (FWP4 vs. SW). Progesterone concentrations (LSM ± SEM) from d -9 to -2 were greater for SW, followed by FWP4 and FW (5.38 ± 0.24, 4.26 ± 0.28, and 1.17 ± 0.27 ng/mL). Diameter of the ovulatory follicle (FW = 19.6 ± 0.6; FWP4 = 15.6 ± 0.6; SW = 15.2 ± 0.5 mm) and concentrations of estradiol from d -2 to 1 (FW = 4.05 ± 0.33; FWP4 = 2.73 ± 0.35; SW = 2.48 ± 0.30 pg/mL) were greater for FW compared with FWP4 and SW. Progesterone concentrations from d 3 to 16 were greater for FW compared with FWP4 and SW. A total of 28 singleton conceptuses were collected (FW, n = 8; FWP4, n = 8; SW, n = 12) and only intact conceptuses were included in the analyses of length (FW, n = 8; FWP4, n = 6; SW, n = 12). Although conceptuses were longer for FW compared with FWP4 and SW (FW = 16.6 ± 2.3; FWP4 = 9.8 ± 2.2; SW = 9.6 ± 2.0 cm), treatment did not affect the amount of IFN-τ in uterine flushing. Transcriptome of conceptuses and endometrium of pregnant cows was not extensively affected by follicular wave (8 and 1 differentially expressed transcripts) or concentration of progesterone during follicle growth (0 and 3 differentially expressed transcripts), showing that these factors did not affect conceptuses and endometrium transcriptome in pregnancies that are maintained to d 17.

Characterization of the endometrial transcriptome in early diestrus influencing pregnancy status in dairy cattle after transfer of in vitro-produced embryos

Modifications of the endometrial transcriptome at day 7 of the estrus cycle are crucial to maintain gestation after transfer of in vitro-produced (IVP) embryos, although these changes are still largely unknown. The aim of this study was to identify genes, and their related biological mechanisms, important for pregnancy establishment based on the endometrial transcriptome of recipient lactating dairy cows that become pregnant in the subsequent estrus cycle, upon transfer of IVP embryos. Endometrial biopsies were taken from Holstein Friesian cows on day 6-8 of the estrus cycle followed by embryo transfer in the following cycle. Animals were classified retrospectively as pregnant (PR, n = 8) or nonpregnant (non-PR, n = 11) cows, according to pregnancy status at 26-47 days. Extracted mRNAs from endometrial samples were sequenced with an Illumina platform to determine differentially expressed genes (DEG) between the endometrial transcriptome from PR and non-PR cows. There were 111 DEG (false discovery rate < 0.05), which were mainly related to extracellular matrix interaction, histotroph metabolic composition, prostaglandin synthesis, transforming growth factor-β signaling as well as inflammation and leukocyte activation. Comparison of these DEG with DEG identified in two public external data sets confirmed the more fertile endometrial molecular profile of PR cows. In conclusion, this study provides insights into the key early endometrial mechanisms for pregnancy establishment, after IVP embryo transfer in dairy cows.

Absence of a corpus luteum and relatively lesser concentrations of progesterone during the period of pre-ovulatory follicle emergence results in lesser pregnancy rates in Bos indicus cattle

Concentrations of progesterone before AI have had variable effects on fertility in both Bos indicus and Bos taurus cattle. The aim of this study was to determine if fertility and concentrations of progesterone after AI were affected in Bos indicus females when pre-ovulatory follicles develop in the absence or presence of a corpus luteum (CL). Between 6.5-7.5 days after a synchronised oestrus, all follicles ≥4 mm in diameter were aspirated (Day 0) and cloprostenol was administered on Days 0 and 1 (LP4, n = 36) or on Days 4 and 5 (HP4, n = 40). Animals were inseminated on detection of oestrus until Day 9. Breeding continued using natural mating between Days 9 and 19, AI on detection of oestrus between Day 19 and 29 and natural mating between Days 29-90. Mean concentrations of progesterone were less on Days 2-4 in the LP4 compared to the HP4-treated animals but similar on Days 14 and 20. In the LP4- compared to the HP4-treated animals, the odds of being detected in oestrus and ovulating close to the first AI were similar, but odds of pregnancy to first AI (OR = 0.19, 95% CI 0.07 - 0.52) and after 1, 4 and 13 weeks of breeding were less (P ≤  0.051). Absence of a CL and relatively lesser concentrations of progesterone during emergence of pre-ovulatory follicles resulted in lesser pregnancy rates to AI in Bos indicus cattle but did not affect concentrations of P4 after ovulation.

Effect of plasma progesterone on oocyte recovery, oocyte quality, and early in-vitro developmental competence of embryos in Bos indicus dairy cows

The objective of present study was to determine the effect of plasma progesterone (P4) on oocyte recovery, oocyte quality, and early in-vitro developmental competence of embryos in Bos indicus dairy cows. The ovaries were collected in an abattoir. These ovaries (n = 750) were divided into two groups: 1) estrous CYCLIC (n = 318), and 2) estrous ACYCLIC (n = 432). Mean serum concentrations of P4 in a subset of (n = 85; 4.21 ± 0.4 ng/ml compared with 0.5 ± 0.2 ng/ml; P <  0.05) were greater in estrous CYCLIC as compared to ACYCLIC cows, respectively. The mean number of oocytes recovered per ovary (6.5 ± 0.5 compared with 4.0 ± 0.2; P <  0.05) was greater for estrous CYCLIC than ACYCLIC cows, respectively. The oocytes with grade I_+_II quality (55.3% compared with 47.6%; P <  0.05) were greater, whereas, there was lesser percentage with grade III_+_IV quality (44.5% compared with 52.4%; P <  0.05) from estrous CYCLIC as compared with ACYCLIC cows, respectively. Cleavage rate (70.9% compared with 52.8%; P < 0.05) was greater for embryos derived from estrous CYCLIC than ACYCLIC cows, respectively. Similarly, the embryo developmental rates to the 8- (38.5% compared with 20.8%; P < 0.05) and 16- (20.0% compared with 10.9%; P < 0.05) cell stage were greater for embryos derived from estrous CYCLIC as compared to ACYCLIC cows, respectively. In conclusion, the presence of greater plasma P4 has a beneficial effect on oocyte recovery, oocyte quality, and early IVEP outcomes in Bos indicus dairy cows.

Nutritional effects on resumption of ovarian cyclicity and conception rate in postpartum dairy cows

Increased genetic potential for milk production has been associated with a decline in fertility of lactating cows. Following parturition the nutritional requirements increase rapidly with milk production and result in negative energy balance (NEBAL). NEBAL delays the time of first ovulation thereby affecting ovarian cycles before and during the subsequent breeding period The effects of NEBAL on reinitiation of ovulation are manifested through inhibition of LH pulse frequency and low levels of glucose, insulin and IGF-I in blood that collectively restrain oestrogen production by dominant follicles. Upregulation of LH pulses and peripheral IGF-I in association with the NEBAL nadir increases the likelihood that emerging dominant follicles will ovulate. The legacy of NEBAL is reduced fertility after insemination in conjunction with reduced serum progesterone concentrations. Diets high in crude protein support high milk yield, but may be detrimental to reproductive performance. Depending upon protein quantity and composition, serum concentrations of progesterone may be lower and the uterine luminal environment is altered. High protein intake is correlated with plasma urea concentrations that are inversely related to uterine pH and fertility. The direct effects of high dietary protein and plasma urea on embryo quality and development in cattle are inconsistent. In conclusion, the poor fertility of high producing dairy cows reflects the combined effects of a uterine environment that is dependent on progesterone, but has been rendered suboptimal for embryo development by antecedent effects of negative energy balance and may be further compromised by the effects of urea resultingfrom intake of high dietary protein.

Targeted progesterone supplementation improves fertility in lactating dairy cows without a corpus luteum at the initiation of the timed artificial insemination protocol

The objectives of this study were to determine the effect of supplemental progesterone on fertility in lactating dairy cows lacking a corpus luteum (CL) at the initiation of the timed artificial insemination (AI) program. Holstein cows were subjected to the 5-d timed AI program (d -8 GnRH, d -3 and -2 PGF2α, d 0 GnRH and AI). Cows had their ovaries scanned by ultrasonography on d -8 and those bearing a CL were considered to be in diestrus (DI; n=946). Cows that lacked a CL on d -8 were assigned to remain as untreated control (CON; n=234) or receive 2 controlled internal drug release (CIDR) inserts containing progesterone (2CIDR; n=218) from d -8 to -3, as a single insert has been proven insufficient to modulate fertility in cows without CL. Blood was analyzed for progesterone and estradiol concentrations. Pregnancy was diagnosed on d 34 and 62 after AI. Progesterone concentrations during the timed AI program were lowest for CON, intermediate for 2CIDR, and highest for DI. Supplementation increased progesterone concentrations between d -7 and -3 compared with CON (2.65 vs. 0.51 ng/mL). Ovulation to the first GnRH was not affected by treatment. However, a greater proportion of CON and 2CIDR cows had a new CL on d -3 compared with DI cows (66.7 vs. 61.9 vs. 52.0%). In cows with a new CL, the diameter of the ovulatory follicle was larger for CON than 2CIDR, and intermediate for DI (18.7 vs. 16.5 vs. 17.7 mm). Concentrations of estradiol on d -3 did not differ among treatments; however, DI cows had greater estradiol concentrations at AI compared with CON or 2CIDR cows. Pregnancy per AI was less for CON compared with 2CIDR or DI on d 32 (30.8 vs. 46.8 vs. 49.9%) and 64 (28.6 vs. 43.7 vs. 47.3%), indicating that supplementation with progesterone reestablished fertility in cows lacking a CL on d -8. A greater proportion of nonpregnant CON cows had a short reinsemination interval compared with 2CIDR or DI (11.1 vs. 3.5 vs. 5.7%). Treatment did not affect pregnancy loss between d 34 and 62 of gestation. A single ultrasound exam was effective in identifying a low-fertility cohort of cows based on the absence of CL at the first GnRH injection of the timed AI protocol. Progesterone supplementation with 2 CIDR inserts increased progesterone in plasma to 2.65 ng/mL and restored fertility in lactating dairy cows lacking a CL at the initiation of the timed AI program similar to that of cows in diestrus.

The use of endocrine treatments to improve pregnancy rates in cattle

Reproduction is critical for the success of both dairy and beef cattle production. Inadequate reproduction impairs profitability by compromising production, delaying genetic progress and increasing expenses. A major impediment to the use of artificial insemination (AI) is the ability to detect oestrus for optimum timing of breeding. However, increased understanding of the bovine oestrous cycle has led to the development of reproductive programmes that allow precise synchrony of follicle development, luteal regression and ovulation. The advent of timed-AI protocols revolutionised reproductive management in dairy and beef herds. It allows for AI at a more desired time post partum despite oestrous cyclicity. It also allows for pre-determined re-insemination of cows diagnosed as not pregnant. In subfertile cows, such as the post partum, anoestrous beef cow and the high-producing dairy cow, strategic hormone supplementation has been used to overcome hormone deficiencies and improve pregnancy rates. Several physiological windows have been identified to optimise fertility in synchronisation programmes and they include, but are not limited to, follicle turnover, synchrony of follicular development, length of dominance, progesterone concentrations during development of the ovulatory follicle, luteal regression, peri-ovulatory steroid concentrations, length of pro-oestrus, synchrony of ovulation and AI, and progesterone rise after ovulation.

Impact of estrous synchronization methods on cellular proportions in cervical mucus and serum hormone concentrations

The objective of this study was to examine cytological changes of cervical mucus following the induction of estrus with intra-vaginal drug release (CIDR) devices in dairy cows. Sixty healthy Holstein Frisian cows, averaging 80 (+/-10) days post-partum, were selected from a commercial dairy farm around Shiraz. Cows in the control group were synchronized by the Ovsynch protocol. Cows in the second group (OV+CIDR) were subjected to the same Ovsynch protocol but in addition were administered a progesterone-releasing CIDR. Cows in the third group (OV+S-CIDR) were subjected to Ovsynch procedures but received the skeleton of a CIDR device, which did not release progesterone. Cows in the fourth group (E2+CIDR) received a progesterone releasing CIDR but were injected with estradiol benzoate. Cows in group 5 (E2+S-CIDR) received a CIDR skeleton and estrodial benzoate. CIDR devices were removed from cows in groups 2-4 and all cows were injected with PGF2alpha on day -3. Blood samples and cervical mucus discharges were collected from all cows on days -10, -3, 0 and 12 relative to AI. On the day of AI, the mean+/-S.D. percentage of neutrophils was significantly higher (p<0.05) in the S-CIDR+OV and S-CIDR+E2 groups than in Ovsynch group. Comparing the percentage of neutrophils in cervical mucus of Ovsynch group (less than 1%) with that of other treatment groups on the day of AI (from 5 to 39%) revealed the influential effect of a CIDR device on the reproductive tract. Results of the current study did not reveal hormonal effects but did identify mechanical effects of CIDRs on cell percentages in cervical mucus. The hormonal effects were probably masked by mechanical effects. Therefore, we were not able to confirm hormonal effects on proportions of different cells in cervical mucus. Consequently, additional research on hormonal effects and the mechanical effects of CIDR on the uterus is required.

Preovulatory, postovulatory, and postmaternal recognition effects of concentrations of progesterone on embryonic survival in the cow

Although fertilization rate usually is very high when male fertility is normal, pregnancy rates are below expectations when defined by the birth of live offspring in response to first service. Factors that affect establishment and retention of pregnancy include 1) preovulatory influences on the follicle and oocyte, 2) early postovulatory uterine and luteal function, 3) concentrations of hormones associated with trophoblastic and endometrial function during maternal recognition of pregnancy, and 4) less-well understood factors during the peri-attachment period. For example, decreased progesterone during preovulatory follicular development leads to a persistent follicle, premature resumption of meiosis, and a high incidence of embryonic death between the 2- and 16-cell stages. Elevated PGF(2alpha) during d 4 to 9 of the estrous cycle not only caused luteolysis but also had a direct embryotoxic effect during the morula-to-blastocyst transition. Ideal conditions during placentation and attachment are not clearly defined. Late embryonic mortality might be increased after ovulation of persistent or immature follicles. Nominal increases in secretion of PGF(2alpha) between d 30 and 35 might be important for attachment and placentation. Lower survival of embryos from wk 5 to wk 7 to 9 of gestation in the cow was associated with lower circulating concentrations of progesterone on wk 5. To maximize embryonic survival in the cow, management must provide high progesterone before estrus, quality detection of estrus, and timely insemination. Luteolytic influences of estradiol-17beta or PGF(2alpha) must be minimized early after mating and during maternal recognition of pregnancy, and high progesterone is needed during the late embryonic/early fetal period.

Relations between Plasma IGF-I Concentrations during Treatment with CIDR-based or Ovsynch Protocol for Timed AI and Conception in Early Postpartum Japanese Black Beef Cows

We examined the relations between plasma insulin-like growth factor (IGF) -I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception and plasma steroid concentrations in early postpartum Japanese Black beef cows. Cows in the control group (Ovsynch; n = 21) underwent Ovsynch protocol (GnRH analogue on Day 0, PGF(2alpha) analogue on Day 7, and GnRH analogue on Day 9), with AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the Ovsynch+CIDR group (n = 22) received Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Cows in the further treatment group (EB+CIDR+GnRH; n = 22) received 2 mg of estradiol benzoate (EB) on Day 0 in lieu of the first GnRH treatment, followed by the same treatment as in the Ovsynch+CIDR protocol. Plasma IGF-I concentrations were determined on Days -7, 0, 7, 9 and 17. Conception rates were improved in the CIDR-combined groups (both CIDR-treated groups were combined) relative to Ovsynch group (P < 0.05) for cows with low IGF-I concentrations (<1,000 ng/ml) on Days -7, 0, and 7, but improved conception rate produced by the CIDR-based protocols did not occur in cows with a high IGF-I concentration (> or =1,000 ng/ml). Plasma estradiol-17beta concentrations increased from Day 0 to 7 (P < 0.05) and were unchanged from Day 7 to 9 in the Ovsynch group with low IGF-I concentrations on Day 0, while they were unchanged from Day 0 to 7 and increased from Day 7 to 9 (P < 0.05) in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group. Plasma progesterone concentrations in the Ovsynch group with low IGF-I concentrations on Day 0 were higher on Day 14 than in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group (P < 0.05). In conclusion, CIDR-based protocols may improve conception relative to Ovsynch in early postpartum beef cows with lower plasma IGF-I concentrations at the start of the protocols. This improvement is probably due to prevention of premature increases of estradiol-17beta and progesterone concentrations, which occurred in cows with low IGF-I concentrations treated with Ovsynch, by the CIDR treatment.

Summer heat stress alters the mRNA expression of selective-uptake and endocytotic receptors in bovine ovarian cells

Summer heat stress (HS) is a major factor in decreased reproductive performance in high-producing dairy cattle, possibly by affecting the steroidogenic capacity of ovarian follicles and ovarian follicular dynamics. In the present study, mRNA expression of cholesterol receptors was determined in bovine ovarian cells. Two endocytotic receptors (very-low-density lipoprotein receptor (VLDLr) and low-density lipoprotein receptor (LDLr)), and two selective-uptake receptors (scavenger receptor class B type 1 receptor (SRB1) and the lipoprotein-receptor-related protein 8 (LRP8)) were evaluated. Ovarian follicles in four diameter categories were evaluated from cows under non-heat stress (NHS) and HS conditions. As follicle size increased, expression of mRNA in NHS cows increased for the selective-uptake receptors, SRB1 and LRP8, and decreased (P<0.004) for the endocytotic receptors, LDLr and VLDLr. In contrast, in HS cows, mRNA expression did not significantly change (with increasing follicle diameter) for either receptor type. With increasing follicle diameter, cholesterol and fatty acid concentrations in the follicular fluid did not change in HS cows, whereas in NHS cows, cholesterol increased (P<0.008) and fatty acid decreased (P<0.0001). These changes paralleled those in the different lipoprotein fractions in the follicular fluid. In follicles from HS cows, the altered mRNA expression patterns for the endocytotic and selective-uptake receptors caused changes in the regulation of cholesterol supply at critical stages of folliculogenesis, which may play a role in the low turnover rates of ovarian follicles during the summer.

Follicular dynamics and concentrations of steroids and gonadotropins in lactating cows and nulliparous heifers

Differences in follicular development and circulating hormone concentrations, between lactating cows and nulliparous heifers, that may relate to differences in fertility between the groups, were examined. Multiparous, cyclic, lactating Holstein cows (n=19) and cyclic heifers (n=20) were examined in the winter, during one estrous cycle. The examinations included ultrasound monitoring and daily blood sampling. Distributions of two-wave and three-wave cycles were similar in the two groups: 79 and 21% in cows, 70 and 30% in heifers, respectively. Cycle lengths were shorter by 2.6 days in heifers than in cows, and in two-wave than in three-wave cycles. The ovulatory follicle was smaller in heifers than in cows (13.0+/-0.3 mm versus 16.5+/-0.05 mm). The greater numbers of large follicles in cows than in heifers corresponded well to the higher concentrations of FSH in cows. The duration of dominance of the ovulatory follicle tended to be longer in cows than in heifers. Estradiol concentrations around estrus and the preovulatory LH surge were higher in heifers than in cows (20 versus 9 ng/ml). Progesterone concentrations were higher in heifers than in cows from Day 3 to Day 16 of the cycle. Circulating progesterone did not differ between two-wave and three-wave cycles. The results revealed differences in ovarian follicular dynamics, and in plasma concentrations of steroids and gonadotropins; these may account for the differences in fertility between nulliparous heifers and multiparous lactating cows.

Effects of GnRH administered to cows at the onset of estrus on timing of ovulation, endocrine responses, and conception

Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 microg of GnRH, or 10 microg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of < or = 30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated < or = 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.

Seasonal differences in progesterone production by luteinized bovine thecal and granulosa cells

This study examined seasonal differences in progesterone (P4) production by granulosa cells (GC) and thecal cells (TC) that were luteinized in vitro during the winter or the summer; it also compared plasma P4 concentrations of lactating dairy cows in the two seasons. First-wave dominant follicles obtained from Holstein cows were dissected on day 6 of the cycle, GC and TC were separated, enzymatically dispersed, and cultured for 9 days in media containing 1% fetal calf serum, forskolin (10 micromol/mL) and insulin (2 microg/mL), to induce cell luteinization. All experimental procedures were identical and characteristics of the follicles were similar in the two seasons. During 9 days of culture, P4 production by luteinized GC was higher in winter than in summer, but the difference only tended to be significant. In contrast, luteinized TC produced three times as much P4 in winter as in summer (324 versus 100 ng/10(5)cells). In the in vivo experiment, P4 concentrations in plasma collected during entire estrous cycles in winter and summer were compared. The cows were, on average, at 70 days postpartum and yielded similar amounts of milk. Concentrations of progesterone in plasma were significantly higher in winter than in summer; during the mid-luteal phase the difference between the two seasons was 1.5 ng/mL. These results indicate that chronic effects of heat-stress are possibly carried over from an impaired follicle to an impaired corpus luteum (CL), and that luteinized TC are more susceptible to heat-stress than luteinized GC.

Two methods of inducing low plasma progesterone concentrations have different effects on dominant follicles in cows

The effects of two methods of inducing low progesterone concentrations on the shape of the plasma progesterone curve and on follicular characteristics in lactating cows were studied. A low ascending progesterone curve was elicited by three PGF2alpha injections on d 3 to 4 of the estrous cycle; a low constant curve by induction of corpus luteum regression on d 6 and insertion of two progesterone-containing intravaginal devices from d 6 to 15 of the cycle. Plasma progesterone concentration was highest in the untreated control group, intermediate in low ascending group, and lowest in the low constant group. On d 15, both control and low ascending groups had one large healthy and one large atretic follicle, suggesting a turnover of follicular waves; in the low constant group, the presence of only one very large healthy follicle indicated follicular persistence. Estradiol concentration in the follicular fluid and its production by granulosa cells were highest in the low constant, intermediate in the low ascending, and lowest in the control group. Androstenedione concentration in the follicular fluid and its production by theca cells were higher in the low constant than in the low ascending and control groups. The results indicate that the low ascending progesterone curve affected follicular development and steroidogenesis differently from the low constant curve. We suggest that the low ascending curve mimics the effects of naturally occurring low plasma progesterone concentrations better, and it might, therefore, be used as a model for studying the effects of low plasma progesterone on fertility.

Estrus synchronization of lactating dairy cows with GnRH, progesterone, and prostaglandin F2 alpha

The reproductive performance of synchronized cows was compared with that of nonsynchronized cows. In trial 1, cyclic cows in five seasonal herds were randomly divided into two groups. Cows in one group (n = 515) were treated with a GnRH agonist and an intravaginal progesterone device, followed in 7 d by a PGF2 alpha injection, and the device was removed 1 d after PGF2 alpha. Cows in the other group (n = 512) did not receive any treatment and acted as control. In trial 2, the treatments were similar to those used in trial 1 except that the progesterone device was removed at the time of PGF2 alpha injection (synchronized: n = 516; control: n = 512). The estrus synchronization rate was 92.8% in trial 1 and 92.2% in trial 2. Conception rate to first artificial insemination (AI) was lower for synchronized cows than for control cows in trial 1 (56.5 vs. 62.7%), but similar in trial 2 (64.6 vs. 63.3%). Across both trials, the pregnancy rate during the AI breeding period was greater for the synchronized cows (85.6%) than for the control cows (81.2%). The synchronization treatment reduced the interval from start of the breeding season to conception for cows conceiving by AI (8.9 vs. 14.8 d) or by AI or natural mating (14.1 vs. 21.6 d). The synchronization protocol used in trial 2 achieved better conception rate than that used in trial 1, but the precision of estrus was less in trial 2 than in trial 1.