Importance of preovulatory estradiol on uterine receptivity and luteal function

Animals that exhibited estrus had greater pregnancy success compared to animals that did not exhibit estrus before fixed-time AI (FTAI). Estradiol is synthesized in bovine ovarian follicles under gonadotropin regulation and can directly and indirectly regulate the uterine receptivity and luteal function. Estradiol concentrations at FTAI impacted oviductal gene expression and has been reported to play an important role in establishing the timing of uterine receptivity. These changes have been reported to impact uterine pH and sperm transport to the site of fertilization. After fertilization, preovulatory estradiol has been reported to improve embryo survival likely by mediating changes in uterine blood flow, endometrial thickness and changes in histotroph. Cows with greater estradiol concentrations at the time of GnRH-induced ovulation also had a larger dominant follicle size and greater circulating progesterone concentrations on day 7. Therefore, it is impossible to accurately determine the individual benefit of greater estradiol concentrations prior to ovulation and greater progesterone concentrations following ovulation to pregnancy establishment, as these two measurements are confounded. Research has indicated an importance in the occurrence and timing of increasing preovulatory concentrations of estradiol, but increasing estradiol concentrations by supplementation may not be sufficient to increase fertility. Increased production of estradiol by the preovulatory follicle may be required to enhance fertility through the regulation of sperm transport, fertilization, oviductal secretions, the uterine environment, and embryo survival.

RNA sequencing and iTRAQ proteomic data from an experiment examining the influence of conceptus presence and preovulatory estradiol on endometrial gene transcripts and proteins around maternal recognition of pregnancy in beef cattle

RNA sequencing reads and isobaric tags for a relative and absolute quantification (iTRAQ)-Based Proteomic Data were used to determine the impact of conceptus presence and preovulatory estradiol concentration on function of the d16 uterus in beef cattle. Conceptuses and endometrial biopsies were collected from the uterine horn ipsilateral to the corpus luteum. Total cellular RNA was extracted from endometrium for RNA sequencing across two lanes of a NovaSeq S2, 2 × 50-bp run. Two independent uterine luminal fluid pools (ULF) were made for each group: highE2/conceptus, highE2/noconceptus, lowE2/conceptus, and lowE2/noconceptus. Peptides were labeled with iTRAQ reagents and analyzed using 2-dimensional liquid chromatography mass spectrometry. Transcript abundances were determined using DESeq2 (FDR <0.05, FC>2). Scaffold Q+ was used to quantitate peptide and protein identifications in ULF. Datasets include uterine transcript and protein abundances among highE2/conceptus vs highE2/noconceptus and lowE2/conceptus vs lowE2/noconceptus groups. This information can be useful for further investigating the role of specific transcripts and proteins in the maintenance of early pregnancy in beef cattle. This dataset is related to the article ‘Influence of conceptus presence and preovulatory estradiol exposure on uterine gene transcripts and proteins around maternal recognition of pregnancy in beef cattle’ by E.J. Northrop-Albrecht, J.J.J. Rich, R.A. Cushman, R. Yao, X. Ge, G.A. Perry. Molecular and Cellular Endocrinology.

Effects of Pre-Synchronization With Prostaglandin F2α and a Progestin, and Delayed Insemination on Pregnancy Rates With Sexed Semen in Replacement Beef Heifers

To determine the effects of pre-synchronization and delayed fixed-time artificial insemination (TAI) on pregnancy rates (PR/AI) with sexed semen, 1,844 beef heifers were enrolled in a completely randomized design at 12 locations. Within a location, the heifers were randomly assigned to one of the five treatments: (1 and 2), heifers were administered prostaglandin F2α (PGF) on Day -7, gonadotropin-releasing hormone (GnRH), and a controlled internal drug releasing (CIDR) insert on Day 0, PGF at CIDR removal on Day 7, and a second injection of GnRH at TAI 72 h later with either conventional (CTRL72-CNV) or sexed semen (CTRL72-SEX); (3 and 4), treated the same as CTRL72 but received a CIDR insert on Day -7 at PGF administration and TAI at 60 h with either conventional (CIDR60-CNV) or sexed semen (CIDR60-SEX); (5), treated the same as CIDR60 but had TAI delayed to 72 h with sexed semen (CIDR72-SEX). Estrus detection patches were applied to all heifers on Day 7 and were evaluated for activation at TAI. Estrus expression did not differ (p = 0.92) between CIDR60 and CIDR72 heifers, but was greater (p &lt; 0.001) in CIDR60 and CIDR72 heifers compared with CTRL72 heifers. Among treatments, PR/AI differed (p &lt; 0.001) and were greater (p ≤ 0.003) in CTRL72-CNV and CIDR60-CNV heifers than CIDR60-SEX and CIDR72-SEX heifers (51.6 and 48.1 vs. 37.5 and 25.3%, respectively). In addition, PR/AI were greater (p &lt; 0.001) in CTRL72-SEX and CIDR60-SEX heifers when compared with CIDR72-SEX (42.0 and 37.5 vs. 25.3%, respectively) heifers but only tended (p = 0.09) to differ between CTRL72-SEX and CIDR60-CNV heifers. No differences (p = 0.33) were determined between CTRL72-CNV and CIDR60-CNV or between CTRL72-SEX and CIDR60-SEX heifers (p = 0.22). In conclusion, no differences were determined between heifers pre-synchronized with only PGF and those pre-synchronized with PGF and a CIDR insert when inseminated with either conventional or sexed semen. Therefore, the use of a CIDR insert for an additional 7 days was not beneficial to PR/AI when heifers were TAI at 60 h with either conventional or sexed semen. Furthermore, delaying TAI to 72 h with sexed semen after pre-synchronization with both PGF and a CIDR insert had a negative impact on PR/AI.

Influence of conceptus presence and preovulatory estradiol exposure on uterine gene transcripts and proteins around maternal recognition of pregnancy in beef cattle

The uterine environment must provide sufficient endocrine conditions and nutrients for pregnancy maintenance and conceptus survival. The objective of this study was to determine the effects of preovulatory estradiol and conceptus presence on uterine transcripts and uterine luminal fluid (ULF) proteins. Beef cows/heifers were synchronized and artificially inseminated (d 0). Uteri were flushed (d 16); conceptuses and endometrial biopsies were collected. Total cellular RNA was extracted from endometrium for RNA sequencing and RT-PCR validation. There were two independent ULF pools made for each of the following groups: highE2/conceptus, highE2/noconceptus, lowE2/conceptus, and lowE2/noconceptus that were analyzed using the 2D LC-MS/MS based iTRAQ method. There were 64 differentially expressed genes (DEGs) and 77 differentially expressed proteins (DEPs) in common among the highE2/conceptus vs highE2/noconceptus and lowE2/conceptus vs lowE2/noconceptus groups. In summary, the interaction between preovulatory estradiol and the conceptus induces the expression of genes, proteins, and pathways necessary for pregnancy.

Association between length of proestrus, follicular size, estrus behavior, and pregnancy rate in beef heifers subjected to fixed-time artificial insemination

This study evaluated the relationship between proestrus length and follicular size, estrous behavior, and pregnancy rate in Bos taurus beef heifers subjected to fixed-time artificial insemination (FTAI). A total of 911 heifers received a synchronization treatment protocol for FTAI (J-Synch) consisting of an intravaginal progesterone device for 6 d, estradiol benzoate at the time of device insertion cloprostenol sodium and eCG at device removal and GnRH at the time of FTAI. The presence or absence of a corpus luteum (CL) was determined by ultrasonography at device insertion and all heifers were tail painted at device removal for estrus detection at the time of FTAI. For the establishment of different periods of proestrus length (i.e., interval from device removal to FTAI), GnRH was administered i.m. at 48 h (n = 308), 60 h (n = 290) or 72 h (n = 313) after device removal. The diameter of the largest follicle at the time of GnRH administration was determined by ultrasonography, expression of estrous was determined by percentage of tail paint removal, and FTAI was performed at the time of GnRH administration in all heifers. The diameter of the largest follicle was greater when GnRH/FTAI was performed at 72 or 60 h (12.9 ± 0.2 mm and 12.8 ± 0.1 mm, respectively) than at 48 h (12.2 ± 0.1 mm, P < 0.05). The proportion of heifers in estrus tended to be greater when GnRH/FTAI was performed at 72 h (77.0%, 137/178) than at 48 h (68.2%, 122/179; P = 0.06), and intermediate at 60 h (71.4%, 120/168). Pregnancy rate tended to be greater in heifers with the longest (72 h: 70.0%, 219/313) than the shortest (48 h: 63.6%, 196/308; P < 0.1) proestrus length, while 60 h proestrus length was intermediate (63.1%, 183/290; P= NS). Pregnancy rate was affected by the presence of a CL at device insertion (71.3%, 352/494 in heifers with a CL, vs. 59.0%, 246/417 for those without a CL; P < 0.01). For those heifers bearing a CL, pregnancy rate was greater in heifers with a 72 h proestrus length (77.0%, 134/174) than with 48 or 60 h proestrus length (67.7%, 107/158 and 68.5%, 111/162; respectively; P < 0.05). In heifers without a CL, proestrus length did not affect pregnancy rate. In summary, extending proestrus length by delaying the interval from device removal to GnRH/FTAI from 48 to 72 h, was associated with a greater diameter of the preovulatory follicle, greater proportion of heifers expressing estrus at the time of FTAI, and greater pregnancy rate in cycling beef heifers.

Influence of estradiol on bovine trophectoderm and uterine gene transcripts around maternal recognition of pregnancy†

Embryo survival and pregnancy success is increased among animals that exhibit estrus prior to fixed time-artificial insemination, but there are no differences in conceptus survival to d16. The objective of this study was to determine effects of preovulatory estradiol on uterine transcriptomes, select trophectoderm (TE) transcripts, and uterine luminal fluid proteins. Beef cows/heifers were synchronized, artificially inseminated (d0), and grouped into either high (highE2) or low (lowE2) preovulatory estradiol. Uteri were flushed (d16); conceptuses and endometrial biopsies (n = 29) were collected. RNA sequencing was performed on endometrium. Real-time polymerase chain reaction (RT-PCR) was performed on TE (n = 21) RNA to measure relative abundance of IFNT, PTGS2, TM4SF1, C3, FGFR2, and GAPDH. Uterine fluid was analyzed using 2D Liquid Chromatography with tandem mass spectrometry-based Isobaric tags for relative and absolute quantitation (iTRAQ) method. RT-PCR data were analyzed using the MIXED procedure in SAS. There were no differences in messenger RNA (mRNA) abundances in TE, but there were 432 differentially expressed genes (253 downregulated, 179 upregulated) in highE2/conceptus versus lowE2/conceptus groups. There were also 48 differentially expressed proteins (19 upregulated, 29 downregulated); 6 of these were differentially expressed (FDR < 0.10) at the mRNA level. Similar pathways for mRNA and proteins included: calcium signaling, protein kinase A signaling, and corticotropin-releasing hormone signaling. These differences in uterine function may be preparing the conceptus for improved likelihood of survival after d16 among highE2 animals.

Short communication: Greater intensity of estrous expression is associated with improved embryo viability from superovulated Holstein heifers

The aim of this study was to determine the association between estrous expression, measured using a breeding indicator and an automated activity monitor (AAM), and the success of embryo collection after superovulation. Holstein heifers (n = 51; 10.5 to 14.5 mo, and 325.0 ± 21.1 kg of body weight) were superovulated (n = 69 events) for the collection of embryos using a protocol based on sequential administration of FSH for follicle superstimulation and GnRH to induce ovulation. Artificial insemination (AI) was performed twice, once at the moment of GnRH administration and again 12 h later, using thawed, sexed semen. Ovaries were scanned via ultrasonography on the day of the first AI to count the total number of preovulatory follicles and 7 d later for the total number of corpora lutea present. Embryos were collected 7 d post-AI, counted, and assessed for viability. A breeding indicator (Estrotect, Rockway Inc., Spring Valley, WI) and a collar-mounted AAM (CowScout Activity Monitoring System, GEA, Dusseldorf, Germany) were used to measure standing mounts and an algorithmic estimate of estrous expression, respectively. A score for the breeding indicator was given as follows: score 1 = 100% of the indicator was intact; score 2 = 50% of the indicator was rubbed off; score 3 = greater than 50% of the indicator was rubbed off. Estrous expression detected by the AAM was quantified through the relative increase in physical activity and duration of time spent above a set threshold. Data were analyzed by ANOVA using the MIXED procedures of SAS (SAS Institute Inc., Cary, NC). The number of follicles present at AI was not affected by estrous expression. The mean (± SD) ovulatory response was 67.5 ± 26.3%. We found an effect of estrous expression as detected by the breeding indicator on the ovulatory response (42.1 ± 8.0, vs. 78.2 ± 9.0, vs. 74.0 ± 4.9%, for scores 1, 2, and 3, respectively) but not from the AAM. Heifers that had a score of 3 (versus those with scores of 1 and 2) on the breeding indicator had a greater number of embryos (4.1 ± 0.5, vs. 1.2 ± 1.0, vs. 1.8 ± 1.0 embryos), and a greater percentage of these embryos were viable (43.1 ± 0.05, vs. 35.5 ± 0.1, vs. 34.3 ± 0.1%). Similarly, heifers that showed a greater intensity of activity (as measured by the AAM) had a greater number of embryos collected (10.2 ± 1.2 vs. 6.0 ± 1.3 embryos), and a greater percentage of those embryos were viable (53.1 ± 5.0 vs. 23.4 ± 5.1%). Longer-duration estrus episodes were associated with a higher percentage of viable embryos (51.2 ± 5.2 vs. 25.3 ± 5.3%). In conclusion, stronger estrous intensity was associated with a greater number of total embryos collected and a greater percentage of viable embryos. These results suggest that monitoring the intensity of estrus could be used to predict superovulatory response as well as embryo quality in Holstein heifers.

Influence of Sexcel™ (gender ablation technology) gender-ablated semen in fixed-time artificial insemination of beef cows and heifers

Previous research has indicated that gender-sorted semen has decreased conception rates compared to conventional semen. A new method to skew the gender ratio of semen has been developed that does not use traditional sorting technology. Thus, the objective of this study was to evaluate the use of gender-ablated semen in a fixed-time AI protocol. Beef heifers and cows (n = 878) from six herds were synchronized with the 7-d CO-Synch plus CIDR protocol, and artificially inseminated (AI) after CIDR removal (cows 60-66 h; heifers 52-56 h). Estrus detection aids were applied at CIDR removal and estrus activity was determined at time of AI. Animals remained separated from bulls for at least 10 d after AI. Pregnancy success and fetal age were determined between d 28 and 70 after AI. Semen from five sires was utilized in this study, with two sires used in each herd. Sire 1 was used in all herds and the use of the second sire varied by herd (both conventional and gender-ablated semen from each sire was used in each herd). Data were analyzed using the GLIMMIX procedure in SAS and included the influence of semen type, estrus expression, semen type by estrus expression, dam age, and sire in the model. Herd was included as a random variable. Overall, conventional semen had greater conception rates compared to gender-ablated semen (P < 0.01; 67% vs 52%), and cows that had fully activated patches and partially activated patches had greater conception rates compared to animals that had not exhibited estrus (P < 0.01; 69%, 65%, and 45%). There was no semen type by estrus expression interaction (P = 0.24). Conception rates tended to be greater for conventional semen among animals that had activated patches (P = 0.06; 73% vs 65%) and partially activated patches (P = 0.06; 72% vs 59%). Conception rates were greater for conventional semen (P < 0.01; 56% vs 33%) among animals that did not exhibit estrus. There was no effect of dam age (P = 0.40) or sire (P = 0.92) on conception rates. In conclusion, Sexcel™ gender-ablated semen can successfully be used in fixed-time AI protocols among animals that exhibit estrus, but caution should be used among animals that do not exhibit estrus.

Estrous expression during a fixed-time artificial insemination protocol enhances development and interferon-tau messenger RNA expression in conceptuses from Bos indicus beef cows

Expression of estrus (EST) near the time of fixed-time artificial insemination (FTAI) increases pregnancy success in beef females. This outcome has been associated with improved pregnancy establishment and maintenance, although research is still warranted to validate this theory. Hence, this experiment compared ovarian, uterine and conceptus factors associated with pregnancy establishment in Bos indicus beef cows according to estrous expression during a FTAI protocol. One hundred lactating multiparous Nelore cows received a 2 mg injection of estradiol benzoate and an intravaginal progesterone (P4) releasing device on day -11, a 12.5 mg injection of prostaglandin F2α on day -4, P4 device removal in addition to 0.6 mg injection of estradiol cypionate and 300 IU injection of equine chorionic gonadotropin on day -2, and FTAI on day 0. An estrous detection patch was attached to the tailhead of each cow on day -2, and estrous expression was defined as removal of >50% of the rub-off coating from the patch at FTAI. Overall, 39 cows expressed EST, 55 did not express EST (NOEST), and six cows lost their patch and were discarded from the experiment. Ovarian ultrasonography was performed at FTAI, and on days 7 and 15 of the experiment. Blood samples were also collected on days 7 and 15. Only cows without a corpus luteum (CL) on day 0, and with a CL on days 7 and 15 remained in the experiment (EST, n=36; NOEST, n=48). On day 15, cows were randomly selected within each group (EST, n=29; NOEST, n=30) for conceptus collection via transcervical flushing, followed by endometrial biopsy in the uterine horn ipsilateral to the CL. Within cows not assigned to conceptus collection, blood samples were collected for whole blood RNA extraction (day 20) and pregnancy status was verified by transrectal ultrasonography (day 30). Diameter of dominant follicle on day 0 and plasma P4 concentrations on day 7 were greater (P⩽0.02) in EST v. NOEST cows. Conceptus length and messenger RNA (mRNA) expression of prostaglandin E synthase and interferon-tau were greater (P⩽0.04) in EST v. NOEST cows. Moreover, EST cows diagnosed as pregnant on day 30 had greater (P<0.01) blood mRNA expression of myxovirus resistance 2 on day 20 compared with NOEST. In summary, estrous expression near the time of FTAI enhanced pregnancy establishment factors in B. indicus cows, including conceptus development and mRNA expression of interferon-tau.

Influence of GnRH supplementation at CIDR removal on estrus expression and interval to estrus in beef cattle

Previous research has indicated that multiple small doses of GnRH following CIDR removal increased circulating concentrations of estradiol. Therefore, our objective was to determine if a single small dose of GnRH (5 μg or 10 μg) at CIDR removal would impact expression of estrus and/or interval to estrus. Beef cows and heifers (n = 1620; n = 1057 cows, n = 563 heifers) were synchronized using the 7-day CO-Synch + CIDR protocol, and randomly assigned to one of three treatments (0, 5, or 10 μg of a GnRH analog at CIDR removal). Animals were inseminated following detection in estrus. Interval to estrus was calculated for each animal that exhibited estrus (INTERVAL 1). Animals that did not exhibit estrus were administered 100 μg of GnRH at the time of AI and their interval to estrus was designated at 120 h (INTERVAL 2). There was a treatment by age interaction (P = 0.05) on INTERVAL 1. Heifers treated with 5 μg of GnRH tended to have a shorter interval to estrus (P = 0.07; 47 ± 1.4 h) compared to 0 μg (50 ± 1.5 h) and did have a shorter interval compared to 10 μg (P < 0.01; 52 ± 1.5 h). There were no differences between treatments in interval to estrus among cows (P > 0.34). When animals that did not exhibit estrus by 120 h were included in the analysis there was no treatment by age interaction (P = 0.49). This is likely due to the fact that treatment (P < 0.01), but not age (P = 0.96) or treatment by age (P = 0.74) influenced expression of estrus. In addition, there tended to be a treatment by estrus interaction (P = 0.08) on pregnancy success. There was no difference in pregnancy success between treatments among animals that exhibited estrus (P > 0.30). In summary, 5 μg of GnRH at CIDR removal tended to decrease the interval to estrus and increased expression of estrus among heifers but not cows, and 10 μg of GnRH at CIDR removal did not improve estrus expression and lengthened the interval to estrus in comparison to the control.

Impacts of estrus expression and intensity during a timed-AI protocol on variables associated with fertility and pregnancy success in Bos indicus-influenced beef cows

This experiment evaluated the impacts of estrus expression and intensity, estimated by physical activity during a timed-AI protocol, on reproductive performance of Bos indicus-influenced beef cows. A total of 290 lactating, primiparous, and multiparous nonpregnant Nelore × Angus cows received a 2 mg injection of estradiol benzoate and an intravaginal progesterone (P4) releasing device (CIDR) on d -11, a 12.5 mg injection of PGF2α on d -4, CIDR removal in addition to 0.6 mg injection of estradiol cypionate and 300 IU injection of eCG on d -2, and timed-AI on d 0. Cows were fitted with a pedometer behind their left shoulder on d -4. An estrus detection patch was attached to the tail-head of each cow on d -2. Pedometer results were recorded on d -2 and 0. Estrus expression was defined as removal of >50% of the rub-off coating from the patch on d 0. Net physical activity during estrus was calculated by subtracting total steps from d -4 to -2 (nonestrus basal activity) from total steps from d -2 to 0 (proestrus + estrus period) of each cow. Cows that did not express estrus were classified as NOESTR. Cows that expressed estrus were ranked by net physical activity; those above the median were classified as HIESTR and the remaining cows as LWESTR. Ovarian ultrasonography was performed on d 0 and 7. Blood was collected on d 0, 7, 20, and 30. Pregnancy status was verified by ultrasonography on d 30. Only data from cows responsive to the estrus synchronization protocol were utilized (NOESTR, n = 59; LWESTR, n = 100; HIESTR, n = 98). Diameter of dominant follicle on d 0, corpus luteum volume on d 7, and plasma P4 concentrations on d 7 were greater (P ≤ 0.05) in HIESTR vs. LWESTR and NOESTR and also greater (P ≤ 0.05) for LWESTR vs. NOESTR. Plasma P4 concentrations on d 0 were greater (P < 0.01) in NOESTR vs. HIESTR and LWESTR and similar (P = 0.93) between HIESTR and LWESTR. Whole blood mRNA expression of myxovirus resistance 2 on d 20 was greater (P ≤ 0.05) in HIESTR vs. LWESTR and NOESTR, and similar (P = 0.72) between LWESTR and NOESTR. Pregnancy rates were less (P ≤ 0.04) in NOESTR vs. HIESTR and LWESTR (52.4%, 68.9%, and 73.5%, SEM = 7.2), and similar (P = 0.57) between HIESTR and LWESTR. Hence, expression of estrus during a timed-AI protocol improved ovarian dynamics and pregnancy success, whereas estrus intensity modulated key biological markers associated with fertility but not pregnancy rates in B. indicus-influenced cows beef cows.

Effects of extending the length of pro-oestrus in an oestradiol- and progesterone-based oestrus synchronisation program on ovarian function, uterine environment and pregnancy establishment in beef heifers

The aim of the present study was to investigate the effects of a strategy for extending pro-oestrus (the interval between luteolysis and ovulation) in an oestrus synchronisation protocol (named J-Synch) in beef heifers on follicular growth, sexual steroid concentrations, the oestrogen receptor ERα and progesterone receptors (PR) in the uterus, insulin-like growth factor (IGF) 1 and pregnancy rates. In Experiment 1, heifers treated with the new J-Synch protocol had a longer pro-oestrus period than those treated with the conventional protocol (mean (± s.e.m.) 93.7 ± 12.9 vs 65.0 ± 13.7 h respectively; P < 0.05). The rate of dominant follicle growth from the time of progesterone device removal to ovulation was greater in heifers in the J-Synch than conventional group (P < 0.05). Luteal area and serum progesterone concentrations were greater in the J-Synch Group (P < 0.05) for the 12 days after ovulation. Progesterone receptor (PGR) staining on Day 6 after ovulation in the uterine stroma was lower in the J-Synch than conventional group (P < 0.05), and the expression of PR gene (PGR) and IGF1 gene tended to be lower in J-Synch-treated heifers (P < 0.1). In Experiment 2 (n = 2349), the pregnancy rate 30–35 days after fixed-time AI (FTAI) was greater for heifers in the J-Synch than conventional group (56.1% vs 50.7% respectively). In conclusion, our strategy for extending pro-oestrus (i.e. the J-Synch protocol) significantly improves pregnancy establishment in beef heifers. This improvement was related to an increased rate of growth of the dominant ovulatory follicle, greater progesterone concentrations during the ensuing luteal phase and different uterine patterns of PGR and IGF1, which may have favoured embryo development and pregnancy establishment.

Using estrus detection patches to optimally time insemination improved pregnancy risk in suckled beef cows enrolled in a fixed-time artificial insemination program

A multilocation study examined pregnancy risk (PR) after delaying AI in suckled beef cows from 60 to 75 h when estrus had not been detected by 60 h in response to a 7-d CO-Synch + progesterone insert (CIDR) timed AI (TAI) program (d -7: CIDR insert concurrent with an injection of GnRH; d 0: PGF injection and removal of CIDR insert; and GnRH injection at TAI [60 or 75 h after CIDR removal]). A total of 1,611 suckled beef cows at 15 locations in 9 states (CO, IL, KS, MN, MS, MT, ND, SD, and VA) were enrolled. Before applying the fixed-time AI program, BCS was assessed, and blood samples were collected. Estrus was defined to have occurred when an estrus detection patch was >50% colored (activated). Pregnancy was determined 35 d after AI via transrectal ultrasound. Cows ( = 746) detected in estrus by 60 h (46.3%) after CIDR removal were inseminated and treated with GnRH at AI (Control). Remaining nonestrous cows were allocated within location to 3 treatments on the basis of parity and days postpartum: 1) GnRH injection and AI at 60 h (early-early = EE; = 292), 2) GnRH injection at 60 h and AI at 75 h (early-delayed = ED; = 282), or 3) GnRH injection and AI at 75 h (delayed-delayed = DD; = 291). Control cows had a greater ( < 0.01) PR (64.2%) than other treatments (EE = 41.7%, ED = 52.8%, DD = 50.0%). Use of estrus detection patches to delay AI in cows not in estrus by 60 h after CIDR insert removal (ED and DD treatments) increased ( < 0.05) PR to TAI when compared with cows in the EE treatment. More ( < 0.001) cows that showed estrus by 60 h conceived to AI at 60 h than those not showing estrus (64.2% vs. 48.1%). Approximately half (49.2%) of the cows not in estrus by 60 h had activated patches by 75 h, resulting in a greater ( < 0.05) PR than their nonestrous herd mates in the EE (46.1% vs. 34.5%), ED (64.2% vs. 39.2%), and DD (64.8% vs. 31.5%) treatments, respectively. Overall, cows showing estrus by 75 h (72.7%) had greater ( < 0.001) PR to AI (61.3% vs. 37.9%) than cows not showing estrus. Use of estrus detection patches to allow for a delayed AI in cows not in estrus by 60 h after removal of the CIDR insert improved PR to TAI by optimizing the timing of the AI in those cows.

Influence of post-insemination nutrition on embryonic development in beef heifers

Previous studies have demonstrated that a decrease in nutrition immediately following AI reduces pregnancy success in beef heifers. The objective of this experiment was to determine if nutrient restriction following AI impacted early embryonic development among non-super ovulated heifers. Beef heifers in eight replications (Rep; Rep 1; n = 14, Rep 2; n = 15, Rep 3; n = 15, Rep 4; n = 14, Rep 5; n = 15, Rep 6; n = 15, Rep 7; n = 25, Rep 8; n = 25) across two locations (UMN, SDSU) were developed in a dry-lot and fed 125% NRC requirements from weaning to timed-AI (d 0). Heifers were timed-AI to a single sire in all replications. Immediately following AI, heifers were assigned, based on age, weight, and estrous response to one of two post-AI nutritional treatments. Half the heifers in each replication continued on the pre-insemination diet, serving as the control treatment (CON) and the remaining heifers were restricted to a sub-maintenance diet (RES). At UMN, heifers in the RES treatment were fed the same diet, but intake was limited to 80% NE_m, while at SDSU, DMI remained the same, but diet composition was altered with the addition of straw to reduce NE_m to 50% of requirements. On d 6, single embryos were collected nonsurgically and recovered embryos (CON; n = 46, RES; n = 42) were evaluated to determine quality (grade 1-9) and stage (1-4). Embryos were then stained and evaluated to determine the number of dead cells and total blastomeres. In Reps 1 through 6, concentrations of IGF-1 were assessed on d 0 and 6 and progesterone concentrations on d 4 and 6. Data were analyzed using the Mixed procedures of SAS. There were no treatment by Rep or treatment by location interactions for any embryo parameter evaluated, thus all data were pooled. Embryo stage and quality were improved (P < 0.01) in the CON (4.4 ± 0.16, 2.2 ± 0.19, respectively) compared to RES treatment (3.7 ± 0.16, 2.9 ± 0.19, respectively). Embryos in the CON treatment had greater total blastomeres (66.9 ± 5.05; P < 0.01) and tended to have a greater percentage of live cells (P < 0.10; 80.9 ± 4.19%) compared to RES (47.9 ± 5.41; 69.7 ± 4.39%, respectively). Progesterone and IGF-1 concentrations did not differ between treatments. In summary, nutrient restriction for 6 days immediately following AI resulted in poorer quality embryos that were delayed in stage of development, suggesting that immediate changes in nutritional status after insemination can alter early embryonic development.

Changes in ovarian function associated with circulating concentrations of estradiol before a GnRH-induced ovulation in beef cows

These studies were conducted to evaluate causes for differences in circulating concentrations of estradiol before a GnRH-induced ovulation. Beef cows were synchronized by an injection of GnRH on day -7 and an injection of prostaglandin F2α (PGF2α) on day 0. In experiment 1, blood samples were collected every 3 h from PGF2α on day 0 to hour 33 after PGF2α and at slaughter (hour 36 to 42; n = 10). Cows were assigned to treatment group based on circulating concentrations of estradiol (E2): HighE2 vs LowE2. At slaughter, follicular fluid (FF) and granulosa cells were collected from the dominant follicle. In experiment 2, blood samples (n = 30) were collected every 8 h from PGF2α until the dominant follicle was aspirated via ultrasound-guided follicular aspiration to collect FF and granulosa cells (hour 38 to 46). In experiment 1, HighE2 had increased abundance of 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.02), and greater concentrations of estradiol and androstenedione (P ≤ 0.02) in the FF. In experiment 2, HighE2 had increased abundance of CYP11A1, 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.03) vs either LowE2 or GnRHLowE2. There was a tendency (P = 0.07) for LH pulse frequency to be increased in both the GnRHLowE2 and HighE2 compared with LowE2. HighE2 cows experienced increas in circulating concentrations of estradiol compared with LowE2. In conclusion, animals with greater concentrations of circulating estradiol before fixed-time AI experienced an upregulation of the steroidogenic pathway during the preovulatory period.

Expression of Na(+)/H(+) exchanger isoforms 1, 2, 3, and 4 in bovine endometrium and the influence of uterine pH at time of fixed-time AI of pregnancy success

Cows that exhibit estrus prior to fixed-time AI had increased sperm transport to the site of fertilization, and improved embryo quality on d 6 after insemination. Sperm transport is influenced by uterine pH, and research has reported that uterine pH decreased at onset of estrus, but must return to normal prior to ovulation. Therefore, the objectives of these studies were to investigate a possible mechanism for the regulation of uterine pH around the onset of estrus, and to determine if uterine pH at time of fixed-time AI influenced pregnancy success. In experiment 1, Angus-cross beef cows (n=40 and 28 in rep. 1 and 2, respectively) were synchronized with the PG 6-day CIDR protocol (PGF2α on d -9, GnRH and insertion of a CIDR on d -6, and PGF2α and CIDR removal on d 0). Cows were blocked by follicle size at time of CIDR removal, and uterine biopsies were collected at 0, 12, 24, 36, 48, 60 (Rep. 1), 72, 84, or 96h (Rep2) after CIDR removal, and total cellular RNA was extracted from all biopsies. Estrus was monitored by the HeatWatch Estrous Detection System. In experiment 2, 223 postpartum beef cows in 2 herds were synchronized with a fixed-time AI protocol (herd 1: n=97; CO-Synch plus CIDR protocol; herd 2: n=126; Co-synch protocol). Uterine pH was determined at time of AI (n=80 and 63 for herd 1 and 2, respectively), and estrus was monitored by visual estrus detection with the aid of an ESTROTECT estrous detection patches, and pregnancy was determined by transrectal ultrasonography. In experiment 1, there was a significant (P<0.01), quadratic relationship in expression of Na(+)/H(+) exchanger isoforms 1, 2, and 3 among animals that exhibited estrus, with expression greatest at time of CIDR removal, decreasing to the onset of estrus, and then increasing again following the onset of estrus. Among cows that did not exhibit estrus, the preceding relationship did not exist (P>0.46). In experiment 2, cows that had initiated estrus prior to fixed-time AI had decreased (P=0.01) uterine pH compared to cows that did not initiate estrus (6.78±0.03 and 6.89±0.03, respectively), and uterine pH at AI had an approximately linear effect on pregnancy success within the observed pH range. Furthermore, cows that initiated estrus prior to AI had increased (P=0.05) pregnancy success (52% vs. 38%) compared to cows that had not initiated estrus. In summary, expression of Na(+)/H(+) exchanger isoforms 1, 2, and 3 decreased after CIDR removal among cows that exhibited estrus, but did not change among cows that did not exhibit estrus. Additionally, as uterine pH decreased pregnancy success tended to increase (P=0.076, logistics regression). Thus, Na(+)/H(+) exchanger isoforms 1, 2, and 3 appear to be key regulators of uterine pH around the onset of estrus, and this change in uterine pH is critical for pregnancy success.

SUMMARY SENTENCE

Expression of Na(+)/H(+) exchanger isoforms 1, 2, and 3 decreased after CIDR removal among cows that exhibited estrus, but did not change among cows that did not exhibit estrus, and as uterine pH decreased, pregnancy success tended to increase.