Comparison of follicular dynamics and hormone concentrations between the 7-day and 5-day CO-Synch + CIDR program in primiparous beef cows

Early induction of luteolysis in a timed AI protocol increases reproductive performance in beef cows

The aim of this study was to produce a longer proestrus by early administration of prostaglandin F2α (PGF) in a timed artificial insemination (TAI) protocol in non-suckling Bos taurus (Angus crossbreed) beef cows. On day 0, cows (n = 489) were treated with an intravaginal 1 g progesterone (P4) device and 2 mg of estradiol benzoate. On day 7, cows were randomized into two groups: PGF7(n = 244; 500 µg of sodium cloprostenol 24 h before P4 device removal) or PFG8 (n = 245; 500 µg of sodium cloprostenol at P4 device removal). On day 8, P4 device was removed and cows received 0.5 mg of estradiol cypionate. All cows were submitted to TAI on day 10 (48-50 hours after P4 device removal). Cows treated with PGF on day 7 had greater expression of estrus (91.3 vs 79.1 %; P = 0.0011), regardless of CL presence at beginning of the protocol. Cows from PGF7 group had lower circulating P4 concentrations on day 8 in comparison with PGF8 treated cows (1.86 vs 2.99 ng/mL; P < 0.001). However, preovulatory follicle diameter did not differ among treatments at TAI (11.9 vs 11.8 mm; P = 0.7881). Pregnancy per TAI (P/TAI) was greater for PGF7 (63.9 vs 50.6 %; P = 0.0114) than PGF8 treated cows. In cows with follicles <8.5 mm at TAI, expression of estrus (33.3 vs 26.6 %; P = 0.6427) and P/TAI (40 vs 26.6 %; P = 0.3657) were low in both PGF7 and PGF8 treated cows, respectively. In cows with medium follicle size (8.5 to 11.9 mm) PGF7 treated cows had greater expression of estrus (90.5 vs 80 %; P = 0.033) and P/TAI (62.2 vs 49 %; P = 0.053). In cows with follicles >12 mm, expression of estrus was greater for PGF7 than PGF8 treated cows (99.1 vs 93.3 %; P = 0.045), however P/TAI did not differ (68.2 vs 59 %; P = 0.149). In cows with P4 < 1.99 ng/mL on day 8, expression of estrus was similar between PGF7 and PGF8 treated cows (92.6 vs 90.4 %; P = 0.53), and P/TAI tended to be greater for PGF7 than PGF8 treated cows (63 vs 52.1 % P = 0.076). However, in cows with P4 > 2 ng/mL PGF7 cows had higher expression of estrus (89 vs 67.5 %; P = 0.0005) and P/TAI (64.8 vs 48.7 %; P = 0.021) than PGF8. Thus, increasing the proestrous period by inducing luteolysis 24 hours earlier than removing the P4 intravaginal device enhanced fertility in non-suckling cyclic beef cows by increasing expression of estrus and P/TAI.

Research on timed AI in beef cattle: Past, present and future, a 27-year perspective

This review aimed to (1) summarize the results from fixed-timed artificial insemination (TAI) fertility studies performed during the last 27 years; (2) compile and evaluate, as examples from the literature base, the direct comparisons made of specific manipulations to synchronization protocols; (3) evaluate the impact of the TAI programs on the reproductive performance during the breeding season, and (4) provide perspective on the future of TAI programs in beef cattle. A search of the literature published from 1995 to 2021 was conducted to identify experiments in which synchronization of ovulation and TAI in beef cattle was performed. The primary outcome of interest was fertility expressed as pregnancies per TAI. The literature included two search engines, the SIS Web of Science and the US National Library of Medicine Institutes of Health through PubMed. After the initial search and screening, a total of 228 manuscripts were selected containing a total of 272,668 TAI. A dramatic increase in the number of publications and TAIs occurred throughout the years. Most of them were from Brazil and United States, followed by Canada, Argentina, Uruguay, and Australia. Two main types of TAI programs were identified: GnRH-based and E2/P4-based protocols. In terms of GnRH-based programs, two variations were evaluated in the present manuscript. First, we evaluated the effect of the progesterone implant during the protocol. The progesterone implant increased pregnancy/TAI (P/TAI) from 44.3 to 54.3%. Second, the use of a second prostaglandin F2α treatment in 5-d CO-synch program increased the P/TAI from 53.2 to 60.9%. In E2/P4-based programs, use of GnRH at TAI increased P/TAI from 54.7 to 59.2% in cows. However, no increase was detected in heifers. Other research showed that use of TAI can increase the overall proportion of the cows pregnant at end of the breeding season and produce earlier calvings compared with bulls. In conclusion, there have been a large number of excellent research studies that have been performed during the last 27 years on TAI in beef cattle. This technology is being utilized successfully in the beef cattle industry. This success is largely because of the valid research that underlies the application of the technology and the economic value of the technology.

Prohibition of hormones in animal reproduction: what to expect and what to do?

As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. The development of Fixed-Time Artificial Insemination (FTAI) protocols at the end of the 20th century has increased exponentially the number of animals inseminated over the last 20 years. The main reasons for this growth were the possibility of obtaining acceptable pregnancy rates without heat detection and, above all, the induction of cyclicity in suckled cows in postpartum anestrus and prepubertal heifers at the beginning of the breeding season. Most FTAI treatments in South America have been based on the use of progesterone (P4) releasing devices and estradiol to synchronize both follicular wave emergence and ovulation, with pregnancy rates ranging from 40 to 60%. These protocols are implemented on a regular basis, allowing producers access to high-quality genetics, and increasing the overall pregnancy rates during the breeding season. In addition, it provided the professionals involved in these programs with a new source of income and the diversification of their practices into activities other than their usual clinical work. Many of these practices are now apparently at risk from restrictions on the use of estradiol by the European Union (EU) and other countries. However, the development of alternative protocols based on GnRH, with P4 devices and eCG and other new products that are not in the market yet will allow us to adapt to the new times that are coming. Logically, the challenge has already been raised and we must learn to use alternative protocols to try to continue increasing the use of this technology in beef and dairy herds. The objective of the present review is to describe the main aspects of banning estradiol in livestock production, the negative impacts on reproductive efficiency, and to present some alternative FTAI protocols for dairy and beef cattle.

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.

Comparison of the 7-day CO-Synch and 8-day estradiol-based protocols for estrus synchronization and timed artificial insemination in suckled Bos taurus cows

Two experiments were conducted to compare, follicle diameter (FD) on Day -1, corpus luteum (CL) area on Day 7, progesterone (P4) concentration on Day 7 and 18, pregnancy per timed artificial insemination (TAI) on Day 30, and pregnancy loss (PL) between Days 30 and 60 after TAI (TAI, Day 0) using two different synchronization protocols. In Experiment 1, Angus cows (n = 1148) were randomly assigned to either 7-d progesterone CO-Synch (7-d CO-Synch) or 8-d progesterone + estradiol (8-d P + ES) synchronization protocols for TAI. On Day -10, cows in the 7-d CO-Synch treatment group (n = 574) received a progesterone-releasing intravaginal device (PIVD; 0.5 g P4) and GnRH (0.105 mg), on Day -3 the PIVD was removed and cows received cloprostenol (0.150 mg), then, on Day 0 (64 h after PIVD removal), cows received GnRH (0.105 mg) and were TAI. On Day -10, cows in the 8-d P + ES treatment group (n = 574) received a PIVD (0.5 g P4) and estradiol benzoate (2.0 mg), on Day -2 the PIVD was removed, and cows received cloprostenol (0.150 mg) and estradiol cypionate (0.5 mg), then, on Day 0 (48 h after PIVD removal), cows were TAI. Pregnancy per TAI was determined on Days 30 and 60. In a subset of cows (7-d CO-Synch, n = 41; 8-d P + ES, n = 40), serum P4 concentration was evaluated on Day 18. In Experiment 2, anestrus (n = 34) and cyclic (n = 34) suckled beef cows were selected and submitted at random on Day -10, to either 7-d CO-Synch or 8-d P + ES treatment groups. Follicle diameter on Day -1, CL area, and serum P4 concentration on Day 7 were determined. In Experiment 1, pregnancy per TAI on Day 30 did not differ (7-d CO-Synch = 48.9%; 8-d P + ES = 45.6%) between treatments but it was greater for cows with BCS ≥5 (P < 0.01). Pregnancy loss between Days 30 and 60 did not differ between treatment groups but tended to be greater in cows with BCS <5.0 (P < 0.1). In a subset of cows, serum P4 concentration on Day 18 did not differ between treatment groups but tended to be lower (P < 0.1) in cows that had PL between Days 30 and 60 compared to cows that had no PL. In Experiment 2, FD tended to be greater (P < 0.1) and CL area was greater (P = 0.05) in anestrus cows from 7-d CO-Synch treatment. In cyclic cows, the treatment did not affect the FD or CL area. In conclusion, there was no difference in pregnancy per TAI on Day 30 and PL between Days 30 and 60 between cows using 7-d CO-Synch + PIVD or 8-d estradiol-based + PIVD protocols for estrus synchronization and TAI.

Effects of two protocols of ovulation synchronization on corpus luteum size and blood flow, progesterone concentration, and pregnancy rate in beef heifers

The objective of this study was to evaluate the effect of 7-day estradiol-progesterone-based [Treat_(C)] and 5-day Co-Synch plus progesterone [Treat_(Co-Sy)] protocols on ovulation time, pre-ovulatory follicle diameter, corpus luteum (CL) size and blood flow, progesterone (P4) concentration and pregnancy rate (PR) in beef heifers. In Experiment 1, a crossover design was applied (n = 9). For Treat_(C), a progesterone intravaginal (PI) device was inserted, plus 2 mg of estradiol benzoate (day 0). On day 7, 500 µg of cloprostenol plus 0.5 mg of estradiol cypionate were administered, and PI was removed. For Treat_(Co-Sy), on day 0, a PI was inserted plus 100 µg gonadotropin-releasing hormone (GnRH). On day 5, PI was removed, plus 500 µg of cloprostenol and 100 µg of GnRH were administered at 69-70 h later. From day one to ovulation day, dominant follicle was evaluated by ultrasonography. On days 4 and 8 post-ovulation, CL was evaluated by color Doppler, and P4 concentration was determined by chemiluminescence. In Experiment 2, a split-plot experimental design was used. Protocols followed were the same as in Experiment 1 [Treat_(C); n = 310 and Treat_(Co-Sy); n = 314]. Heifers were fixed-time artificially inseminated. Pregnancy was determined on day 41. In Experiment 1, the interval between PI removal and ovulation time was different between protocols (P < 0.01). In addition, P4 concentration was related to the CL size (P < 0.001), CL blood flow (P < 0.01) and protocols (P < 0.03). In Experiment 2, PR did not differ between protocols.

GnRH dose at initiation of a 5-day CO-Synch + P4 for fixed time artificial insemination in suckled beef cows

The objective of the present study was to evaluate the effect of GnRH dose administered at initiation (GnRH-1) of a 5-day CO-Synch + P4 protocol on ovulatory response, expression of estrus, and fertility in suckled beef cows. Suckled beef cows (n = 1101) at four locations were randomized to receive either 100 or 200 µg of gonadorelin acetate at initiation (D-8) of a 5-day CO-Synch + P4 protocol concurrently with insertion of an intravaginal progesterone (P4) device. On D-3 the P4 device was removed, two doses of prostaglandin F2α were administered concurrently and a patch was applied to evaluate expression of estrus. Artificial insemination was performed 72 h after P4 device removal (D0) simultaneously with the administration of 100 µg of gonadorelin acetate (GnRH-2). Increasing GnRH dose at initiation of a 5-day CO-Synch + P4 did not enhance ovulatory response (P = 0.57) to GnRH-1, expression of estrus (P = 0.79), nor pregnancies per AI (P/AI; P = 0.91). Both follicle size (quadratic) and circulating P4 (linear) affected (P < 0.01) ovulatory response to GnRH-1 independent of dose. Cows that had ovulation to GnRH-1 had smaller (P < 0.001) follicle size on D-3 and reduced (P = 0.05) expression of estrus compared to cows that did not have ovulation to GnRH-1, however, P/AI did not differ (P = 0.75). In conclusion, increasing the dose of GnRH-1 in the 5-day CO-Synch + P4 protocol did not enhance ovulatory response, expression of estrus, or P/AI in suckled beef cows.

Application of PGF2α at the moment of fixed-time artificial insemination in crossbred beef cows

Although studies have shown positive effects of gonadotropin releasing hormone (GnRH) or prostaglandin F_2α (PGF_2α) at the moment of fixed-time artificial insemination (FTAI) in the conception rate (CR) of cattle, its effects on treatments based on progesterone (P4) and estradiol benzoate (EB) is still not conclusive. The objective of this study was (1) to evaluate the effect of a PGF_2α analogue at FTAI in the CR of crossbred beef cows submitted to a 11d FTAI protocol based on P4 and EB; and (2) to describe the CR between PGF_2α-treated and control cows in different body condition scores (BCS) and parity categories. Crossbred (½ Nellore and ½ Angus) beef cows were submitted to a synchronization protocol and randomly assigned into 2 groups: Control (n = 163), at FTAI cows received 2 mL of saline solution as a placebo, and PGF_2α (n = 163), at FTAI cows were treated with PGF_2α analogue (10 mg of dinoprost tromethamine). Pregnancy diagnosis was performed 33d post-FTAI. Binary logistic regression model was used to analyze the effect of PGF_2α treatment on CR. There was no difference in CR between PGF_2α and control groups (P > 0.05; odds ratio (OR) = 0.92; confidence interval (CI) = 0.59-1.4). A greater CR was found in heifers (P = 0.0006, OR = 2.65, CI = 1.61 - 4.38) and multiparous (P = 0.0006, OR = 2.12, CI = 1.04 - 4.3) when compared to primiparous cows. Cows with low BCS (4; 9-point scale) showed lower CR when compared with moderate BCS (5-6; 9-point scale) (P < 0.05; OR = 0.10; CI = 0.06 - 0.18). There was no numerical difference on CR between PGF_2α-treated and control cows in different BCS and parity categories. The results suggested that the CR in this study was not influenced by 10 mg PGF_2α analogue at FTAI.

Comparison of two intravaginal progesterone-releasing devices in shortened-timed artificial insemination protocols in beef cattle

Commercially available intravaginal progesterone (P4) devices differ in shape, surface area and P4 load, which may affect the resulting pregnancy per AI (P/AI) following timed-AI (TAI). The objective of this study was to compare two intravaginal P4 devices on estrus rate, follicular dynamics and P/AI in beef cattle subjected to shortened-TAI protocols. In Expt. 1, nulliparous heifers were randomly assigned to a P4-releasing intravaginal device (PRID-Delta, 1.55 g P4) or a controlled internal drug release (CIDR, 1.38 g P4) at the initiation of a J-synch protocol. Heifers that displayed estrus 72 h following device removal were TAI, or if not in estrus given GnRH at 72 h and TAI at 90 h. In Expt. 2, nulliparous heifers and non-suckling cows were randomly assigned to either PRID or CIDR groups and either 1 or 2 mg of estradiol benzoate (EB) at initiation of a J-synch protocol. All cattle were TAI concurrent with GnRH 72 h after device removal. In Expt. 3, nulliparous heifers and suckling cows were randomly assigned to either PRID or CIDR groups and initiated a 5-d Cosynch protocol, with TAI concurrent with GnRH 72 h following device removal. In each experiment, cattle received estrus detection patches at device removal, which were then scored from 0 to 3 based on color change between initial application and TAI; 0 = unchanged, 1 = ≤50% change, 2 = >50% change, 3 = missing. Estrus was defined to have occurred when the patch was scored 2 or 3. Transrectal ultrasonography was used to determine cyclicity, diagnose pregnancy in all experiments, and the size of the ovulatory follicle in Expt. 3. In Expt. 1, the estrus rate was greater (72.0% vs. 61.0%; P = 0.04) in the PRID compared to the CIDR group. In Expt. 2, a parity by EB dose interaction (P = 0.02) was attributed to an increased estrus rate (52.8% vs. 41.4%; P = 0.05) in heifers given 1 vs. 2 mg EB. In Expt. 3, there was no difference in the ovulatory follicle diameter at device removal (P = 0.22) or TAI (P = 0.28) between P4 groups. Treatment with a PRID tended (P = 0.10) to increase the P/AI in cows compared to a CIDR (73.5% vs. 61.0%). In all experiments combined, the overall P/AI tended to increase (55.2% vs. 51.0%; P = 0.08) and P/AI in cattle exhibiting estrus increased (64.4% vs. 59.7%; P = 0.02) in cattle given a PRID compared to those given a CIDR, respectively. In summary, the type of intravaginal P4 device affected estrus response and P/AI following TAI in beef cows.

Effects on Synchronization and Reproductive Efficiency of Delaying the Removal of the Intravaginal Progesterone Device by 24 h in the 5d Co-Synch Protocol in Heifers

Simple Summary

Reproductive biotechnologies in beef farms are key issues, such as artificial insemination, fixed-time artificial insemination (FTAI), embryo transfer, and ovum pick up, among others. Artificial insemination takes the first place with these available tools. Thus, science keeps improving hormonal treatments and procedures to optimize pregnancies after insemination. A synchronization protocol commonly used in beef heifers is the 5d Co-synch protocol, which fits better in terms of ovarian synchronization and resulting conception rate. We propose a modification of this protocol, which consists of delaying by 24 h the removal of the intravaginal progesterone device, to decrease the percentage of heifers showing estrus before the date of FTAI. Moreover, this modification will make easier the workload when inseminating herds with heifers and cows at the same time. Based on our results, the protocol 5d Co-synch with the delayed removal of the intravaginal progesterone device fits as well as the original protocol in terms of synchronization and conception rate. Therefore, it can be implemented in the heifers of beef cattle commercial farms.

Abstract

In beef herds, increasing animal welfare, improving reproductive performance and easing animal management are key goals in farm economics. We explored whether delaying the removal of the intravaginal progesterone device by 24 h in heifers synchronized with a 5d Co-synch 72-h protocol could improve reproductive efficiency of fixed-time artificial insemination (FTAI). In experiment 1, we examined the total synchronization rate (TSR) in cycling Holstein heifers. Heifers (13.4 ± 0.69 mo.) were randomly assigned to the standard 5d Co-synch 56-h protocol (5dCo56; n = 10), 5d Co-synch 72-h (5dCo72; n = 17), or the modified 5d Co-synch 72-h protocol, in which removal of the progesterone device was delayed by 24 h (6dCo48; n = 19). In experiment 2, 309 cycling beef heifers on 18 commercial farms were subjected to the 5d Co-synch 72-h or 6-d Co-synch 48-h protocol and conception rate (CR) studied. In experiment 1, the three protocols led no differences on TSRs of 80.0% (5dCo56), 88.2% (5dCo72), and 89.5% (6dCo48). In experiment 2, the CR from the beef heifers, observed during two consecutive reproductive seasons did not differ: 59.7% for 5dCo72 and 62.0% for 6dCo48 (p = 0.907). Therefore, delaying removal by 24 h provides satisfactory results without reducing reproductive efficiency of heifers.

Estradiol cypionate administered at the end of a progesterone-based protocol for FTAI induces ovulation and improves postovulatory luteal function and uterine environment in anestrous beef cows

The objective of this study was to evaluate the effect of the administration of estradiol cypionate (ECP) at the end of an estradiol and progesterone-based protocol for fixed time artificial insemination (FTAI) on ovarian response and uterine function in postpartum anestrous beef cows. Multiparous suckled cows were randomly assigned to receive ECP at doses of 0 (control, n = 15), 0.5 (n = 15) or 1.0 mg (n = 15) im at the time of progesterone intravaginal insert removal. Serum 17β-estradiol concentrations at 24 h after insert removal were greater (P < 0.05) in both ECP treatments than in controls. No differences in estradiol were found between 0.5 mg and control cows (P > 0.1) from 48 h after insert removal until ovulation, although greater (P < 0.05) concentrations were maintained until ovulation in 1.0 mg ECP treated cows. Maximum 17β-estradiol concentration attained in each female was greater as ECP dose was greater (10.4 ± 0.4, 11.8 ± 0.5 and 13.5 ± 0.7, for control, 0.5 and 1.0 mg ECP treated cows, respectively; P < 005). Proportion of cows that ovulated tended to be greater (P = 0.06) in ECP treated than in control cows. Ovulation occurred earlier and the size of the ovulatory follicle was smaller (P < 0.05) for 1.0 mg but not for 0.5 mg (P > 0.1) when compared with control cows. After ovulation (Day 13 and 14), serum progesterone concentrations were greater (P < 0.05) in 0.5 and 1.0 mg ECP than control cows. Uterine environment on Day 6 after ovulation was affected by treatment; transcript expression of three of nine evaluated genes (i.e., estrogen, IGF-1 and insulin receptors genes) were upregulated (P < 0.05) after ECP treatment. In conclusion, ECP administration at progesterone insert removal in anestrous cows i) induces greater serum estradiol concentrations and tended to induce greater ovulation rate, ii) acts in a dose-dependent manner, as ECP dose increases ovulation occurs earlier and the size of the ovulatory follicle is smaller, iii) improves postovulatory luteal function and affects uterine gene expression. Altogether, this information contributes with the understanding of the effect of preovulatory estradiol exposure on ovulation and postovulatory ovarian and uterine function in anestrous beef cows.

Effect of equine chorionic gonadotropin (eCG) administration and proestrus length on ovarian response, uterine functionality and pregnancy rate in beef heifers inseminated at a fixed-time

The objective of the present study was to evaluate the effect of equine chorionic gonadotropin (eCG) administration associated to different proestrus lengths for Fixed-time AI (FTAI) in beef heifers. In Experiment 1, pre-pubertal heifers (n = 46) received a 6-day estradiol/progesterone-based treatment (J-Synch protocol), and were then allocated into four experimental groups in a 2 × 2 factorial design, to receive or not receive eCG (300 IU) at the time of intravaginal progesterone device removal, and to receive GnRH at 48 h or 72 h after device removal (to induce shortened and prolonged proestrus length, respectively). Endometrial samples were obtained 6 d after ovulation from the cranial portion of the uterine horn. The eCG administration induced greater serum estradiol-17β concentrations before ovulation (P < 0.05) and greater proportion of heifers bearing a competent corpus luteum after ovulation (P = 0.054). Delaying GnRH administration from 48 h to 72 h induced a longer interval from device removal to ovulation (i.e., prolonged proestrus; P < 0.05), larger diameter of the ovulatory follicle, and greater progesterone concentrations on Day 10-11 after ovulation. Heifers in eCG + GnRH72h group had more uterine receptors in luminal epithelium than those in eCG + GnRH48h group (PR and ERα), and than those in No eCG + GnRH72h group (PR) (P < 0.05). No effect of eCG or GnRH treatments was found in endometrial gene expression of progesterone and estrogen receptors. In Experiment 2, a total of 2,598 heifers received the J-Synch protocol associated or not with eCG administration at device removal, followed by FTAI/GnRH at 60 or 72 h after device removal (i.e., prolonged proestrus protocol). Heifers that received eCG had greater P/AI than those not receiving eCG (P < 0.05) and there was an interaction between eCG treatment and time of FTAI. The lowest P/AI was found in those heifers that received FTAI/GnRH at 72 h without eCG treatment at device removal (P < 0.05), and no differences were found between the other experimental groups. In conclusion, prolonging the length of proestrus in J-Synch protocol improves ovulatory follicular diameter and luteal function; and the administration of eCG at device removal improves preovulatory estradiol concentrations and luteal function. Finally, P/AI was enhanced by eCG treatment and the improvement was more evident when FTAI/GnRH was performed at 72 h after device removal.

Pregnancy rates to fixed-time AI in Bos indicus-influenced beef cows using PGF2α with (Bee Synch I) or without (Bee Synch II) GnRH at the onset of the 5-day CO-Synch + CIDR protocol

Objectives were to 1) characterize fixed-time AI (FTAI) pregnancy rates using the 5-Day CO-Synch + CIDR protocol in mature, suckled Bos indicus-influenced beef cows, 2) compare FTAI pregnancy rates in the latter to a modified version (5-Day Bee Synch + CIDR; Bee Synch I) that included treatment with prostaglandin F2α (PGF2α) at CIDR insertion on Day 0, and 3) test the hypothesis that elimination of both GnRH-1 at the onset of synchronization and the double dose of PGF on Day 5 (Bee Synch II) would not reduce FTAI pregnancy rates compared to Bee Synch I. For Experiment 1-trial 1, Brahman x Hereford (F-1) cows (n = 168) at least 40 d postpartum (PP; r = 40-92 d) at the time of CIDR insertion were administered the 5-Day CO-Synch + CIDR protocol with FTAI at 72 h after CIDR removal. Pregnancy rates to FTAI averaged 34.9 ± 1.9%. In Experiment 1-trial 2, fall- and spring-breeding Brahman x Hereford (F-1) beef cows (n = 269) were stratified by days PP and assigned randomly to receive either the 5-Day CO-Synch + CIDR (n = 136) or Bee Synch I (n = 133) protocol, with FTAI at 66 h after CIDR removal. Pregnancy rate to FTAI was greater (P < 0.05) in Bee Synch I (52.6 ± 0.9%) than in the 5-Day CO-Synch + CIDR procedure (40.4 ± 5.7%). For Experiment 2, 422 mature Braford, Brangus, Nelore x Brahman, and Brahman crossbred cows (Bos indicus proportion unknown) at 4 locations were treated with Bee Synch I, with FTAI at 66 h. Overall FTAI pregnancy rate averaged 51.7 ± 2.1%. Finally, from 2013 through spring 2018, we used a switchback design using fall- and spring-breeding herds to compare Bee Synch I (402 observations) to Bee Synch II (393 observations). Overall frequency of detected estrus at 66 h using ESTROTECT™ breeding indicator patches was 57.2 ± 2.4%, conception rates of those detected in estrus was 64.4 ± 3.5%, and FTAI pregnancy rates averaged 52.3 ± 2.4%, none of which differed between treatments. Moreover, pregnancy rates to FTAI in both treatments did not differ in cows synchronized between 40 and 80 d PP but increased after 80 d PP (P < 0.05). Bee Synch II, which eliminates GnRH-1 and the double dose of PGF2α on Day 5, results in FTAI pregnancy rates essentially identical to Bee Synch I but reduces synchronization costs and avoids the need for off-label (double dose PGF2α) drug use.

Comparison of the effects of two shortened timed-AI protocols on pregnancy per AI in beef cattle

The objective was to compare pregnancy per AI (P/AI) between two shortened timed-AI (TAI) protocols in beef cattle. This study also determined whether administration of eCG in heifers and timing of AI in cows would affect P/AI. Cattle were submitted at random to either a modified 5-d Co-synch protocol (Day 0 = progesterone releasing device (CIDR); Day 5 = CIDR removal and 500 μg of cloprostenol (PGF); Day 8 = 100 μg GnRH concurrent with AI) or J-synch protocol (Day 0 = CIDR insertion and 2 mg of estradiol benzoate i.m.; Day 6 = CIDR removal and 500 μg PGF; Day 9 = 100 μg GnRH concurrent with AI). In Experiment 1, 1135 heifers (13-15 mo of age) received an estrus detection patch (Estrotect™) on Day 5 and 579 were selected at random to receive 300 IU of equine chorionic gonadotropin (eCG) at the time of CIDR removal. Patches were scored from 0 to 3 based on color change between initial application and AI; 0 = unchanged, 1 = ≤ 50% change, 2 = > 50% change, 3 = missing. Estrus was defined to have occurred when the patch was scored 2 or 3. In Experiment 2, 399 cyclic, non-lactating beef cows from 1 location were submitted to either the modified 5-d Co-synch or J-synch protocol and within each protocol cows were TAI at either 66 ± 1 (n = 199) or 72 ± 1 h (n = 200) following CIDR removal. Transrectal ultrasonography was used in both experiments to determine presence of a corpus luteum (CL) on Day 0, and to diagnose pregnancy 35 d after TAI. In Experiment 1, eCG increased estrus rate only in heifers without a CL on day 0 that were submitted to the modified 5-d Co-synch protocol (41.9 vs. 69.6%). Heifers submitted to the J-synch protocol had greater (P = 0.03) P/AI compared with those in the modified 5-d Co-synch (48.7 vs. 41.1%) and heifers that expressed estrus before AI had increased (P < 0.0001) P/AI compared to those that did not (53.6 vs. 36.5%). Administration of eCG and presence of a CL tended to affect P/AI (P = 0.13). In Experiment 2, cows submitted to the J-synch protocol tended (P = 0.07) to have greater P/AI compared to those in the modified 5-d Co-synch (74.1 vs. 66.5%). There was no association between P/AI and timing of AI. In summary, the J-synch protocol resulted in greater P/AI than the modified 5-day Co-synch protocol in heifers and cows. Administration of eCG increased estrus rate in heifers without a CL at the start of the protocol and tended to improve P/AI in all heifers. Timing of AI (66 vs. 72 h) had no effect on P/AI in cows subjected to either TAI protocol.

Effect of induction of ovulation with estradiol benzoate at P4 device removal on ovulation rate and fertility in Bos indicus cows submitted to a TAI protocol

This study aimed to minimize the number of times cattle need to be confined during protocols for TAI in beef cows treated for induction of ovulation with EB at the time of P4 device removal (P4r). In Experiment 1, cows were treated with P4 plus EB (Day 0; AM) and were allocated to one of three groups at P4r: EB8.5, EB at P4r on Day 8.5 (PM; three confinements); EB9, EB 24 h after P4r on Day 8 (AM; four confinements) and EC8, EC at P4r on Day 8 (AM; positive control; three confinements). At P4r, cows were treated with PGF_2a plus eCG. Ultrasonography was performed from D8 to D12. The interval from P4r to ovulation was less in the EB8.5 compared to EB9 and EC8 group. There was no difference in the ovulation rate between groups. The variability of ovulation was greater in the EB8.5 and EC8 compared to EB9 group. In Experiment 2, cows of EC8 and EB9 groups were submitted to TAI 48 to 52 h (AM) or 54 to 58 h (PM) after P4r (D10). Cows of the EB8.5 group were submitted to TAI 38 to 42 h (AM) or 44 to 48 h (PM) after P4r (D10). There was no interaction between treatments and timing of AI and no treatment effect and timing of AI on P/AI. In conclusion, the delay compared to what typically occurs by 10 h of P4r concomitant with EB administration (Day 8.5) reduced the frequency of animal confinement for the TAI protocol without affecting the reproductive efficiency and the flexibility to perform the TAI in suckled beef cows.

Comparison between the 5-day cosynch and 7-day estradiol-based protocols for synchronization of ovulation and timed artificial insemination in suckled BOS taurus BEEF cows

The objective was to compare pregnancy per AI and follicular dynamic in suckled Bos taurus beef cows treated with either a 7-day progesterone + estradiol-based protocol or a 5-day progesterone CoSynch protocol for timed artificial insemination (TAI) during four breeding seasons. We hypothesized that estrous cycle status, days postpartum (DPP), fat depth and plasma progesterone concentration differentially modify the effect of treatments. Every year, 9 days before initiation of each breeding season, cows were randomly assigned to one of two groups. Cows in the 7-d P + E group (n = 428) received a progesterone intravaginal device (DIB) and estradiol benzoate on Day -9. On Day -2 the device was removed, and cows received cloprostenol and estradiol cypionate. Forty-eight hours later (Day 0) cows received TAI. Cows in the 5-d P + CoS group (n = 428) received a DIB, and GnRH on Day -8. On Day -3, the device was removed, and cows received cloprostenol. A second dose of cloprostenol was given on Day -2. Cows received GnRH and TAI 72 h after device removal (Day 0). On Day -9, estrous cycle status was determined. In a subset of cows (n = 79) the size of the dominant follicle was determined between Days -2 and 0. In another subset of cows (n = 340), DPP, fat depth (mm) and plasma progesterone concentration (ng/mL) were evaluated on Day -9. Pregnancy per AI was determined 30 d after TAI. Pregnancy per AI was greater for cows in the 5-d P + CoS group than for cows in the 7-d P + E group (50.9% vs. 41.3%, P = 0.01) and was also greater in cyclic than in anestrus cows (54.3% vs. 33.2%, P < 0.0001). There was also a significant effect of breeding season (P = 0.0002) and sire (P = 0.03), and an interaction between treatment group and breeding season (P = 0.03). The dominant follicle was larger (P < 0.0001) in cows in the 5-d P + CoS group than the 7-d P + E group (10.7 ± 0.29 mm vs. 9.0 ± 0.28 mm). Pregnancy per AI was greater in cows with ≥55 DPP (47.0% vs. 29.6%, P = 0.001), fat depth ≥0.50 mm (44.7% vs. 29.7%), and with plasma progesterone concentration ≥1 ng/mL (47.2% vs. 28.7%, P = 0.01). In cows with plasma progesterone ≥1 ng/mL on Day -9, pregnancy per AI was greater in the 5-d P + CoS group (60.5%) than in the 7-d P + E group (34.9%), but there was no difference between treatment groups in cows with plasma progesterone < 1 ng/mL (P = 0.07). In conclusion, the 5-d P + CoS protocol resulted in greater size of the dominant follicle and pregnancy per AI in suckled Bos taurus beef cows subjected to TAI.

Expression of estrus as a relevant factor in fixed-time embryo transfer programs using estradiol/progesterone-based protocols in cattle

The main objective of implementing embryo transfer in beef operations is to accelerate the rate of genetic progress in the herd. Among the main factors that affect the use of these technologies are related to nutrition, management and estrus synchronization. As a result of research conducted over the last 20 years, recipient utilization has increased by applying protocols that synchronize ovulation and allow for embryo transfer without the need for estrus detection, usually referred to as fixed-time embryo transfer (FTET). Although these protocols have performed adequately for several years, recent attention has been directed to the effect of estrus expression and estradiol concentrations during growth of the preovulatory follicle on embryo growth and pregnancy. The experiments reviewed herein demonstrate that estrus expression is associated positively with high pregnancy rates and reduced pregnancy losses in recipients receiving in vitro-produced and in vivo -derived frozen/thawed bovine embryos.

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.

Hormonal profile and follicular dynamics concurrent with CIDR and insulin modified Ovsync TAI programs and their impacts on the fertility response in buffaloes

Fifty one cyclic Egyptian buffaloes were used to study the hormonal profile and follicular dynamics concurrent with CIDR and insulin modified Ovsync TAI programs and their impacts on the consequent fertility responses. The buffaloes were randomly assigned into 3 ovulation synchronization protocols: Ovsync-alone (n = 13, control) CIDR-sync (n = 20) and Insulin-sync (n = 18). Ovsync-alone protocol consisted of two im injections of 20 μg bueserlin (GnRHa) on Day 0 (GnRH 1) and on Day 9 (GnRH 2) with an im injection of 500 μg of cloprostenol sodium (PGF₂ α) on Day 7. The CIDR-sync protocol consisted of the same treatment protocol as in Ovsync in addition to intra-vaginal insertion of CIDR (contains 1.38 gm of progesterone) on Day 0 followed by removal on Day 7. The Insulin-sync protocol consisted of the same treatment protocol as in Ovsync plus 3 sc injections of insulin at a dose of 0.25 i.u/1 kg, on Days 7, 8, and 9. Buffaloes in all groups were inseminated 16 h after GnRH2 by the same inseminator using frozen semen in straws. Blood samples were collected on Days 0, 3, 5 for serum progesterone assay and on Day 9 to measure serum concentrations of estradiol, insulin and IGF-1. Transrectal ultrasonographic scanning of the ovaries was conducted on Days 7, 8 and 9 to record the diameter of the largest follicle. Pregnancy diagnosis was conducted on Day 30 post-TAI by trans-rectal ultrasonographic scanning of the uterus to calculate conception rate. The serum progesterone concentration showed an increase (p < 0.01) in pregnant compared with non-pregnant buffaloes in both Ovsync-alone and Insulin-sync groups, but not in CIDR-sync group (p > 0.05) on Days 3 and 5. The serum estradiol concentration on Day 9 showed an increase (p < 0.01) in pregnant compared with the non-pregnant buffaloes in all of the treated groups. In Insulin-sync and Ovsync-alone groups, the diameter of the largest follicle (LF) was larger (p < 0.01) in pregnant compared with non-pregnant buffaloes, but in CIDR-sync, the diameter of the (LF) was larger (p < 0.01) in non-pregnant compared with pregnant buffaloes. Also, the results showed that the greatest diameter of LF was observed in pregnant buffaloes in Insulin-sync compared with either pregnant or non-pregnant buffaloes in all groups. It is concluded that modified CIDR-sync and Insulin-sync could improve fertility response through modulating hormonal profile and follicular dynamics in buffaloes during low breeding season.

Gestational dietary protein is associated with sex specific decrease in blood flow, fetal heart growth and post-natal blood pressure of progeny

STUDY OVERVIEW

The incidence of adverse pregnancy outcomes is higher in pregnancies where the fetus is male. Sex specific differences in feto-placental perfusion indices identified by Doppler assessment have recently been associated with placental insufficiency and fetal growth restriction. This study aims to investigate sex specific differences in placental perfusion and to correlate these changes with fetal growth. It represents the largest comprehensive study under field conditions of uterine hemodynamics in a monotocous species, with a similar long gestation period to the human. Primiparous 14 mo heifers in Australia (n=360) and UK (n=180) were either individually or group fed, respectively, diets with differing protein content (18, 14, 10 or 7% crude protein (CP)) from 60 d prior to 98 days post conception (dpc). Fetuses and placentae were excised at 98 dpc (n = 48). Fetal development an median uterine artery blood flow were assessed monthly from 36 dpc until term using B-mode and Doppler ultrasonography. MUA blood flow to the male feto-placental unit increased in early pregnancy associated with increased fetal growth. Protein restriction before and shortly after conception (-60 d up to 23 dpc) increased MUA diameter and indices of velocity during late pregnancy, reduced fetal heart weight in the female fetus and increased heart rate at birth, but decreased systolic blood pressure at six months of age.

CONCLUSION AND SIGNIFICANCE

Sex specific differences both in feto-placental Doppler perfusion indices and response of these indices to dietary perturbations were observed. Further, maternal diet affected development of fetal cardiovascular system associated with altered fetal haemodynamics in utero, with such effects having a sex bias. The results from this study provide further insight into the gender specific circulatory differences present in the fetal period and developing cardiovascular system.