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.

Ovarian response to prostaglandin F2α in lactating dairy cows: a clinical update

Prostaglandin F_2α (PGF_2α) and its analogs are used to induce luteolysis in estrus synchronization programs to terminate unwanted pregnancies or to promote ovulation in certain cow subpopulations. In the past few decades, the luteolytic dose of PGF_2α has remained unchanged. This review explores the clinical implications of increasing the standard dose for these applications in high-producing dairy cows. Ultrasonography may assist in selecting the most appropriate PGF_2α dose and improve the results. A reference has been used for PGF_2α for promoting ovulation in herds showing poor reproductive performance.

Effect of ovulation synchronization program and season on pregnancy to timed artificial insemination in suckled beef cows

This study was conducted to (i) evaluate the requirement for the administration of GnRH coincident with insertion of a progesterone-releasing intravaginal device (PRID) and (ii) the effect of supplementing with 400 IU eCG at PRID removal on pregnancy per AI (P/AI) in spring and autumn calving suckled beef cows, subjected to a 7-d CO-Synch + PRID timed artificial insemination (TAI) program. Suckled beef cows (n = 1408) on 62 commercial farms were enrolled and randomly assigned to either of three treatments: 1) cows received a PRID and 100 μg GnRH on Day -10, followed by 25 mg PGF_2α at PRID removal (Day -3) and 100 μg GnRH 72 h later (Day 0) at TAI (Treatment 1; n: spring = 236, autumn = 248); 2) as Treatment 1, but without GnRH at PRID insertion on Day -10 (Treatment 2; n: spring = 232, autumn = 227); 3) as Treatment 1, but cows also received 400 IU eCG at PRID removal on Day -3 (Treatment 3; n: spring = 233, autumn = 232). At Day -10, ovaries were examined by ultrasonography to evaluate the presence or absence of a corpus luteum (CL) and follicle(s) ≥ 10 mm in diameter. Body condition score (BCS) was assessed on a scale of 1-5. Pregnancy diagnosis was carried out 30-35 d after TAI by transrectal ultrasonography. Data were analyzed using the GENMOD and LOGISTIC procedures of SAS. There was a treatment by season interaction for P/AI (P < 0.001). In spring, overall P/AI was 59.1% (414/701) and was affected by treatment (59.3 v 49.6 v 68.2%, for Treatments 1, 2 and 3, respectively P < 0.05). In contrast, in autumn, overall P/AI (51.5%, 364/707) was unaffected (P > 0.05) by treatment (50.1 v 53.7 v 48.7% for Treatments 1, 2 and 3, respectively). Overall, eCG had a positive effect on P/AI for cows lacking a CL at treatment initiation (P < 0.05). In addition, in cows with low BCS (≤2.25), eCG supplementation tended (P = 0.09) to improve P/AI. Seasonal differences in response to synchronization treatment may be reflective of different management regimens (grazing v confinement) and breed type and remain to be elucidated.

Presence of multiple corpora lutea affects the luteolytic response to prostaglandin F2α in lactating dairy cows

Since the 1970s, luteolytic doses used for synchronizing estrus in dairy cattle have remained unchanged. This study aimed to evaluate the dose-response effect of prostaglandin F_2α (PGF_2α), which is used for synchronizing estrus, and subsequent fertility in cows with two or more corpora lutea (CL). The study population consisted of 1,683 cows with a single CL (1CL), 501 cows with multiple CL receiving a single dose of PGF_2α (2CL1), and 252 cows with multiple CL receiving a 1.5 × PGF_2α dose (2CL1.5). Cows with a single CL (n = 1,245) showed estrus significantly (P < 0.01) earlier (3.01 ± 1.23 days; mean ± SD) than cows with multiple CL (n = 287; 3.33 ± 1.69 days). Using 1CL cows as reference, the odds ratio (OR) for the estrus response in 2CL1 cows was 0.13 (P < 0.0001), whereas the ORs for estrus response and pregnancy of 2CL1.5 cows were 1.8 (P = 0.0001) and 1.7 (P = 0.001), respectively. Based on the results for only the 2CL1 cows, the OR for the estrus response was 0.7 (P = 0.01) for cows producing ≥ 45 kg of milk at treatment, compared to the remaining cows producing < 45 kg of milk. Our results showed that the presence of multiple CL reduced the estrus response to that induced by a single PGF_2α dose and milk production was inversely associated with this response, whereas an increased PGF_2α dose improved the estrus response. Therefore, an increase in the standard PGF_2α dose is recommended.

Clinical prospects proposing an increase in the luteolytic dose of prostaglandin F2α in dairy cattle

Over the past few decades, the luteolytic dose of prostaglandin F_2α (PGF_2α) and its analogs, used to synchronize estrus for fixed-time insemination in dairy cattle, have remained unchanged. Given the beneficial effects of PGF_2α on a young corpus luteum and on multiple ovulations in a fixed-time insemination protocol, and its therapeutic abortive effects on multiple ovulations in pregnant cows, we propose the use of a double PGF_2α dose or two PGF_2α treatments 24 hours apart. Ultrasonography procedures serve to identify luteal structures and may therefore help to determine the best PGF_2α dose to improve the fertility of high-producing dairy cows.

Synchronization and resynchronization strategies to improve fertility in dairy buffaloes

Dairy buffalo has an integral role in the sustenance of economics due to its substantial contribution in milk and meat industry, however, the reproduction in this species is challenging. During the last decade, our laboratory conducted a series of experiments to encapsulate the solutions of the problems through optimizing pre- and post-insemination interventions in dairy buffaloes. In an unique study, we proposed that timing of ovulation with reference to the onset of standing heat during spontaneous estrus is delayed, and subsequently re-framed the traditional AM-PM rule (AI after 12 h of standing heat) to AM-AM or PM-PM (AI after 24 h of standing heat) to achieve the optimum fertility using frozen thawed semen in dairy buffaloes. Pregnancy per AI (P/AI) varied substantially either via injecting single shot of prostaglandin (PG) F_2α to perform AI at detected estrus or applying standard ovsynch protocol for timed AI (TAI) in buffaloes. However, estrus response, and P/AI remained similar either with used or new controlled internal drug release device in dairy buffaloes. Additionally, the incorporation of estradiol benzoate in progesterone (P4) based protocol resulted in controlled emergence of follicular wave and increased the estrus intensity in buffaloes. Thereafter, we fine-tuned P4-based protocols to optimize the ovulation window for TAI either using GnRH or human chorionic gonadotropin (hCG) or equine chorionic gonadotropin that ultimately improved the fertility in dairy buffaloes. Although, these hormonal interventions resulted in decent fertility, yet it was consistently being compromised due to early or late embryonic losses in dairy buffaloes. Administration of hCG or GnRH on d 7 or 23 or 25 post AI has been proved beneficial to enhance the embryonic survival in buffaloes. Recently, resynchronization program as an aggressive reproductive management approach has been tested that served as a dual-purpose tool to increase overall herd fertility and reduce embryonic losses at commercial buffalo farm operations. Taken together, we concluded that the solutions to the problems of reproductive function are now clearly available with acceptable fertility, however, their application to the small holder buffalo farming remains challenging.

Effects of prostaglandin F2α (PGF2α) on cell-death pathways in the bovine corpus luteum (CL)

BACKGROUND

Prostaglandin F_2α (PGF_2α) may differentially affect viability of luteal cells by inducing either proliferation or cell death (via apoptosis or necroptosis). The diverse effects of PGF_2α may depend on its local vs. systemic actions. In our study, we determined changes in expression of genes related to: (i) apoptosis: caspase (CASP) 3, CASP8, BCL2 associated X (BAX), B-cell lymphoma 2 (BCL2) and (ii) necroptosis: receptor-interacting protein kinase (RIPK) 1, RIPK3, cylindromatosis (CYLD), and mixed lineage kinase domain-like (MLKL) in the early and mid-stage corpus luteum (CL) that accompany local (intra-CL) vs. systemic (i.m.) analogue of PGF_2α (aPGF_2α) actions. Cows at day 4 (n = 24) or day 10 (n = 24) of the estrous cycle were treated by injections as follows: (1) systemic saline, (2) systemic aPGF_2α (25 mg; Dinoprost), (3) local saline, (4) local aPGF_2α (2.5 mg; Dinoprost). After 4 h, CLs were collected by ovariectomy. Expression levels of mRNA and protein were investigated by RT-q PCR, Western blotting and immunohistochemistry, respectively.

RESULTS

We found that local and systemic administration of aPGF_2α in the early-stage CL resulted in decreased expression of CASP3 (P < 0.01), but CASP8 mRNA expression was up-regulated (P < 0.05). However, the expression of CASP3 was up-regulated after local aPGF_2α treatment in the middle-stage CL, whereas systemic aPGF_2α administration increased both CASP3 and CASP8 expression (P < 0.01). Moreover, we observed that both local and systemic aPGF_2α injections increased RIPK1, RIPK3 and MLKL expression in the middle-stage CL (P < 0.05) while CYLD expression was markedly higher after i.m. aPGF_2α injections (P < 0.001). Moreover, we investigated the localization of necroptotic factors (RIPK1, RIPK3, CYLD and MLKL) in bovine CL tissue after local and systemic aPGF_2α injections in the bovine CL.

CONCLUSION

Our results demonstrated for the first time that genes related to cell death pathways exhibit stage-specific responses to PGF_2α administration depending on its local or systemic actions. Locally-acting PGF_2α plays a luteoprotective role by inhibiting apoptosis and necroptosis in the early CL. Necroptosis is a potent mechanism responsible for structural CL regression during PGF_2α-induced luteolysis in cattle.

Short communication: Reproduction outcomes in dairy heifers following a 14-d progesterone insert presynchronization protocol

The objectives were to evaluate pregnancy per artificial insemination (AI), days to first AI, and proportion pregnant within 7 d of AI eligibility in dairy heifers subjected to presynchronization compared with dairy heifers not presynchronized. Thirty days before AI eligibility, Holstein heifers were assigned randomly to 1 of 3 groups: 14-d controlled internal drug release (CIDR; containing progesterone) presynchronization, PGF_2α presynchronization, or control (no presynchronization). Heifers in the 14-d CIDR presynchronization treatment (n = 119) received a CIDR on d -30, which was removed on d -16, followed by an injection of PGF_2α upon entry to the breeding program (d 0). Heifers in the PGF_2α presynchronization treatment (n = 118) received an injection of PGF_2α on d -11 and d 0. Control heifers (n = 121) were not presynchronized and received an injection of PGF_2α on d 0. All heifers received tail paint on d 0 to facilitate once-daily detection of estrus (based on paint removal). Heifers detected in estrus received AI with conventional semen on the same morning as detected estrus. Generalized linear mixed models were used to assess mean treatment differences. Following PGF_2α treatment on d 0, more heifers were detected in estrus in the first 7 d after eligibility in the 14-d CIDR group (95.8%) compared with the PGF_2α (74.6%) and control (66.9%) groups. Days to first AI differed between treatments (14-d CIDR = 3.6 d vs. PGF_2α = 5.0 d vs. control = 6.8 d). Pregnancy per AI for first AI within 7 d of eligibility was 71.9% (14-d CIDR), 58.0% (PGF_2α), and 61.7% (control), and differed between 14-d CIDR and PGF_2α heifers. Presynchronization with a 14-d CIDR increased the proportion of heifers pregnant in the first 7 d of eligibility (14-d CIDR = 68.9% vs. PGF_2α = 43.2% vs. control = 41.3%). Projected days on feed (d 0 to projected calving date) were 295 (14-d CIDR), 302 (PGF_2α), and 305 (control), and were different between the 14-d CIDR and control heifers. The potential economic benefit to the producer was $15.85 per heifer presynchronized with a 14-d CIDR protocol compared with the control group. Treatment of dairy heifers with a 14-d CIDR effectively presynchronized estrus, resulting in a greater proportion detected in estrus, reduced days to first AI, and an increased proportion of heifers pregnant within the first 7 d after breeding eligibility compared with heifers presynchronized with a single PGF_2α injection and control heifers.

A 100-Year Review: Practical female reproductive management

Basic knowledge of mechanisms controlling reproductive processes in mammals was limited in the early 20th century. Discoveries of physiologic processes and mechanisms made early in the last century laid the foundation to develop technologies and programs used today to manage and control reproduction in dairy cattle. Beyond advances made in understanding of gonadotropic support and control of ovarian and uterine functions in basic reproductive biology, advancements made in artificial insemination (AI) and genetics facilitated rapid genetic progress of economically important traits in dairy cattle. Technologies associated with management have each contributed to the evolution of reproductive management, including (1) hormones to induce estrus and ovulation to facilitate AI programs; (2) pregnancy diagnosis via ultrasonography or by measuring conceptus-derived pregnancy-associated glycoproteins; (3) estrus-detection aids first devised for monitoring only physical activity but that now also quantitate feeding, resting, and rumination times, and ear temperature; (4) sex-sorted semen; (5) computers and computerized record software packages; (6) handheld devices for tracking cow location and retrieving cow records; and (7) genomics for increasing genetic progress of reproductive and other economically important traits. Because of genetic progress in milk yield and component traits, the dairy population in the United States has been stable since the mid 1990s, with approximately 9 to 9.5 million cows. Therefore, many of these technologies and changes in management have been developed in the face of increasing herd size (4-fold since 1990), and changes from pastoral or dry-lot dairies to increased housing of cows in confinement buildings with freestalls and feed-line lockups. Management of groups of "like" cows has become equally important as management of the one. Management teams, including owner-managers, herdsmen, AI representatives, milkers, and numerous consultants dealing with health, feeding, and facilities, became essential to develop working protocols, monitor training and day-to-day chores, and evaluate current trends and revenues. Good management teams inspect and follow through with what is routinely expected of workers. As herd size will undoubtedly increase in the future, practical reproductive management must evolve to adapt to the new technologies that may find more herds being milked robotically and applying technologies not yet conceived or introduced.

Reproduction in domestic ruminants during the past 50 yr: discovery to application

The study of reproductive physiology in domestic ruminants has progressed from the whole animal to the molecular level in an amazingly short period of time. The volume of information on this subject is enormous; therefore, we have focused on domestic ruminants, with an emphasis on cattle. To date, artificial insemination (AI) is perhaps the most powerful technique that reproductive physiologists and geneticists have provided the livestock industry for genetic improvement. Early efforts to establish AI as a tool were initiated in Russia around 1899 and since that time major advances in methods of semen collection, evaluation of male fertility, cryopreservation of sperm, sex-sorted semen, and estrous cycle control have occurred. The preceding advances not only led to the widespread use of AI, but also contributed to our fundamental understanding of ovulation control, timing of insemination, gamete biology, and cryopreservation. In regards to anestrus, our understanding of the concept of neuroendocrine control of the pituitary gland and the role of steroid feedback led to the Gonadostat Theory, which proposes that onset of puberty is due to a decrease in the negative feedback of gonadal steroids over time. Subsequent studies in prepuberal and postpartum sheep and cattle established that a short luteal phase frequently precedes the first normal length cycle that is accompanied by estrous expression. This observation led to the common practice of treating prepuberal heifers and anestrous postpartum cows with a short-term progestin treatment (e.g., Controlled Internal Drug Release) to induce normal estrous cycles. In domestic ruminants, fertilization rate is high (85% to 95%); however, significant embryonic mortality before or around the time of maternal recognition of pregnancy (MRP) reduces the pregnancy rate to a single breeding. Significant effort has been directed at determining the time of MRP, the signal for MRP, as well as elucidating the physiological, cellular, and molecular dialogue between the conceptus and uterine environment. Advancements have now led us to the ability to edit the genome to alleviate disease and possibly improve production traits. In summary, major advancements in our understanding of reproductive biology have stemmed from efforts to establish the AI and embryo transfer technique and reduce the negative impact of anestrus and embryonic mortality in domestic ruminants.

Synthesis of Alfaprostol and PGF2α through 1,4-Addition of an Alkyne to an Enal Intermediate as the Key Step

The veterinary drug Alfaprostol and prostaglandin PGF_2α have been synthesized in just nine steps. The strategy involved the conjugate addition of an alkyne to a bicyclic enal, available in three steps by a proline-catalyzed aldol reaction of succinaldehyde. In the case of Alfaprostol, this resulted in the shortest synthesis reported to date. For PGF_2α, this approach improved our previous route by making the 1,4-addition and ozonolysis more operationally simple.

Additional small dose of prostaglandin F2α at timed artificial insemination failed to improve pregnancy risk of lactating dairy cows

Two experiments were performed to test the hypothesis that administering PGF_2α concurrent with timed artificial insemination (AI) in lactating dairy cows would enhance pregnancy per AI (P/AI). In experiment 1, lactating Holstein cows (n = 289) in one herd were enrolled after a non-pregnancy diagnosis (30-36 d after AI) to synchronize subsequent ovulation before AI. Cows were assigned randomly to receive (im) 10 mg of PGF_2α concurrent with timed AI (Day 0; treatment) or no injection (control). Blood samples were collected on Days -3, 0, and 13 to determine serum concentrations of progesterone. Ovaries were scanned via transrectal ultrasonography to determine follicle diameters (Day -3), subsequent ovulation risk (Day 13), and total volume of luteal tissue (Day 13). Diagnosis of pregnancy occurred on Days 32 and 80 after AI. Ovulation risk post-AI exceeded 90% and did not differ between treatments. In addition, PGF_2α treatment only numerically increased progesterone (5.7 ± 0.3 vs. 6.2 ± 0.3 ng/mL) or luteal tissue volume (8.9 ± 0.4 vs. 9.8 ± 0.5 ng/mL) on Day 13 by 8.8% (P = .206) or 10.1% (P = .134) in control and treated cows, respectively. Pregnancy per AI at Days 32 (P = .50) and 80 (P = .33) did not differ between treatments. Cows with progesterone >0.5 ng/mL at timed AI had reduced (P < .001) ovulation risk but risk was unaffected by treatment. In experiment 2, lactating dairy cows (n = 1828) in two commercial dairy herds were enrolled at time of insemination (Day 0), and assigned randomly to treatment or control as described in experiment 1. Initial (Days 32-35) and confirmed (Days 63-68) pregnancy diagnosis revealed no differences in P/AI or pregnancy loss. Pregnancy diagnosis on Days 32-35 produced percentage increases in P/AI for primiparous compared with multiparous cows (20.8%; P = .002), for first-service compared with repeat-service cows (26%; P = .001), and cows in one herd compared with the second herd (36%; P < .001). Pregnancy loss was greater (P = .001) for cows inseminated at first (10.0%) vs. later services (5.3%) but was unaffected by treatment. Cows treated with PGF_2α in one herd produced more twins than control cows (11.7 vs. 3.2%), whereas no treatment difference was detected in the second herd (5.6 vs. 5.6%), respectively. We conclude that im treatment of lactating dairy cows with 10 mg of PGF_2α concurrent with timed AI did not improve P/AI or embryo survival, but increased twinning in one herd.

Effect of different gonadorelin (GnRH) products used for the first or resynchronized timed artificial insemination on pregnancy rates in postpartum dairy cows

Different GnRH products are used for timed artificial insemination (AI) in postpartum dairy cows. Previous studies reported greater LH release and increased ovulation percentage for gonadorelin diacetate tetrahydrate compared with gonadorelin hydrochloride but pregnancies per AI (P/AI) were not evaluated. The objective, therefore, was to compare P/AI for cows treated with either gonadorelin hydrochloride or gonadorelin diacetate tetrahydrate before the first timed AI or resynchronized timed AI. Holstein cows (n = 3938) in a confinement dairy in northeast Missouri were assigned to weekly cohorts (n = 22) on the basis of calving date. Cows were treated with "Presynch Ovsynch" (PGF2α, 14 days; PGF2α, 14 days; GnRH, 7 days; PGF2α, 56 hours; GnRH, 16 hours; timed AI) so that the first timed AI was 70 to 76 days postpartum. The PGF2α was Lutalyse (5 mL; 25 mg; Zoetis). The GnRH product was either gonadorelin hydrochloride (2 mL; 100 μg; n = 1945) or gonadorelin diacetate tetrahydrate (2 mL; 100 μg; n = 1993) and alternated weekly for cows assigned to cohorts. There were first timed AI (n = 1790) and resynchronized timed AI (n = 2148) cows within each cohort. The resynchronization began 32 days after timed AI (GnRH, 6 days; ultrasound pregnancy diagnosis, 1 day; and then for nonpregnant cows: PGF2α, 56 hours; GnRH, 16 hours; timed AI). The trial was conducted from January to February 2012 (n = 1203) and July to October 2012 (n = 2735). Cows were fed a total mixed ration, milked thrice daily, and milk tested monthly for volume, somatic cell count (SCC), fat percentage, protein percentage, and milk urea nitrogen. Data were analyzed by fitting the binary response data to a generalized linear mixed model for repeated measures. There was no effect of the GnRH product (treatment) on P/AI (38.4 ± 1.2 vs. 35.7 ± 1.3; gonadorelin diacetate tetrahydrate vs. gonadorelin hydrochloride). Treatment interactions with parity, month of breeding, or insemination number were not significant. The first-service P/AI (38.8 ± 1.4%) was greater (P < 0.05) than the resynchronized P/AI (35.3 ± 1.3%). Cows inseminated in the summer had lesser P/AI (effect of month; P < 0.001) compared with cows inseminated in the winter. There was a decrease (P < 0.002) in timed AI conception for cows with a greater milk SCC and an increase (P < 0.003) in P/AI for cows with a greater milk protein percentage. In conclusion, the GnRH product did not affect P/AI for the first or resynchronized timed AI in an Ovsynch-based program. Other factors affected P/AI including service number (lesser for the second service or greater), month (lesser in summer months), SCC (lesser for cows with greater SCC), and milk protein percentage (greater for cows with greater protein percentage).

Impacts of reproductive technologies on beef production in the United States

Estimations of world population growth indicate that by the year 2050 we will reach nine billion habitants on earth. These estimates impose a tremendous challenge in the current agricultural systems as food supply will need to increase by 100 % in the next 40 years (Food and Agriculture Organization of the United Nations 2009). Beef will be a primary protein source that will assist in meeting the requirements for a portion of the protein in diets of this expanding global populace. Beef is a high-quality protein that contains all essential amino acids for the human body and also contains additional essential nutrients such as iron, zinc, B vitamins, riboflavin, selenium, choline, and conjugated linoleic acid (CLA). Adopting reproductive technologies at greater rates than currently used is a viable method to dramatically enhance production efficiency of beef cattle enterprises.Artificial insemination (AI), estrous synchronization and fixed-time AI (TAI), semen and embryo cryopreservation, multiple ovulation and embryo transfer (MOET), in vitro fertilization, sex determination of sperm or embryos, and nuclear transfer are technologies that are used to enhance the production efficiency of beef operations. In many cases, the development of these technologies is responsible for significant changes to traditional livestock production practices. However, adoption of these technologies appears to has not grown at the same rate in the United States as other formidable beef producing nations. For example, sales of beef semen for AI increased from 3.3 to 11.9 million units between 1993 and 2011 in Brazil, whereas that in the United States has increased from 2.9 to 3.8 million units during the same period. The significant increases in adoption of reproductive technologies in developing countries is likely as a result of the development of practical estrous synchronization and TAI systems that have allowed beef producers the opportunity to eliminate detection of estrus in their AI programs with a high degree of success. In the United States, slow adoption rates of these technologies may result in a future loss of international market share of beef products as other nations take advantage not only of the additional kilogram of beef that can be produced but also the improved quality of beef that can be realized through incorporation of reproductive technologies and resultant genetic improvement. However, current difficulties the US producers have with the incorporation of applied reproductive technologies, such as TAI, MOET, and sex semen, must not be the reason to overlook and incorporate more traditional reproductive technologies such as castration, breeding season management, or weaning. In many cases, beef producers in the United States fail to incorporate these more traditional technologies, which results in a reduction in production efficiency of the US beef industry. This chapter will focus on both traditional and more developed reproductive technologies that will play a role in enhancing future production efficiencies of the US beef cattle production system.

Luteal function, largest follicle, and fertility in postpartum dairy cows treated with 14dCIDR-PGF2α versus 2xPGF2α-Ovsynch for timed AI

A method for timed artificial insemination (AI) that is used for beef cows, beef heifers, and dairy heifers employs progesterone-releasing inserts, such as the controlled internal drug release (CIDR; Zoetis, New York, NY, USA) that are left in place for 14 days. The 14-day CIDR treatment is a method of presynchronization that ensures that cattle are in the late luteal phase of the estrous cycle when PGF2α is administered before timed AI. The objective of this study was to test the effectiveness of the 14dCIDR-PGF2α program in postpartum dairy cows by comparing it with the traditional "Presynch-Ovsynch" (2xPGF2α-Ovsynch) program. The 14dCIDR-PGF2α cows (n = 132) were treated with a CIDR insert on Day 0 for 14 days. At 19 days after CIDR removal (Day 33), the cows were treated with a luteolytic dose of PGF2α, 56 hours later were treated with an ovulatory dose of GnRH (Day 35), and 16 hours later were inseminated. The 2xPGF2α-Ovsynch cows were treated with a luteolytic dose of PGF2α on Day 0 and again on Day 14. At 12 days after the second PGF2α treatment (Day 26), the cows were treated with GnRH. At 7 days after GnRH, the cows were treated with PGF2α (Day 33), then 56 hours later treated with GnRH (Day 35), and then 16 hours later were inseminated. There was no effect of treatment or treatment by parity interaction on pregnancies per AI (P/AI) when pregnancy diagnosis was performed on Day 32 (115/263; 43.7%) or Days 60 to 90 (99/263; 37.6%) after insemination. There was an effect of parity (P < 0.05) on P/AI because primiparous cows had lesser P/AI (35/98; 35.7%) than multiparous cows (80/165; 48.5%) on Day 32. Cows observed in estrus after the presynchronization step (within 5 days after CIDR removal or within 5 days after the second PGF2α treatment) had greater P/AI than those not observed in estrus (55/103; 53.4% vs. 60/160; 37.5%; observed vs. not observed; P < 0.01; d 32 pregnancy diagnosis). When progesterone data were examined in a subset of cows (n = 208), 55.3% of cows had a "prototypical" response to treatment (i.e., the cow had an estrous cycle that was synchronized by the presynchronization treatment and then the cow responded appropriately to the subsequent PGF2α and GnRH treatments before timed AI). Collectively, cows with a prototypical response to either treatment had 52.2% P/AI that was greater (P < 0.001) than the P/AI for cows that had a nonprototypical response (19%) (P/AI determined at 60-90 days of pregnancy). In conclusion, we did not detect a difference in P/AI when postpartum dairy cows were treated with 14dCIDR-PGF2α or 2xPGF2α-Ovsynch before timed AI. The primary limitation to the success of either program was the failure of the cow to respond appropriately to the sequence of treatments.

Short communication: presynchronization for timed artificial insemination in grazing dairy cows by using progesterone for 14 days with or without prostaglandin F2α at the time of progesterone withdrawal

Progesterone-containing devices can be inserted intravaginally for 14 d to presynchronize the estrous cycle for timed artificial insemination (TAI) in beef heifers ("14-day CIDR-PG" or "Show-Me-Synch" program). The progesterone treatment is effective for presynchronization because cattle develop a persistent dominant follicle during treatment that ovulates within 3 d after progesterone removal. The subsequent estrous cycle can be effectively used for a TAI program. Some cattle will retain a functional corpus luteum (CL) for the entire 14-d treatment period and will not be synchronized effectively because the interval to ovulation depends on the lifespan of their existing CL. The objective was to test the effect of a luteolytic dose of PGF(2α) at progesterone removal for improving synchrony of estrus after treatment and increasing conception rate to a subsequent TAI in dairy cows. Postpartum cows (n = 1,021) from 2 grazing dairy herds were assigned to 1 of 2 presynchronization programs that used a controlled internal drug releasing (CIDR) device containing progesterone: 14dCIDR (CIDR in, 14 d, CIDR out; n = 523) or 14dCIDR+PGF(2α) (CIDR in, 14 d, CIDR out, and PGF(2α); n = 498). Cows were body condition scored (BCS; 1 to 5, thin to fat) and tail painted at CIDR removal. Paint score (PS) was recorded after CIDR removal [PS = 0 (all paint removed, indication of estrus), PS = 3 (paint partially removed), or PS = 5 (no paint removed; indication of no estrus)]. At 19 d after CIDR removal, all cows were treated with PGF(2α), 56 h later treated with GnRH, and then 16 h later were TAI. Treating cows with PGF(2α) at CIDR removal increased the percentage with PS = 0 within 5 d (58.1% vs. 68.9%; 14dCIDR vs. 14dCIDR+PGF(2α)). We found no effect of treatment, however, on conception rate at TAI (41.1% vs. 43.6%; respectively). The TAI conception rate increased with increasing BCS and was greater for cows that had PS = 0 within 5 d after CIDR removal. In summary, treating cows with PGF(2α) at CIDR removal increased the percentage of cows with all tail paint removed but did not increase percentage of pregnant cows after TAI.

Advances in modeling of the bovine estrous cycle: synchronization with PGF2α

Our model of the bovine estrous cycle is a set of ordinary differential equations which generates hormone profiles of successive estrous cycles with several follicular waves per cycle. It describes the growth and decay of the follicles and the corpus luteum, as well as the change of the key reproductive hormones, enzymes and processes over time. In this work we describe recent developments of this model towards the administration of prostaglandin F2α. We validate our model by showing that the simulations agree with observations from synchronization studies and with measured progesterone data after single dose administrations of synthetic prostaglandin F2α.

Physiology and Endocrinology Symposium: Harnessing basic knowledge of factors controlling puberty to improve synchronization of estrus and fertility in heifers

The development of replacement heifers is a major economic investment for all beef and dairy operations. The costs associated with heifer development cannot be recovered if heifers do not conceive and remain productive in the herd; therefore, heifers need to conceive early in the breeding season or risk being culled. Previous research has reported up to a 21% increase in fertility from pubertal estrus to the third estrus of a heifer. The use of reproductive tract scores to determine pubertal status has demonstrated that peripubertal and pubertal heifers have increased pregnancy success to estrous synchronization compared with heifers that were prepubertal. The development of RIA has allowed accurate measurement of peripheral blood hormone concentrations associated with the pubertal process and luteal formation. This basic knowledge has increased our understanding of the mechanisms that control puberty in heifers. In addition, understanding the hormonal changes that occur during the estrous cycle has allowed for the development of estrous synchronization protocols that result in increased control of follicular growth, regression of luteal tissue, and ovulation. Transrectal ultrasonography has increased our understanding of follicular waves; this understanding led to research investigating the endocrine regulation of follicular waves and development of methods to synchronize follicular waves for purposes of fixed-time AI. Current topics of research include the effect of antral follicle count on fertility and the effect of maternal nutrition (on the fetus in utero) on subsequent reproductive potential of a heifer (i.e., fetal programming). Advancements in genomic technologies will likely provide a powerful tool for selecting heifers at birth that will have a greater probability of being reproductively successful if managed correctly. Therefore, knowledge gained through basic research on factors that control puberty has improved and will continue to improve heifer development and fertility.

Influence of inducing luteal regression before a modified fixed-time artificial insemination protocol in postpartum beef cows on pregnancy success

Most fixed-time insemination protocols utilize an injection of GnRH at the beginning of the protocol to initiate a new follicular wave. However, the ability of GnRH to initiate a new follicular wave is dependent on the stage of the estrous cycle. We hypothesized that administering PGF(2α) 3 d before initiating a fixed-time AI protocol would improve synchrony of follicular waves and result in greater pregnancy success. Therefore, our objective was to determine whether inducing luteal regression 3 d before a fixed-time AI protocol would improve control of follicular turnover and pregnancy success to fixed-time AI. Multiparous crossbred cows at 3 locations (n = 108, 296, and 97) were randomly assigned to 1 of 2 treatments: 1) PGF(2α) [25 mg; intramuscularly (i.m.)] on d -9, GnRH (100 μg; i.m.) and insertion of a controlled internal drug-releasing device (CIDR) on d -6, PGF(2α) (25 mg; i.m.) and CIDR removal with PGF(2α) (25 mg; i.m.) at CIDR removal on d 0 (PG-CIDR) or 2) GnRH (100 μg; i.m.) and insertion of a CIDR on d -5 and CIDR removal with PGF(2α) (25 mg; i.m.) at CIDR removal and 4 to 6 h after CIDR removal (5-d CIDR). Cows were time-inseminated between 66 and 72 h (PG-CIDR) or 70 to 74 h (5-d CIDR) after CIDR removal, and GnRH was administered at the time of fixed-time AI. At location 1, ovulatory response to the first injection of GnRH was determined by ultrasonography at the time of GnRH and 48 h after GnRH administration. Among cows with follicles ≥10 mm in diameter, more (P = 0.03) PG-CIDR-treated cows ovulated after the initial GnRH injection (88%, 43/49) compared with the 5-d CIDR-treated cows (68%, 34/50). Pregnancy outcome was not influenced by location (P = 0.96), age of the animal (P = 1.0), cycling status (P = 0.99), BCS (P = 1.0), or any 2-way interactions (P ≥ 0.13). However, pregnancy success was influenced by synchronization protocol (P = 0.04). Pregnancy outcome was greater (P = 0.04) for the PG-CIDR protocol (64%) compared with the 5-d CIDR protocol (55%). In summary, control of follicular turnover was improved by inducing luteal regression 3 d before initiation of a fixed-time AI protocol, and pregnancy success was improved with the PG-CIDR protocol compared with the 5-d protocol.

Influence of inducing luteal regression before a modified controlled internal drug-releasing device treatment on control of follicular development

At the initiation of most controlled internal drug-releasing (CIDR) device protocols, GnRH has been used to induce ovulation and reset follicular waves; however, its ability to initiate a new follicular wave is variable and dependent on stage of the estrous cycle. The objectives of the current studies were to determine 1) if inducing luteal regression before the injection of GnRH at time of insertion of a CIDR resulted in increased control of follicular development, and 2) if removing endogenous progesterone by inducing luteal regression before insertion of the CIDR decreased variation in LH pulse frequency. In Exp. 1 and 2, Angus-cross cycling beef heifers (n = 22 and 38, respectively) were allotted to 1 of 2 treatments: 1) heifers received an injection of PGF(2α) on d -3, an injection of GnRH and insertion of a CIDR on d 0, and a PGF(2α) injection and CIDR removal on d 6 (PG-CIDR) or 2) an injection of GnRH and insertion of a CIDR on d 0 and on d 7 an injection of PGF(2α) and removal of CIDR (Select Synch + CIDR). In Exp. 3, Angus-cross beef heifers (n = 15) were assigned to 1 of 3 treatments: 1) PG-CIDR; 2) PGF(2α) on d -3, GnRH on d 0, and PGF(2α) on d 6 (PG-No CIDR); or 3) Select Synch + CIDR. Follicular development and ovulatory response were determined by transrectal ultrasonography. Across all experiments, more (P = 0.02) heifers treated with PG before GnRH initiated a new follicular wave after the injection of GnRH compared with Select Synch + CIDR-treated heifers. In Exp. 1, after CIDR removal, interval to estrus did not differ (P = 0.18) between treatments; however, the variance for the interval to estrus was reduced (P < 0.01) in PG-CIDR heifers compared with Select Synch + CIDR heifers. In Exp. 3, there was a tendency (P = 0.09) for LH pulse frequency to be greater among PG-CIDR and PG-No CIDR compared with the Select Synch + CIDR, but area under the curve, mean LH concentrations, and mean amplitude did not differ (P > 0.76). In summary, induction of luteal regression before an injection of GnRH increased the percentage of heifers initiating a new follicular wave. Removal of endogenous progesterone tended to increase LH pulse frequency, and the modified treatment increased the synchrony of estrus after CIDR removal.

Deciphering the luteal transcriptome: potential mechanisms mediating stage-specific luteolytic response of the corpus luteum to prostaglandin F2α

The objective of this study was to identify prostaglandin F2α (PG)-induced changes in the transcriptome of bovine corpora lutea (CL) that are specific to mature, PG-responsive (day 11) CL vs. developing (day 4) CL, which do not undergo luteolysis in response to PG administration. CL were collected at 0, 4, and 24 h after PG injection on days 4 and 11 of the estrous cycle ( n = 5 per day and time point), and microarray analysis was performed with GeneChip Bovine Genome Arrays. Data normalization was performed with affy package and significance testing with maanova from Bioconductor. Significance (relative to 0 h time point) was declared at fold change >2.0 or <0.5 and false discovery rate of <5%. At 4 and 24 h after PG, 221 (day 4) and 661 (day 11) and 248 (day 4) and 1,421 (day 11) regulated genes, respectively, were identified. The accentuated gene expression response in day 11 CL was accompanied by specific enrichment of PG-regulated genes in distinctive gene ontology categories (immune related and other), particularly at 24 h after injection. Specificity in putative transcription factor binding sites was observed among PG-regulated genes on day 11 vs. day 4, including a potential association of ETS transcription factors with acute PG-induced gene expression specific to day 11 CL. Temporal and PG-induced regulation of abundance of mRNA for ETS transcription factor family members linked to the stage-specific response to PG was not observed. Increased abundance of protein and/or mRNA for six PG-regulated putative ETS-responsive genes was noted in day 11 but not day 4 CL. Results reveal insight into stage-specific gene expression in bovine CL in response to PG and potential transcriptional mediators of luteolysis.