Fertility of Angus cross beef heifers after GnRH treatment on day 23 and timing of insemination in 14-day CIDR protocol

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.

Presynchronization with CIDR, with or without GnRH, prior to CO-Synch in beef heifers

Objectives were to compare ovarian responses and pregnancy per AI (P/AI) in Angus-cross beef heifers (n = 521; 4 locations) synchronized with CIDR-CO-Synch (CCOS) versus CIDR-GnRH-CO-Synch (CGCOS) protocols. Heifers were assigned a reproductive tract score (RTS: 1, immature, acyclic; 5, mature, cyclic), body condition score (BCS: 1, emaciated; 9, obese) and temperament score (0, calm, 1, excitable). Heifers in the CCOS (n = 261) group received a CIDR on Day -20 (removed on Day -13), 100 μg GnRH on Day -10, 25 mg PGF2α on Day -3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Heifers in the CGCOS (n = 260) group received a CIDR on Day -26 (removed on Day -19), 100 μg of GnRH on days -16 and -10, 25 mg of PGF2α on Day -3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Ovarian ultrasonography was done in a subset of heifers (n = 60; 30 in each group) to determine number and size of ovarian follicles and presence of corpus luteum (CL). There was increased (P < 0.05) percentage of heifers with CL in CGCOS group compared to heifers in CCOS group on Day -10 (82.3 vs 68.2%) and on Day -3 (88.3 vs 75.1%). Average size of the largest ovarian follicle on Day 0 was greater for heifers in CGCOS group compared to CCOS group (P < 0.05). However, P/AI did not differ between CCOS and CGCOS groups, 55.0% (143/260) and 59.8% (156/261), respectively (P > 0.1). In conclusion, CIDR presynchronization with or without GnRH (CCOS and CGCOS protocols) in beef heifers resulted in similar P/AI. Adding GnRH to presynchronization with CIDR resulted in more heifers with a CL at PGF2α and increased preovulatory follicle diameter at AI. Future studies are needed with bigger sample size and CIDR + CO-Synch treatment as control to determine economic benefit.

Cyclicity, estrus expression and pregnancy rates in beef heifers with different reproductive tract scores following progesterone supplementation

Two experiments were conducted to determine effects of progesterone (P4) on cyclicity, estrus expression rate (EER) and artificial insemination pregnancy rate (AIPR) in beef heifers with various reproductive tract scores (RTS; 1 to 5; 1, immature, acyclic; 5, mature, cyclic). In Experiment 1, Angus-cross heifers (n = 100, 20 per RTS category; mean (±SEM) age, 15 ± 0.8 mo) were randomly assigned to receive a CIDR (Days -17 to -10) or no CIDR (untreated control), with weekly blood samples and ultrasonography (Days 0-85). Among heifers with RTS 2 to 4, median interval to cyclicity were shorter (P < 0.05) for heifers in CIDR versus control. In Experiment 2, Angus-cross heifers (n = 11,098) were assigned RTS, body condition score (BCS; 1 to 9; 1, emaciated; 9, obese) and temperament score (calm versus excitable). Heifers with RTS 2-5 (n = 10,569) were allocated to CO-Synch (n = 5099) or CO-Synch + CIDR (n = 5470). Estrus was detected until AI (72 h after PGF2α), with pregnancy diagnosis ∼70 d later. Controlling for RTS (P < 0.0001), BCS (P < 0.0001), temperament (P < 0.0001), age (P < 0.0001), treatment by RTS (P < 0.01), treatment by BCS (P < 0.01), and treatment by age, EER differed between CO-Synch and CO-Synch + CIDR (71.0 vs 75.9%, respectively, P < 0.0001). Accounting for RTS (P < 0.0001), BCS (P < 0.0001), temperament (P < 0.0001), age (P < 0.0001), heifers detected in estrus (P < 0.0001), RTS by treatment (P < 0.01), BCS by treatment (P < 0.01), and age by treatment, AIPR differed between CO-Synch versus CO-Synch + CIDR (55.3 vs 61.0%, P < 0.0001). In conclusion, exogenous P4 hastened cyclicity in pre- and peri-pubertal beef heifers. Further, it increased EER and AIPR. However, RTS, BCS and age influenced EER and AIPR. Among RTS 4 and 5, EER was greater for CO-Synch + CIDR vs CO-Synch. Among RTS 3 to 5, AIPR was greater for CO-Synch + CIDR versus CO-Synch. Progesterone status or supplementation at onset of synchronization protocols was critical to pregnancy outcomes, emphasizing heifer development for early puberty or progesterone supplementation.