118 A comparison of intravaginal progesterone devices for fixed-time artificial insemination in beef cattle

2021 ◽  
Vol 33 (2) ◽  
pp. 167
Author(s):  
E. M. Zwiefelhofer ◽  
S. X. Yang ◽  
M. Asai-Coakwell ◽  
M. G. Colazo ◽  
J. Hellquist ◽  
...  
Keyword(s):  
Artificial Insemination ◽  
Animal Health ◽  
Colour Change ◽  
Fixed Time ◽  
Device Removal ◽  
Beef Heifers ◽  
Lactating Cows ◽  
Pregnancy Status ◽  
Gonadotrophin Releasing Hormone ◽  
Follicular Dynamics

Intravaginal progesterone (P4) devices used for ovarian synchronization before fixed-time AI (FTAI) differ in drug release, which may influence fertility outcome. A 2×2 study was designed to determine the effects of different intravaginal devices (PRID Delta, 1.55g of P4 vs. CIDR, 1.38g of P4) and parity (heifers vs. cows) on follicular dynamics, expression of oestrus, and pregnancy per AI (P/AI). At random stages of the oestrous cycle, nulliparous beef heifers and lactating cows were given 100µg of gonadorelin (gonadotrophin-releasing hormone, GnRH) intramuscularly (IM) and assigned randomly to either the PRID (n=76 heifers, 76 multiparous, 27 primiparous) or CIDR (n=76 heifers, 73 multiparous, 32 primiparous) group. Devices were removed 5 days later, an oestrus-detection patch was applied just cranial to the tail head, and 500µg of cloprostenol was given IM at the time of device removal and again 24h later. At 72h after device removal, cattle were inseminated and given 100µg of GnRH IM. Transrectal ultrasonography was used to determine the diameter of the largest follicle on the day of device removal and at FTAI, ovulation time, and pregnancy status 30 days after FTAI. A colour change of ≥50% of the oestrus-detection patch at FTAI was taken as expression of oestrus. Data were compared among groups by 2-way ANOVA using MIXED and GLIMMIX procedures. There were no interactions between P4 device and parity for any endpoint. The diameter of the largest follicle (mean±s.e.m.) was not different between PRID and CIDR groups on either the day of device removal (10.6±0.1 vs. 10.9±0.1mm) or the day of FTAI (13.7±0.1 vs. 13.9±0.1mm). The proportion displaying oestrus did not differ between P4 device groups, but was greater in heifers than in cows [121/152 (79.6%) vs. 135/207 (65.2%); P<0.01], and the interval from FTAI to ovulation was shorter in heifers than in cows (27.8±1.2 vs. 32.0±1.1 h; P=0.01). The P/AI was not different between P4 device groups or parity groups (overall 67.0%, 238/355). However, among lactating cows, the P/AI tended to be greater in the PRID vs. CIDR group [75/102 (73.5%) vs. 64/105 (61.0%); P=0.10], and was greater in multiparous vs. primiparous cows [106/148 (71.6%) vs. 33/59 (55.9%); P=0.04]. Among cattle that displayed oestrus, the P/AI tended to be greater in the PRID vs. CIDR group [92/123 (74.8%) vs. 85/131 (64.9%); P=0.09]. Among lactating cows that displayed oestrus, the P/AI was greater in multiparous vs. primiparous cows [74/94 (78.2%) vs. 24/42 (57.1%); P<0.01]. In summary, follicular dynamics and expression of oestrus did not differ between PRID and CIDR groups, but the P/AI tended to be greater in PRID-treated lactating cows and in cattle that displayed oestrus. This research was supported by CEVA Animal Health, Saskatchewan ADF, Agriculture and Agri-Foods Canada, and Rockway Inc.

109 Pre-synchronization and reutilization of progesterone devices during a 6-day CO-Synch protocol for fixed-time artificial insemination in beef heifers

2021 ◽  
Vol 33 (2) ◽  
pp. 161
Author(s):  
E. R. Canadas ◽  
B. J. Duran ◽  
G. Machado ◽  
A. Nall ◽  
S. E. Battista ◽  
...  
Keyword(s):  
Artificial Insemination ◽  
Mixed Models ◽  
Generalized Linear Mixed Models ◽  
Fixed Time ◽  
P Value ◽  
Beef Heifers ◽  
Follicle Diameter ◽  
Follicle Size ◽  
Gonadotrophin Releasing Hormone ◽  
Intravaginal Device

Ovulatory response to the initial gonadotrophin-releasing hormone (GnRH) of the CO-Synch protocol is affected by circulating progesterone (P4) and follicle size. In addition, heifers that ovulate to the initial GnRH treatment have greater fertility after AI. Thus, this study determined the effect of (1) presynchronization (Presynch) before a 6-day CO-Synch protocol and (2) circulating [RCE1] (P4) on ovulatory response, oestrus expression, and pregnancies per AI (P/AI) in beef heifers. Yearling beef heifers (n=233) at three locations were randomly assigned in a 2×2 factorial design to the following treatments: (1) Presynch+6-day CO-Synch with a new P4 device; (2) Presynch+6-day CO-Synch with a once-used P4 device; (3) 6-day CO-Synch with a new P4 device; and (4) 6-day CO-Synch with a once-used P4 device. Presynch consisted of insertion of a new P4 intravaginal device (1.38g of P4) on Day −17 and removal of P4 device on Day −11 concurrently with 500µg of cloprostenol sodium (PGF). On Day −9, all heifers received either a new (New) or once-used (Used) CIDR and 100µg of gonadorelin acetate (GnRH). Six days later (Day −3), CIDRs were removed, 1000µg of PGF was administered and an oestrous detection patch applied (Estrotect). At 72h after CIDR removal, AI was performed concurrently with administration of 100µg of GnRH. Pregnancy was determined by transrectal ultrasonography 31 days after AI. A subset of heifers (n=155) was examined on Day −9 and Day −3 by ultrasonography to determine ovulation to Day −9 GnRH. Data were analysed using generalized linear mixed models (SAS 9.4; SAS Institute Inc.). Presynch heifers had larger follicle diameter on Day −9 (12.7±0.3 vs. 10.1±0.3 mm; P<0.001), greater ovulatory response to Day −9 GnRH (82.5%; 66/80 vs. 56%; 42/75; P<0.001), greater expression of oestrus (90.6%; 106/117 vs. 78.4%; 91/116; P<0.02), and earlier oestrus (49.8±1 vs. 53.1±1 h; P<0.01) compared with controls. There was a treatment×CIDR interaction on oestrous expression, such that a lesser (P<0.05) percentage of control heifers with new CIDR expressed oestrus compared with all other groups (Table 1). Heifers with a used CIDR during the 6-day CO-Synch tended (P=0.08) to have greater P/AI (52.1%; 61/117) than those with a new CIDR (40.5%; 47/116). In conclusion, presynchronization before initiation of a 6-day CO-Synch increased follicle diameter, enhanced ovulatory response and oestrous expression, but did not affect fertility. The earlier onset of oestrus in presynchronized heifers suggests that the timing of AI may need to be modified. Table 1. Oestrous expression and pregnancy per AI (P/AI) in beef heifers with or without presynchronization and treated with a new or used CIDR during a 6-day CO-Synch Treatment CIDR Oestrus (%; n/n) Time of oestrus (h) P/AI (%; n/n) Control New 67.8a (40/59) 53.7±1.5a 33.9 (20/59) Used 89.5b (51/57) 52.7±1.6a 50.9 (29/57) Presynch New 94.7b (54/57) 50.9±1.4b 47.4 (27/57) Used 86.7b (52/60) 48.7±1.3b 53.3 (32/60) P-value Treatment 0.03 0.01 0.21 CIDR 0.62 0.19 0.08 Interaction 0.003 0.75 0.38 a,bValues with different superscripts differ (P<0.05).

160 Increasing gonadotrophin-releasing hormone dose at initiation of a 5-day CO-Synch protocol increases ovulatory response but not fertility in yearling beef heifers

2020 ◽  
Vol 32 (2) ◽  
pp. 206
Author(s):  
E. Rojas Canadas ◽  
S. E. Battista ◽  
J. Kieffer ◽  
S. Wellert ◽  
A. Garcia Guerra
Keyword(s):  
Dose Group ◽  
Fixed Time ◽  
Ovulation Rate ◽  
Corpora Lutea ◽  
Double Dose ◽  
Device Removal ◽  
Beef Heifers ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
To Receive

Heifers typically have a reduced ovulation rate following gonadotrophin-releasing hormone (GnRH) application at initiation of a CO-Synch + controlled internal drug release (CIDR) protocol. Thus, the objective of the present study was to determine whether increasing the dose of GnRH at initiation of a 5-day CO-Synch protocol in beef heifers would improve ovulation rate and therefore increase pregnancies per AI (P/AI). Angus yearling heifers (n=299) at five locations in Ohio (United States) were randomised to receive either 100µg (single; n=149) or 200µg (double; n=150) of gonadorelin acetate (Gonabreed, Parnell) at initiation of a 5-day CO-Synch. On Day −8, heifers received a new intravaginal progesterone-releasing device (1.38g of progesterone; CIDR, Zoetis) and either a single or double dose of GnRH as described above. Five days later (Day −3), devices were removed, 1000µg of cloprostenol sodium (Estroplan, Parnell) was administered, and an oestrous detection patch was applied (Estrotect, Rockway Inc.). Sixty hours after device removal, AI was performed concurrently with the administration of 100µg of GnRH. Pregnancy was determined using ultrasonography 35 days after AI. Ovaries from a subset of animals (n=178) were examined on Days −8 and −3 using ultrasonography to determine the presence of corpora lutea (CL) and the size of the largest follicle. Data were analysed using the GLIMMIX procedure of SAS ver. 9.4 (SAS Institute Inc.). Oestrous expression was similar (P=0.50) between heifers treated with a single (49.0%) or double (52.7%) dose of GnRH. Overall, P/AI was similar (P=0.35) between heifers receiving a single (43.6%; 65/149) or double (38.7%; 58/150) dose of GnRH at initiation of the protocol. However, increasing the dose of GnRH resulted in a greater (P=0.04) ovulation rate in heifers in the double-dose group (40.9%; 36/88) compared with those in the single-dose group (26.1%; 23/88). In addition, heifers with a CL at the time of treatment had reduced ovulatory response to GnRH treatment (16.0%) compared with heifers without a CL (53.7%; P=0.001); however, there was no treatment×CL presence interaction (P=0.69). Heifers that did not ovulate to the initial GnRH treatment had a greater (P=0.0008) diameter of the largest follicle on Day −3 compared with heifers that did ovulate (11.4±0.2 vs. 10.0±0.3). Furthermore, heifers that did ovulate after the initial GnRH had greater (P=0.04) P/AI (52.5%) than heifers that did not ovulate (40.2%), and heifers with a CL on Day −8 tended (P=0.07) to have greater P/AI (47.9%) than heifers without a CL (40.2%). In addition, heifers with a CL present on Day −3 had greater (P=0.04) P/AI (48.2%) than heifers without a CL (31.7%). In summary, increasing the dose of GnRH at initiation of a 5-day CO-Synch did not affect fertility to fixed-time AI but enhanced ovulation rate in beef heifers. Furthermore, heifers that did ovulate at initiation of the protocol or that had a CL at device insertion or removal had greater fertility to fixed-time AI. Thus, alternative strategies that maximise ovulation at initiation of the synchronisation protocol are needed.

115 Presynchronization and reutilization of progesterone devices during a 6-day CO-Synch protocol for fixed-time artificial insemination in beef heifers

2021 ◽  
Vol 33 (2) ◽  
pp. 165
Author(s):  
E. R. Canadas ◽  
B. Duran ◽  
G. Machado ◽  
A. Nall ◽  
S. E. Battista ◽  
...  
Keyword(s):  
Factorial Design ◽  
Artificial Insemination ◽  
Fixed Time ◽  
P Value ◽  
Beef Heifers ◽  
Follicle Diameter ◽  
Follicle Size ◽  
Gonadotrophin Releasing Hormone ◽  
Intravaginal Device ◽  
Second Use

Ovulatory response to the initial gonadotrophin-releasing hormone (GnRH) of the CO-Synch protocol is affected by circulating progesterone (P4) and follicle size. In addition, heifers that ovulate to initial GnRH treatment have greater fertility after AI. Thus, the aim of this study was to assess the effect of (1) presynchronization (Presynch) before a 6-day CO-Synch protocol and (2) P4 device reuse (new vs. second use) on ovulatory response, oestrous expression, and pregnancy per AI (P/AI) in beef heifers. Yearling beef heifers (n=233) were randomly assigned in a 2×2 factorial design to the following treatments: (1) Treatment (Presynch): (1a) Presynch+6-day CO-Synch with new P4 device; (1b) Presynch+6-days CO-Synch with a once-used P4 device; (2) Control (no Presynch): (2a) 6-day CO-Synch with new P4 device; (2b) 6-day CO-synch with once-used P4 device. Presynch consisted of insertion of a new P4 intravaginal device (CIDR, 1.38g of P4; Zoetis) on Day −17 and removal of the CIDR on Day −11 concurrently with 500µg of cloprostenol sodium. On Day −9, all heifers received either a new or once-used (used) CIDR and 100µg of gonadorelin acetate (GnRH, Parnell Inc.). Six days later (Day −3) CIDRs were removed, 1000µg of PGF was administered, and an oestrous detection patch applied (Estrotect, Rockway Inc.). At 72h after CIDR removal, 100µg of GnRH and AI using 3 different sires was performed. Pregnancy was determined by ultrasonography 31 days after AI. A subset of heifers (n=151) were examined on Day −9 and Day −3 by ultrasonography to assess ovulation to Day −9 GnRH. Data were analysed using GLIMMIX (SAS 9.4; SAS Institute Inc.). Presynch heifers had larger follicle diameter on Day −9 (12.7±0.3 vs. 10.4±0.3 mm; P<0.0001), greater ovulatory response (84.6%; 66/78 vs. 52.05%; 38/73; P<0.0001), greater oestrus expression (90.6%; 106/117 vs. 78.4%; 91/116; P=0.03), and expressed oestrus earlier (49.8±1.0 vs. 53.1±1.1 h; P=0.01) compared with controls. There was an interaction for treatment and CIDR on oestrous expression, whereas a lesser (P=0.003) percentage of control heifers with new CIDR showed oestrus compared with all other groups (Table 1). Heifers treated with a used P4 device tended (P=0.08) to have greater P/AI (52.1%; 61/117) than those with a new CIDR (40.5%; 47/116). In conclusion, presynchronization before initiation of a 6-day CO-Synch increased follicle diameter, ovulatory response, and oestrous expression, but did not affect fertility. The earlier onset of oestrus in Presynch heifers warrants further study on timing of AI. Table 1. Oestrous expression and pregnancy per AI (P/AI) in beef heifers with or without presynchronization and treated with a new or used CIDR Treatment CIDR Oestrus (%; n/n) Time of oestrus (h) P/AI (%; n/n) Control New 67.8a (40/59) 53.7±1.5a 33.9 (20/59) Used 89.5b (51/57) 52.7±1.6a 50.9 (29/57) Presynch New 94.7b (54/57) 50.9±1.4b 47.4 (27/57) Used 86.7b (52/60) 48.7±1.3b 53.3 (32/60) P-value Treatment 0.03 0.01 0.21 CIDR 0.62 0.18 0.08 Interaction 0.003 0.78 0.38 a,bValues with different superscripts differ (P < 0.05).

Influence of the male effect on follicular dynamics and pregnancy rate in lactating cows undergoing fixed-time artificial insemination

2020 ◽  
Vol 240 ◽  
pp. 104148
Author(s):  
Manoel Lopes Silva Filho ◽  
José Carlos Ferreira-Silva ◽  
Joane Isis Travassos Vieira ◽  
Sarah Romini Lima Basto ◽  
Maiana Silva Chaves ◽  
...  
Keyword(s):  
Pregnancy Rate ◽  
Artificial Insemination ◽  
Fixed Time ◽  
Lactating Cows ◽  
Male Effect ◽  
Follicular Dynamics

scholarly journals 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

Animals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 849
Author(s):  
Aitor Fernandez-Novo ◽  
Sergio Santos-Lopez ◽  
Jose Luis Pesantez-Pacheco ◽  
Natividad Pérez-Villalobos ◽  
Ana Heras-Molina ◽  
...  
Keyword(s):  
Animal Welfare ◽  
Reproductive Performance ◽  
Artificial Insemination ◽  
Fixed Time ◽  
Reproductive Efficiency ◽  
Beef Heifers ◽  
Animal Management ◽  
Commercial Farms ◽  
Beef Herds ◽  
Farm Economics

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.

Response of beef heifers and non-suckling beef cows to different oestrous synchronization protocols

2002 ◽  
Vol 74 (3) ◽  
pp. 547-552 ◽  
Author(s):  
D. Cavestany ◽  
N. Negrin ◽  
R. Negrin ◽  
J. F. Groth
Keyword(s):  
Beef Cattle ◽  
Medroxyprogesterone Acetate ◽  
Artificial Insemination ◽  
Experimental Period ◽  
Fixed Time ◽  
Beef Cows ◽  
Pregnancy Rates ◽  
Gnrh Analogue ◽  
Beef Heifers

AbstractThe objective was to evaluate different oestrous synchronization schemes in beef cattle under range conditions. In experiment 1, 202 heifers averaging 26 months of age were assigned randomly to three treatments: (a) GnRH-PG. (no. = 44) day 0 (D0): injection of GnRH; D7: injection of PGF2α; D0 to D25 oestrous detection (OD) and artificial insemination (AI); (b) OD-PG. (no. = 45) D0 to D4; OD + AI; D5: injection of PGF2α; D5 to D25 OD + AI; and (c)Ovsynch. (no. = 113) D0: injection of GnRH; D7: injection of PGF2α; D9: injection of GnRH and 16 h later AI at fixed time. In experiment 2, 318 non-suckling cows were assigned randomly to three treatments: (a) GnRH-PG. (no. = 106) D0: injection of GnRH; D7: injection of PGF2α; D0 to D25 OD + AI; (b) GnRH-MAP-PG. (no. = 106) D0: injection of a GnRH analogue and insertion of an intravaginal sponge impregnated with 250 mg of medroxyprogesterone acetate; D7: injection of PGF2α and sponge withdrawal; D0 to D25 OD + AI; (c) controls. (no. = 106) OD and AI. The experimental period lasted 25 days and, with exception of the Ovsynch treatment, oestrous detection was carried out twice a day (a.m./p.m.) and inseminations performed 12 h later. The pregnancy rates assessed by ultrasonography 30 days after AI were: experiment 1: (a) 30·0%; (b) 28·6% and (c) 62·3% (P < 0·05); experiment 2: (a) 60·2%; (b) 57·8% and (c) 45·5% (P < 0·05). It is concluded that in heifers and non-suckling cows, oestrous synchronization treatments result in higher pregnancy rates. In non-suckling cows, the addition of a progestagen did not improve the response.

Efficiency of mating, artificial insemination or resynchronisation at different times after first timed artificial insemination in postpartum Nellore cows to produce crossbred calves

2019 ◽  
Vol 59 (2) ◽  
pp. 225 ◽  
Author(s):  
Walvonvitis Baes Rodrigues ◽  
Jean do Prado Jara ◽  
Juliana Correa Borges ◽  
Luiz Orcirio Fialho de Oliveira ◽  
Urbano Pinto Gomes de Abreu ◽  
...  
Keyword(s):  
Pregnancy Rate ◽  
Breeding Season ◽  
Chorionic Gonadotropin ◽  
Artificial Insemination ◽  
Fixed Time ◽  
Beef Cows ◽  
Device Removal ◽  
Oestradiol Benzoate ◽  
Timed Artificial Insemination ◽  
Equine Chorionic Gonadotropin

The objective of this trial was to evaluate different post-timed artificial insemination (TAI) reproductive managements in postpartum beef cows to produce crossbred calves from artificial insemination (AI). Nellore cows (n = 607), with 45 days postpartum, were inseminated at a fixed time, using a protocol that included an intravaginal progesterone-releasing device along with oestradiol benzoate, prostaglandin, equine chorionic gonadotropin, and oestradiol cypionate, followed TAI 48 h post-device removal. Four post-TAI treatments were evaluated: in CONTROL (T1, n = 161), cows were exposed to Nellore clean-up bulls until the end of the breeding season (75 days). In OBSERVATION (T2, n = 132), heat detection was performed for 15–25 days post-TAI, followed by AI. In RESYNC22 (T3, n = 157) and RESYNC30 (T4, n = 157), resynchronisation started after 22 or 30 days, following second TAI at Day 32 or 40 days after first TAI. In T2, T3 and T4, after the second AI, cows were exposed to Nellore clean-up bulls until the end of the breeding season (75 days). The pregnancy rate (PR) for the first TAI did not differ (54.6%, 53.0%, 59.2%, and 51.6% for CONTROL, OBSERVATION, RESYNC 22, and RESYNC 30, respectively; P = 0.66), and no difference was observed for the second TAI (RESYNC 22 = 45.31% and RESYNC30 = 46.05%; P = 0.137), in the PR at the end of the breeding season (86.33%, 86.36%, 78.98%, and 81.52%, P = 0.43), or embryonic losses (4.54%, 2.85%, 6.45% and 7.40%, respectively; P = 0.61), but the percentage of crossbred pregnancy was higher in groups with resynchronisation (RESYNC22 and RESYNC30) than CONTROL and OBSERVATION (98.38%, 90.62%, 63.30%, 78.95%, P &lt; 0.001). In conclusion, resynchronisation programs of 22 or 30 days are more efficient to produce AI products, and the final pregnancy rate is similar among the treatments, differing only in the amount of calves produced by AI.

068 Utilization of resynchronization as a strategy to increase the percentage of replacement beef heifers conceiving to artificial insemination (AI) after an initial fixed-time AI (TAI)

2016 ◽  
Vol 94 (suppl_1) ◽  
pp. 34-34
Author(s):  
P. L. P. Fontes ◽  
N. Oosthuizen ◽  
V. R. G. Mercadante ◽  
G. V. de Moraes ◽  
D. D. Henry ◽  
...  
Keyword(s):  
Artificial Insemination ◽  
Fixed Time ◽  
Beef Heifers

7 PREGNANCY RATES IN BEEF HEIFERS SYNCHRONIZED WITH A SHORTENED OESTRADIOL-BASED TREATMENT THAT PROVIDES FOR A PROLONGED PROESTRUS

2015 ◽  
Vol 27 (1) ◽  
pp. 96 ◽  
Author(s):  
A. Menchaca ◽  
R. Nuñez-Olivera ◽  
F. Cuadro ◽  
G. Bo
Keyword(s):  
Treatment Group ◽  
Day Treatment ◽  
Fixed Time ◽  
Gonadotropin Releasing Hormone ◽  
Pregnancy Rates ◽  
Device Removal ◽  
Beef Heifers ◽  
Releasing Hormone ◽  
Secondary Objective ◽  
To Receive

An oestradiol-based protocol (named J-Synch) has been developed recently with the aim of providing for a longer proestrus, enhancing the development of the dominant follicle before ovulation, and increasing pregnancy rates following fixed-time AI (FTAI) in heifers (de la Matta and Bo 2012 Taurus 55, 17–23). Two experiments were performed in Uruguay with 1953 Angus × Hereford crossbred heifers to compare pregnancy rates obtained with the J-Synch protocol with the conventional 7-day oestradiol-based protocol. A secondary objective was to determine the effects of the time of FTAI and the addition of eCG at the time progestin device removal on pregnancy rates. In Experiment 1, 966 heifers received a DIB device (0.5 g of progesterone, Syntex, Buenos Aires, Argentina) plus 2 mg of oestradiol benzoate IM (Syntex) on Day 0. Heifers in the conventional treatment group (n = 485) received cloprostenol (500 μg, Ciclase DL, Syntex) and oestradiol cypionate (0.5 mg, Cipiosyn, Syntex) IM and had their DIB removed on Day 7 a.m. Heifers in this group were then subdivided to be FTAI on Day 9 a.m. or p.m. (i.e. 48 or 56 h after DIB removal). Heifers in the J-Synch treatment group (n = 481) received cloprostenol IM and DIB removal on Day 6 p.m. and received gonadotropin-releasing hormone (100 μg gonadorelin acetate, Gonasyn Gdr, Syntex) on Day 9 a.m.; heifers were then FTAI on Day 9 a.m. or p.m. (i.e. 60 or 72 h after DIB removal). All heifers in this experiment were also treated with 300 IU of eCG (Novormon, Syntex) at DIB removal. In Experiment 2, 987 heifers were treated with the J-Synch protocol as described in Experiment 1. At device removal (Day 6 p.m.), heifers were divided to receive (n = 488) or not (n = 499) 300 IU of eCG IM at that time and were further subdivided to receive gonadotropin-releasing hormone and FTAI on Day 9 a.m. or p.m. (i.e. 60 or 72 h after DIB removal). Pregnancy rates were determined by ultrasonography 30 days after FTAI. Data were analysed using logistic regression, and results are shown in Table 1. J-Synch-treated heifers tended (P < 0.1) to have higher pregnancy rates following FTAI, whereas time of FTAI only affected pregnancy rates following the conventional 7-day treatment (P < 0.05). However, removal of eCG from the J-Synch protocol in Experiment 2 resulted in reduced pregnancy rates when inseminations were done on Day 9 p.m. (P < 0.05). In summary, the addition of eCG to the J-Synch protocol provided for a wider window of insemination times facilitating FTAI in large groups of beef heifers. Table 1.Effect of length of progestin insertion, time of insemination and eCG treatment on pregnancy rates in beef heifers

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