
%0 Journal Article
%A Small, J. A. 
%A Colazo, M. G. 
%A Kastelic, J. P. 
%A Ward, D. R. 
%A Dochi, O. 
%A Mapletoft, R. J. 
%T 18 THE EFFECTS OF CIDR AND eCG TREATMENTS IN A GnRH-BASED PROTOCOL FOR TIMED AI OR EMBRYO TRANSFER ON PREGNANCY RATES IN LACTATING BEEF COWS
%J Reproduction, Fertility and Development
%D 2006/12/12
%V 19
%N 1
%P 127-128
%K 
%R https://doi.org/10.1071/RDV19N1AB18
%U https://www.publish.csiro.au/paper/RDV19N1AB18 
%X Two experiments were conducted to determine the effects of the addition of a progestin, equine chorionic gonadotropin (eCG), or both, in a GnRH-based protocol for timed AI (TAI) or timed embryo transfer (TET). In both experiments, Angus, Gelbvieh, and Simmental cross-bred cows were randomized by breed and postpartum interval [50 ± 10 days (mean ± SD); range, 27 to 89] into 4 groups in a 2 × 2 factorial design. All injections were given IM. In Experiment 1, 288 cows (89.6% cycling) were given 25 mg dinoprost (PGF; Lutalyse®; Pfizer Animal Health, Montreal, Quebec, Canada) on Day &#8211;11; on Day 0, they were given 100 µg GnRH (Cystorelin®; Merial Canada, Pointe-Claire, Quebec, Canada), with or without concomitant insertion of a CIDR (1.9 g progesterone; Pfizer Animal Health, Montreal, Quebec, Canada). On Day 7, CIDR inserts were removed and cows were given PGF, with or without concomitant injection of 400 IU of eCG (Pregnecol®; Bioniche Animal Health, Belleville, Ontario, Canada). On Day 9 (54-56 h after PGF), TAI was done, with concomitant injection of 100 µg GnRH. Ultrasonographic examination of 147 cows on Day 7 revealed that 62.4% had ovulated in response to the first GnRH. Pregnancy rates (ultrasonographic examination) on Day 38 did not differ between cows with or without a CIDR (52.9 and 51.4%, rspectively; P &#8805; 0.64), with or without eCG treatment (53.5 and 50.7%, respectively; P &#8805; 0.28), in cycling vs. anestrous cows (51.6 vs 56.7%, respectively; P &#8805; 0.76), and in cows that had ovulated (58.1%) or did not ovulate (50.0%) after the first GnRH treatment (P &#8805; 0.58). In Experiment 2, 151 cows were given 500 µg cloprostenol (PGF; Estrumate®; Schering&#8211;Plough Animal Health, Pointe-Claire, Quebec, Canada) on Day &#8211;12, 100 µg GnRH on Day 0, with or without concomitant insertion of a CIDR. On Day 3, half of the cows were given 400 IU eCG. On Day 7, CIDRs were removed and cows were given PGF; on Day 9 (54&#8211;56 h after PGF), all cows were given 100 µg GnRH. On Day 15, ultrasonography was done to select suitable recipients for transfer of frozen&#8211;thawed embryos on Day 16 (part of another experiment, balanced across synchronization groups). Recipient selection rates did not differ whether cows received or did not receive a CIDR (93.4% vs 85.5%, respectively; P &#8805; 0.27) or eCG (91.0 vs 87.8%, respectively; P &#8805; 0.67). In addition, pregnancy rates on Day 43 did not differ whether cows received or did not receive a CIDR (32.3 vs 32.4%, respectively; P &#8805; 0.52) or eCG (35.2 and 29.2%, respectively; P &#8805; 0.21). In summary, the addition of a CIDR or eCG to a GnRH-based synchronization protocol initiated after PGF presynchronization in lactating beef cattle yielded no improvement in pregnancy rates following TAI, or recipient selection and pregnancy rates following TET. 
