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Influence of a CIDR after fixed-time AI on pregnancy rates and returns to estrus of nonpregnant cows

J.E. Larson^*, K.N. Thielen^*, B.J. Funnell^*, J.S. Stevenson, D.J. Kesler and G.C. Lamb

^* North Central Research and Outreach Center, University of Minnesota, Grand Rapids, 55744 , Department of Animal Sciences and Industry, Kansas State University, Manhattan, 66506-0201 , Department of Animal Sciences, University of Illinois, Champaign, 61801 North Florida Research and Education Center, University of Florida, Marianna, 32446

gclamb{at}ufl.edu

Abstract

We determined whether an ovulatory estrus could be resynchronized in previously synchronized, artificially inseminated (AI) nonpregnant cows without compromising pregnancy from the previous synchronized ovulation or to those inseminated at the resynchronized estrus. Ovulation was synchronized in 937 suckled beef cows at 6 locations using a CO-Synch + progesterone insert (controlled internal drug release; CIDR) protocol (a 100-µg injection of GnRH at the time of progesterone insert, followed in 7 d by a 25-mg injection of PGF₂ at insert removal; at 60 h after PGF_2, cows received a fixed-time AI [TAI] plus a second injection of GnRH). After initial TAI, the cows were assigned randomly to 1 of 4 treatments: 1) untreated (control; n = 237); 2) progesterone insert at 5 d after TAI and removed 14 d after TAI (CIDR5-14; n = 234); 3) progesterone insert placed at 14 d after TAI and removed 21 d after TAI (CIDR14-21; n = 232); or 4) progesterone insert at 5 d after TAI and removed 14 d after TAI and then a new CIDR inserted at 14 d and removed 21 d after TAI (CIDR5-21; n = 234). After TAI, cows were observed twice daily until 25 d after TAI for estrus and inseminated according to the AM-PM rule. Pregnancy was determined at 30 and 60 d after TAI to determine conception to the first and second AI. Pregnancy rates to TAI were similar for control (55%), CIDR5-14 (53%), CIDR14-21 (48%), and CIDR5-21 (53%). A greater (P < 0.05) proportion of nonpregnant cows were detected in estrus in the CIDR5-21 (76/110, 69%) and CIDR14-21 (77/120, 64%) treatments than in controls (44/106, 42%) and CIDR5-14 (39/109, 36%) cows. Although overall pregnancy rates after second AI service were similar, combined conception rates of treatments without a CIDR from d 14 to 21 (68.7% [57/83]; Control and CIDR5-14 treatments) were greater (P = 0.03) than those with a CIDR during that same interval (53.5% [82/153]; CIDR5-21 and CIDR14-21 treatments). We conclude that placement of a progesterone insert 5 d after a TAI did not compromise or enhance pregnancy rates to TAI; however, conception rates of nonpregnant cows inseminated after a detected estrus were compromised when resynchronized with a CIDR from d 5 or 14 until 21 d after TAI.

Key Words: artificial insemination • CIDR • estrus synchronization • resynchronization

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