Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2005
Publication Date: 2/1/2006
Citation: Larson, J.E., Lamb, G.C., Stevenson, J.S., Johnson, S.K., Day, M.L., Geary, T.W., Kesler, D.J., Dejarnette, J.M., Schrick, F.N., Arseneau, J.D. 2006. Synchronization of estrus in suckled beef cows before detected estrus and (or) timed artificial insemination using gonadotropin-releasing hormone (gnrh), prostaglandin f2a (pg), and progesterone (cidr). Journal of Animal Science 84:332-342. Interpretive Summary: Optimal pregnancy rates in beef cattle require more than compliance to a sound estrus- synchronization protocol. Estrous cyclicity is a major factor affecting fertility. Body condition, parity, and days postpartum can greatly affect the proportion of cows cycling at the initiation of an estrus-synchronization protocol. Estrus/ovulation was synchronized in 2,598 suckled beef cows from 14 locations with one of five treatments using CIDRs, GnRH, and PGF with breeding by estrus and/or timed AI (TAI) only. We have demonstrated that producers can effectively utilize two strategies to enhance the ease and efficiency of implementation of estrus-synchronization while optimizing pregnancy rates in beef production systems: 1) a strategy that reduces detection of estrus by combining estrus detection with a clean-up TAI; and 2) a fixed TAI protocol that includes a CIDR eliminates detection of estrus with all cows inseminated artificially at a single predetermined time. Both strategies are of short duration (< than 10 d) and limit the frequency that cows are handled, allowing AI to be utilized as a suitable reproductive management tool for producers. Overall, the Select Synch + CIDR & TAI seemed to most consistently yield the greatest pregnancy rates among treatments at most locations.
Technical Abstract: We determined whether a fixed-time artificial insemination (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus and whether adding a CIDR to GnRH + PGF2F (PG)-based protocols would enhance fertility. Estrus in 2,598 suckled beef cows at 14 locations was synchronized and AI was preceded by one of five treatments: 1) a CIDR for 7 d with 25 mg of PG at CIDR removal, followed by detection of estrus and AI during the 84 h after PG; cows not detected in estrus by 84 h received 100 'g of GnRH and TAI at 84 h (Control; n = 506); 2) GnRH administration, followed in 7 d with PG, followed in 60 h by a second injection of GnRH and TAI (CO-Synch; n = 548); 3) CO-Synch plus a CIDR during the 7 d between the first injection of GnRH and PG (CO-Synch + CIDR; n = 539); 4) GnRH administration, followed in 7 d with PG, followed by detection of estrus and AI during the 84 h after PG; cows not detected in estrus by 84 h received GnRH and TAI at 84 h (Select Synch & TAI; n = 507); and 5) Select Synch & TAI plus a CIDR during the 7 d between the first injection of GnRH and PG (Select Synch + CIDR & TAI; n = 498). Blood samples were collected (d –17 and –7, relative to PG) to determine estrus-cycling status. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of cows cycling at the initiation of treatments was 66%. Pregnancy rates among locations ranged from 37% to 67%. Pregnancy rates were greatest for the Select Synch + CIDR & TAI (58%) treatment, although not different from the CO-Synch + CIDR (54%), Select Synch & TAI (53%), or Control (53%), but greater (P < 0.05) than the CO- Synch (44%) treatment. Controls had pregnancy rates similar to those in CO-Synch + CIDR and Select Synch & TAI treatments. Overall, the Select Synch + CIDR & TAI protocol consistently achieved the greatest pregnancy rates among locations; however, CO-Synch + CIDR was a reliable TAI protocol that offers the option to eliminate detection of estrus when inseminating beef cows