Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2006
Publication Date: 11/1/2006
Citation: Lamb, G.C., Larson, J.E., Geary, T.W., Stevenson, J.S., Johnson, S.K., Day, M.L., Kesler, D.J., Dejarnette, J.M., Landblom, D.G., Ansotegui, R.P. 2006. Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2, and progesterone. Journal of Animal Science 84(11):3000-3009. Interpretive Summary: We determined whether a fixed-time artificial insemination (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or estrous detection plus TAI, and whether adding a controlled internal device release (CIDR) to GnRH-based protocols would enhance fertility. We have demonstrated that producers can effectively utilize two strategies to enhance the ease and efficiency of implementation of estrous synchronization while optimizing pregnancy rates in beef heifer production systems: 1) a strategy that reduces detection of estrus by combining estrous detection with a clean-up TAI; and 2) a fixed TAI protocol that includes a CIDR eliminates detection of estrus with all heifers inseminated artificially at a single predetermined time. Both strategies are of short duration (< than 10 d) and limit the frequency that heifers are handled, allowing AI to be utilized as a suitable reproductive management tool for producers. The CO-Synch + CIDR protocol yielded similar pregnancy rates to estrous detection protocols and is a reliable TAI protocol that eliminates detection of estrus when inseminating replacement beef heifers.
Technical Abstract: Estrus in 2,075 replacement beef heifers at 12 locations was synchronized and AI was preceded by one of four treatments: 1) heifers received a CIDR insert for 7 d with 25 mg PG on the day of CIDR removal (d 0), followed by detection of estrus and AI during 84 h after PG; heifers not detected in estrus by 84 h received 100 'g of GnRH and TAI (Control; n = 516); 2) Control plus heifers received 100 'g of GnRH at the time of CIDR insertion (Select Synch + CIDR & TAI; n = 503); 3) heifers received a CIDR for 7 d with an injection of PG on the day of CIDR removal, followed in 60 h by a second injection of GnRH and one fixed time AI (CIDR-PG + TAI; n = 525); and, 4) CIDR-PG + TAI plus heifers received GnRH at the time of CIDR insertion (CO-Synch + CIDR; n = 531). Blood samples were collected (d –17 and –7, relative to PG) to determine cycling status. For the Control and Select Synch + CIDR & TAI treatments a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed using the AM/PM rule. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of heifers cycling at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38% to 74%. Pregnancy rates were 54.7, 57.5, 53.1, and 49.3% for Control, Select Synch + CIDR & TAI, CO-Synch + CIDR, and CIDR-PG + TAI treatments respectively. Although pregnancy rates were similar among treatments, there was a tendency for pregnancy rates in the Select Synch + CIDR & TAI treatment to be greater (P = 0.065) than the CIDR-PG + TAI treatment.