Influence of estrus expression in a fixed-time AI protocol on reproductive performance

Authors: PERRY, GEORGE - South Dakota State University; Cushman, Robert - Bob; NORTHROP, EMMALEE - South Dakota State University; RICH, JERICA - South Dakota State University; PERKINS, STEPHANIE - South Dakota State University

Submitted to: Animal Reproduction
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2018
Publication Date: 9/3/2018
Citation: Perry, G.A., Cushman, R.A., Northrop, E.J., Rich, J.J.J., Perkins, S.D. 2018. Influence of estrus expression in a fixed-time AI protocol on reproductive performance [abstract]. Animal Reproduction. 15(Supplement 1):1141.

Interpretive Summary:

Technical Abstract: The ability to induce ovulation of a dominant follicle with an injection of GnRH facilitated the development of fixed-time AI protocols. However, it has been established that cattle need to experience elevated concentrations of progesterone, a drop in progesterone, and a rise in estradiol to establish timing for changes in uterine gene expression. Animals that exhibit estrus prior to fixed-time AI have greater pregnancy success compared to animals that are induced to ovulate without expressing estrus. Thus, the objective of this study was to determine the impact of estrus expression prior to fixed-time AI on timing of when pregnancy occurred. Data were collected on 4,499 cows (Bos taurus beef animals ages 13 months to 13 years) in 31 different herds. All animals were synchronized using an injection of GnRH at insertion of an intravaginal progesterone device, an injection of prostaglandin F2a at device removal, and an injection of GnRH at time of Al. Estrus expression was determined at time of AI based on activation of estrus detection patches. Bulls remained separated for 10 days after AI, and fetal age was determined by transrectal ultrasonography. Animals were grouped as having conceived to Al, or into each of the possible return estrous cycles (cycle 1-d 10 to 31, cycle 2-d 32 to 53, or cycle 3-d 54 to 75, and cycle 4 after d 75). Data were analyzed using the GLIMMIX procedure of SAS with herd as a random variable. Animals that exhibited estrus before AI had increased (P < 0.01) pregnancy success to AI (64 ± 1.3% vs 45 ± 1.6%, respectively) and during the entire breeding season (93 ± 0.7% vs 89 ± 1.1 %, respectively) compared to animals that did not exhibit estrus. Of the animals that did not conceive to Al but did conceive during the breeding season, more animals that exhibited estrus before AI conceived during cycle 1 (P < 0.0 l; 46 ± 2% vs 34 ± 3%). However, more animals that did not exhibit estrus conceived in cycle 2 (P 0.02; 46 ± 2% vs 39 ± 2%) and 4 (P = 0.01; 6 ± I% vs 3 ± I%). There was no difference in cycle 3 (P 0.15; ll ± 1% and 13 ± 2% for estrus and no estrus, respectively). Overall, animals that exhibited estrus before AI but did not conceive to AI conceived earlier in the breeding season compared to animals that did not exhibit estrus (P < 0.01; cycle 1.71 ± 0.04 vs cycle 1.93 ± 0.04). There was no difference (P = 0.74) in embryonic loss between groups (2.3 ± 0.3% and 2.1 ± 0.4% for estrus and no estrus, respectively). Thus, the ability to induce ovulation is critical for fixed''time AI, but animals that do not exhibit estrus prior to fixed-time AI had decreased AI conception rates, decreased breeding season pregnancy success, and the animals that did conceive did so later in the breeding season compared to animals that did exhibit estrus.