Variation in Duration of Estrus. Dr. Michael Smith, Un. of Missouri August 17, Overview. Ovarian Structures Graffian follicle.

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1 Dr. Michael Smith, Un. of Missouri August 17, 15 Overview Establishment of Pregnancy in Beef Cattle: Application of Basic Principles M.F. Smith 1, G.A. Perry, K.G. Pohler 1, S.E. Dickinson 1, and D.J. Patterson 1 1 Division of Animal Sciences, University of Missouri Department of Animal and Range Sciences, South Dakota State University Characteristics of the estrous cycle. How does the estrous cycle work in a cow? Hormonal changes required to establish pregnancy. Estrous synchronization products How do they work? Physiological factors affecting pregnancy rate to FTAI. Characteristics of the Estrous Cycle Length of the estrous cycle Average 1 days (range 17 to days) Two follicular waves 17 to days Three follicular waves 1 to days (standing heat) 1 to 1 hours (range to 3 hours) Approximately 3 hours after the beginning of standing estrus Variation in Duration of Ovarian Structures Graffian follicle Corpus luteum White et. al., 15 ARSBC, UC-Davis 1

2 Dr. Michael Smith, Un. of Missouri August 17, 15 Dominance Hormone concentration The Estrous Cycle Atresia Selection Recruitment CL Progesterone Hormones utilized in Synchronization Protocols Progesterone/Progestins Prostaglandin F α ARSBC, UC-Davis

3 Dr. Michael Smith, Un. of Missouri August 17, 15 Elevated Progesterone Prebreeding Elevated Progesterone Prebreeding Blocks estrus Blocks ovulation Prepares for pregnancy Induces cyclicity Progestins Melengestrol Acetate - MGA Controlled Internal Drug Release - CIDR 15 ARSBC, UC-Davis 3

4 Dr. Michael Smith, Un. of Missouri August 17, 15 Importance of Progesterone for Cyclicity 5 Progesterone (ng/ml) Day Induction of and FTAI Pregnancy rate in Anestrous Cows Progesterone (ng/ml) 5 Or 3 CIDR Day 31 Cows Studies Bader et al., 5 Schafer et al., 7 Busch et al., Wilson et al., Estrous Cycling - 139/31 = 57% Anestrus 1/31 = 3% Estrous Cycling Anestrus MGA-PG Protocol for Heifers Inhibition of Following Long-term Progestin Treatment MGA Select 1-d CIDR Feed MGA 19 days Treatment day PG 7 ± hr + AI Progestin Treatment MGA for 1 days CL Regressed (less fertile) 15 ARSBC, UC-Davis

5 Dr. Michael Smith, Un. of Missouri August 17, 15 Follicular Wave Length and Fertility Follicular Wave Length and Fertility MGA PGF Preg Rate = 1% Patterson et al, 199 Follicular Wave Length and Fertility MGA PGF Synchronization of Follicular Waves PGF MGA Preg Rate = 1% Patterson et al, 199 Progesterone Must Decrease before AI Permit estrous expression Permit ovulation Allow increased estradiol Prostaglandin F α (PGF α ) Causes CL regression No effect on noncycling cattle No induction of cyclicity No Jump-start Effective days to 1 of the estrous cycle (day = estrus) 15 ARSBC, UC-Davis 5

6 Dr. Michael Smith, Un. of Missouri August 17, 15 PGF α Effect of Stage of the Cycle Increased Estradiol Before AI Is Essential NO NO Sperm transport Signal for ovulation YES Effect of Expression on Pregnancy Rate -Induced During a Follicular Wave NO YES NO YES A Surge of LH is Required for A surge of LH is Required for Oocyte CL formation 15 ARSBC, UC-Davis

7 Dr. Michael Smith, Un. of Missouri August 17, 15 A Rapid Rise in Progesterone is Important For the Establishment of Pregnancy A Rapid Rise in Progesterone is Important For the Establishment of Pregnancy Promotes embryo growth Maintains pregnancy Effect of Pregnancy Status on Progesterone n = n = to -1 Factors Affecting Pregnancy Rate Progesterone at PGF Follicle Size at AI Pregnancy Rate AI Estradiol at AI Progesterone after AI Atkins et al 13 Take-home Messages Specific hormonal changes during the estrous cycle are required for pregnancy to be established. Estrous synchronization protocols mimic the preceding hormonal changes. Therefore, estrous synchronization products must be administered at the proper dose and at the correct time. Take-home Messages Cycling and noncycling females are present at the start of the breeding season. Consequently, a progestogenbased protocol should be used. Fixed-time AI protocols require synchronization of a follicular wave and control of corpus luteum lifespan. Attention to detail is critical for success. 15 ARSBC, UC-Davis 7

8 Dr. Michael Smith, Un. of Missouri August 17, 15 Induced Surge of LH Injection LH Surge to Hours after injection to 3 Time of Insemination for FTAI VariaJon in Time of OvulaJon 1-day CIDR-PG 5 hr Leitman et al. (9a) 5 Leitman et al. (9b) Mallory et al. (9) 35 n = heifers White et. al., 15 ARSBC, UC-Davis NR Hours After Prostaglandin Fα on HeatWatch n = heifers