Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2003
Publication Date: 6/1/2003
Citation: GEARY, T.W. FERTILITY AND DISTRIBUTION OF ESTRUS AMONG COWS FOLLOWING PROSTAGLANDIN INDUCED EMBRYONIC/FETAL MORTALITY. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2003. v. 54. p. 254-256. Interpretive Summary: The return interval to estrus, synchrony and fertility of the return estrus following PGF induced termination of pregnancy was similar or greater than that of cows in the luteal phase of their estrous cycle. Cows that experience early pregnancy losses during a breeding season likely exhibit a fertile estrus soon afterwards preventing low overall breeding season pregnancy rates from being realized in beef cow herds.
Technical Abstract: Late embryonic mortality occurs in approximately 10% of beef cattle. The objective of this study was to evaluate the distribution and fertility of estrus following early pregnancy loss in beef cattle. Pregnant cows (n = 124) and non-pregnant cows (control; n = 173) were divided across 2 yr to receive PGF (25 mg, i.m.) at d 25 (PG25; n = 40), 30 (PG30; n = 43), or 35 (PG35; n = 41) of gestation or during the mid-luteal phase of their estrous cycle (controls). Control cows were further divided into three approximately equal groups to receive PGF on the same dates as PG25, PG30, and PG35 cows. All cows were placed with fertile bulls immediately after PGF and were observed for estrus twice daily for 45 (PG25 and 60 control cows), 40 (PG30 and 56 control cows), or 35 d (PG35 and 56 control cows). Pregnancy was confirmed among PG25, PG30, and PG35 cows by ultrasonography and detection of a fetal heartbeat at the time of PGF (d 0). Synchronization rate (5-d) was greater (P < 0.05) in yr 2 (87%) than yr 1 (77%), and greater (P < 0.05) for PG35 (98%) and PG30 (91%) cows than control (78%) or PG25 (72%) cows. The interval from PGF to estrus was 4.0 +/- 0.2, 4.6 +/- 0.4, 4.1 +/- 0.4, and 3.3 +/- 0.4 d for control, PG25, PG30, and PG35 cows, respectively (P > 0.10). Synchronized pregnancy rates were higher (P < 0.05) for PG30 (66%) and PG35 (68%) cows than for PG25 (40%) cows. Synchronized pregnancy rates of control cows (54%) were not different (P >/= 0.10) than previously pregnant cows. Breeding season pregnancy rates (yr 1) were lower (P < 0.05) for control cows (84%) than for PG35 (100%) cows, but not different (P > 0.10) than pregnancy rates of PG25 (95%) or PG30 (95%) cows. In summary, cows that received PGF early during gestation exhibited an estrus of normal fertility within 5 d. Cows that experience early pregnancy losses during a breeding season likely exhibit a fertile estrus soon afterwards to prevent low overall breeding season pregnancy rates from being realized in beef cow herds.