292 Tandem Administration of Prostaglandin F2α and Gonadotropin-Releasing Hormone in Beef Heifers and Cows as a Convergent Presynchronization Method in the 7 & 7 Synch Protocol

An experiment was designed to evaluate modifications to the 7 & 7 synch protocol with the hypothesis that tandem administration of prostaglandin F2α (PG) and gonadotropin-releasing hormone (GnRH) during the presynchronization portion of the protocol would generate a convergent ovarian response among anestrous and estrous cycling females. Nulliparous (n = 153), primiparous (n = 92), and multiparous (n = 413) Angus-cross females across four locations were blocked based on parity and pre-treatment cyclicity status (presence or absence of a corpus luteum) as assessed via transrectal ovarian ultrasonography. Within block, females were randomly assigned to one of three treatments. Females assigned to the 7 & 7 Synch treatment received an intravaginal progesterone-releasing insert (CIDR) and administration of PG on day 0, administration of GnRH on day 7, and administration of PG coincident with CIDR removal on day 14. Females assigned to 7 & 7 Synch + G received the same treatment schedule with the modification that GnRH was administered in tandem with the PG on day 0. Females assigned to 7 & 7 Synch + G + P received GnRH in tandem with PG on both day 0 and day 7 of the treatment schedule. Fixed-time artificial insemination (FTAI) was performed at 54 h after CIDR removal for nulliparous females and at 66 h for primiparous and multiparous females. Transrectal ovarian ultrasonography was performed on day 7 and day 14 to characterize the largest follicle diameter (LFD) as well as the presence/absence and number of corpora lutea (CL). Expression of estrus before FTAI was characterized in three locations using estrus detection patches (Estrotect. Approximately 75 to 90 days after FTAI, pregnancy status was determined via transrectal ultrasonography. Day 7 CL status was affected by treatment (P = 0.002), with a greater proportion of females presenting with CL on Day 7 when treated with the modified treatments (64%) as compared with the 7 & 7 Synch treatment (31%). Day 14 LFD was affected by treatment (P = 0.002), with a larger average LFD among females treated with 7 & 7 Synch + G + P (12.0 mm) as compared with 7 & 7 Synch (11.4 mm) or 7 & 7 + G (10.7 mm). Pregnancy rate to FTAI was affected by pre-treatment cyclicity status (P < 0.0001) and semen type (P = 0.0003) and tended to be affected by treatment (P = 0.09) with 7 & 7 Synch + G + P tending to result in a greater proportion pregnant (58.86%) as compared with 7 & 7 Synch (49.17%) and 7 & 7 Synch + G (48.79%). Tandem administration of GnRH and PG on days 0 and 7 of the 7 & 7 Synch protocol effectively generated a convergent ovarian response among anestrous and estrous cycling beef females and tended to result in increased pregnancy rates to FTAI.