138. Effects of a Bovine Appeasing Substance Applied at Estrous Synchronization on Stress, Cyclicity, and Pregnancy

Abstract Management practices and reproductive technologies can induce stress resulting in impaired reproductive performance. This study aimed to evaluate a bovine appeasing substance (BAS) applied at estrous synchronization and the impacts on reproductive stress, cyclicity, and pregnancy rates. Crossbred beef cows (n = 120) were stratified by body weight (BW), body condition score (BCS), and post-partum interval, then allocated to one of two treatments: 1) administered BAS topically to the nuchal skin (5 mL) and poll (5 mL) at estrous synchronization (BAS; n = 60), or 2) control where BAS was not administered (CON; n = 60) at estrous synchronization. Estrous synchronization and breeding protocols followed a 7-day-CO-Synch + CIDR combined with heat detection and timed artificial insemination (AI). On d 0 (synchronization initiation), 7, breeding (d 9 and 10), and 106, BW was recorded and change in BW was calculated. On d 0 and d 106, BCS was recorded. A subset (BAS, n = 40; CON, n = 40) were selected for blood collection for serum cortisol and progesterone concentrations. Cortisol was analyzed for all sample collection days while progesterone was analyzed on d 0 and d 9 or 10. Pregnancy was determined on d 106 via transrectal ultrasonography. Calving rate was calculated at the conclusion of calving season. Data were analyzed using the MIXED procedure of SAS for BW and BCS, and change in BW. Cortisol and progesterone were analyzed using the GLIMMIX procedure which included day and treatment by day interaction in the model. GENMOD was used for pregnancy. Significance was declared at P ≤ 0.05. Body weight was similar (P = 0.49) between BAS (870.92 kg) and CON (865.82 kg), additionally there were no differences over time (P = 0.80). Body condition between BAS and CON at the beginning of the study (4.45 and 4.47, respectively) and the conclusion (3.75 and 3.79, respectively) were similar (P ≥ 0.64).Stress was not reduced (P = 0.34) as indicated by cortisol concentrations between BAS (6.95 ng/mL) and CON (6.88 ng/mL) nor was there an interaction for treatment over time (P = 0.55). Similarly, progesterone concentrations did not differ (P = 0.15) between BAS (3.70 ng/mL) and CON (3.93 ng/mL) nor was there an interaction over time (P = 0.17). Overall pregnancy was not affected by treatment (P = 0.31), where pregnancy by AI represented 42.11% of overall pregnancy. However, pregnancy via AI differed (P < 0.01) where BAS pregnancy rates were lower compared to CON (25% and 75% respectively). The findings in this study suggest that applying BAS at estrous synchronization did not reduce stress at AI and did not improve reproductive success. Future studies should investigate BAS administration on heifers at estrous synchronization.