The Effect of Comfort- and Hot-Period on the Blood Flow of Corpus Luteum (CL) in Cows Treated by an OvSynch Protocol

SIMPLE SUMMARY: Doppler ultrasonography is frequently used to measure blood flow. The Ovsynch program is applied to synchronize the timing of ovulation in dairy cows. Heat stress can negatively affect the hormonal balance, ovarian activity, and blood flow. In this study, the effect of heat stress on corpus luteum blood flow, progesterone, and insulin-like growth factor parameters was investigated during and after Ovsynch synchronization. Our results showed that synchronization initiated with high progesterone values caused significantly higher blood flow and greater corpus luteum area in the comfort period when compared with the hot period. In addition, insulin-like growth factor values were found significantly higher during the comfort period compared to heat stress. Under heat stress circumstances, the Ovsynch synchronization provided better results when the progesterone levels were high. We suggest that it may be better to apply the modified Ovsynch program to increase progesterone levels in cows with low progesterone values when the protocol is initiated during the heat stress period. ABSTRACT: The values of luteal blood flow (LBF), total corpus luteum (CL) area (TAR), and progesterone (P4), during and after OvSynch (OvS) protocol in comfort (CP; n = 40) and hot periods (HP; n = 40) were compared. We investigated how low and high P4 values obtained before the application affected the parameters above during CP and HP periods. Blood samples were collected before the OvS application on day 0 (OVSd0), day 9 (OeG), and day 18 (9th day after OeG: OvSd9). The P4 (ng/mL) values of the animals exhibiting dominant follicles were between 0.12–0.82 in HC and 0.1–0.88 in CP (P4-2: 4.36–4.38 and P4-3: ≥7.36 ng/mL). The LBF values were measured on days 7 (OvSd7) and 9 (OvSd9) after the OeG. The P4 mean values at day 0 (OvSd0) were classified as low (P4-1), medium (P4-2), and high (P4-3). The LBF and the TAR values in the P4-2 and P4-3 on OeG day 9 were higher than in HP (p < 0.05; 0.001), but there was no significant difference in the P4-1. In conclusion, when the OvS program was initiated with low P4 values, no difference was observed between HP and CP in terms of LBF values; however, when the program was started with high P4 values, there were significant increases in LBF and TAR values in the CP compared to the HP.