Effects of eCG in Milking Dairy Cows with High Levels of BUN and Synchronized with Ovsynch Protocol By Farshid Karami Previous research indicated that high blood urea nitrogen (BUN) concentrations are associated with decreased fertility in lactating dairy cows. This study was conducted to evaluate the effects of equine chorionic gonadotropin (eCG) administration (with or without eCG) on fertility of lactating dairy cows with different levels of BUN subjected to fixed-time artificial insemination (FTAI). Ovulation was synchronized in all cows using Presynch-Ovsynch protocol and started 37 days post parturition (pp). Blood samples were collected on days 36-38 and 50-55 pp to assess BUN and cows were classified as with high urea when BUN was >20 mg/dl(n=63); otherwise, they were classified as cows with optimal urea when BUN was >10 and < 15 (n=62). Within each group, cows were assigned randomly to receive either 600 IU eCG concurrent with PGF2α treatment of the Ovsynch protocol (treatment cows) or with no further treatment (control cows). Blood samples were collected on Days 0 and 5 after FTAI to evaluate the effect of eCG administration on synchornization and plasma concentration of P4. Pregnancy diagnoses were performed by ultrasound. No treatment effects were detected for pregnancy per AI at days 30±2. However, P/AI at Days 30 was not affected by treatment with eCG but P/AI at 60±2 days post-AI in cows with high BUN levels in control group was significantly less than treatment group with optimal BUN (OR=0.212; P=0.016). This significant difference of P/AI at 60 days post-AI was not observed in cows with high BUN treated with eCG. P4 concentrations on Days 5 was significantly different between treatments and control cows in both levels of BUN concentration. In this experiment, inclusion of eCG in ovsynch protocol increased progestrone concentrations in early luteal phase and improved reproductive efficiency in dairy cows with high levels of BUN. Key words: eCG, High BUN, Dairy Holsteins, Presynch/Ovsynch

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