Influence of IBR vaccination timing on ovarian and uterine statuses and circulating progesterone and estradiol 17β in synchronized crossbreed heifers

To declare the interaction between IBR vaccination and the synchronization protocol, dairy heifers (n= 24), 12.5-14.0 months old, were equally and randomly assigned according to the timing of vaccination into pre-synch group (vaccinated 3 days before synchronization), in-synch group (vaccinated five days after the start of the synchronization), and control (given sterile water same as treated groups). Ovarian and uterine ultrasound examinations were done on Day -3, 5, 8, 19 and 43. Blood samples were collected for measuring estradiol and progesterone levels after vaccination. The effect of IBR vaccination on ovarian activity appeared on Day 5 (P= 0.07) through decrease in the mean diameter of the growing follicles in pre-synch group compared to in-synch group, and on Day 8 through reduction of the total and growing follicular numbers (P= 0.05 and 0.03, respectively) in in-synch group compared to other groups. Estradiol levels were significantly (P=0.03) higher on day 8 (day of insemination) in the pre-synch group than the other groups. The uterine changes were characterized by a significant decrease in uterine diameters on Day 5 in the pre-synch group compared with control. The ventral uterine diameter in-synch group decreased on Day 5 (P= 0.015) and re-increased on Day 8 (P= 0.007 compared to control group. In conclusion, administration of IBR vaccination prior to synchronization may possess some impacts on the ovarian and uterine activities without major adverse reactions on reproduction. Therefore, vaccination timing is recommended to be at least three days away from the beginning of the synchronization protocol.