Journal of Applied Animal Research

To compare two short protocols for synchronization of estrus and timed-artificial insemination (TAI), 79 pluriparous non-pregnant Holstein cows with active corpus luteum (CL) were selected from a commercial dairy farm in northern Mexico and allotted to one of two treatments in a completely randomised design. Group 1 cows (n= 39) received an injection of 15 mg PGF_2α, and 24 h later received 1 mg estradiol cypionate (ECP). Two days later cows were inseminated by appointment. Cows in group 2 received an injection of 100 μg GnRH 48 h after the PGF_2α injection and underwent a timed AI at 16–20 h after the GnRH injection. At the moment of CL diagnosis, blood samples were collected from all cows and analyzed for progesterone, to corroborate CL diagnosis. Pregnancy rates of cows in estrus were similar for both treatment groups with similar percentage of cows displaying intense estrus. The present study showed that estrus of lactating dairy cows can be successfully synchronized with short synchronization protocols using either GnRH or ECP, although the inaccuracy of rectal palpation for determining the presence of a functional corpus luteum lead to lower pregnancy rates than those attained with traditional protocol currently available to dairy producers.