Effect of Using Progesterone Releasing Intravaginal Device with Ovsynch Program on Reproduction in Dairy Cattle during Summer Season

Sixty postpartum lactating Friesian cows in 3 treatments at a commercial dairy farm were used to study the effect of using progesterone supplementation with GnRH and PGF2$\alpha$ synchronization with and without timed AI on fertility during summer. Cows in treatment1($Tr_1$) and treatment2 ($Tr_1$) were fitted with progesterone releasing intravaginal device (PRID) device and injected with 10 g GnRH agonist on $51{\pm}3$ d postpartum (pp). Seven days later, PRID was removed and cows received 25 mg PGF2$\alpha$. Two days later, $Tr_1$ cows received another injection of 10 g GnRH and timed AI 16-20 h later. Control cows received only 25 mg PGF2$\alpha$ $58{\pm}3d\;pp$. $Tr_2$ and control cows were AI at detected estrus. Serum progesterone for all cows was determined on days of injection, AI and 21, 23 and 28 d postinsemination. Pregnancy rates from first AI based on serum P4 concentrations on d 21, 23 and 28 postinsemination (50, 40 and 35%) and that based on rectal palpation 40-45 d postinsemination (30, 15 and 15% for $Tr_1$, $Tr_2$ and control cows, respectively) did not differ among the three groups. Whereas, pregnancy rate at 120 d pp for $Tr_1$ (65%) was higher (p