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<0.05) than that in $Tr_2$ (30%) or control (30%). The overall pregnancy rate was not significantly different (90, 90 and 75% for $Tr_1$, $Tr_2$ and control, respectively). Days open for cows in $Tr_1$ ($100.3{\pm}9$) was less (p<0.03) than that in $Tr_2$ ($130.9{\pm}9$) or control ($135.1{\pm}10$). Results indicate that using PRID device with Ovsynch program had significantly increased pregnancy rate and decreased days open compared to AI at detected estrus after synchronization with GnRH, PRID and PGF2$\alpha$ or synchronization with one injection of PGF2$\alpha$.