Fertility Response of Cyclic and Acyclic High Lactating Holstein Dairy Cows to PRID-Modified Ovsync Protocol

Objective: This study aimed to evaluate the fertility response and concurrent follicular dynamics and hormonal profiles of cyclic and acyclic high lactating Holstein cows to PRID Modified (PRID-synch) protocol in comparison with Basic-Ovsynch protocol (control). Methods: Forty cyclic and forty acyclic cows were subjected to modified PRID-sync and Basic-Ovysynch (control) protocols. The cows subjected to the modified PRID-synch included 20 out of cyclic cows (cPRID-synch) and 20 out of acyclic cows (acPRID-synch). Similarly, the cows subjected to Basic-ovsync included 20 out of the cyclic cows (cBasic-ovsynch) and 20 out of the acyclic cows (acBasich-ovsynch). The fertility response and concurrent follicular dynamics, circulating levels of progesterone (on Days 0, 3, and 5), E2, and insulin (on Days 7, 8, 9, and 10) were evaluated. Results: In cyclic cows, the conception rate was numerically higher in cPRID-synch than cBasic-ovsynch (50% versus 30%). The conception rate did not differ between acPRID-synch and acBasic-ovsynch (30% versus 20%) in acyclic cows. The largest follicle diameter (LFD) was greater (P<0.05) in cBasic-Ovsynch than cPRID-synch on Days 7, 8, and 9 but did not differ between the two groups on Day10. The LFD did not differ (P>0.05) between acPRID-synch and acBasic-Ovsynch on Days 9 and 10 but, on Days7 and 8, it was greater (P<0.05) in acBasic-Ovsynch than acPRID-synch. Conclusion: It could be concluded that supplementation of P4 via PRID insertion, on Days 0-7 in the ovsynch protocol in cyclic or acyclic cows improves fertility response with higher response in cyclic cows than acyclic cows.