A Reduced Drug and Labor Timed Artificial Insemination Protocol for Lactating Dairy Cows: Evaluation of the 12-day PRID-DELTA Program

The present study examined a modified, low-drug timed artificial insemination protocol using PRID-DELTA (PRID), an intravaginal progesterone-releasing device with an estradiol benzoate (EB) capsule. The key modification was the omission of concomitant prostaglandin F2α (PG) administration, aimed at reducing drug use and labor. In 178 lactating cows confirmed to be clinically healthy (absence of endometritis or ovarian cysts) and exhibiting echogenic structures in the ovary via transrectal ultrasonography, PRID was inserted for 12 days (Days 0–12). Ovulation was induced with 1 mg EB on Day 13. We assessed the timing of ovulation and the incidence and function of a persistent corpus luteum (CL). Fertility outcomes with and without the PG co-administration were compared using a contingency table and multivariate logistic regression analyses. The ovulation induction rate reached 86%, with an ovulation synchronization rate (ovulation within 48 h of EB administration) of 81%. A persistent functional CL was detected in 11.8% of cows on Day 14. Although the presence of a persistent functional CL was associated with a lower conception rate, the omission of PG at PRID removal did not significantly impact the overall conception rate. In conclusion, despite the 11.8% incidence of a persistent functional CL, the omission of PG was not detrimental to the overall conception rate. Therefore, this 12-day PRID protocol without PG is a feasible and effective alternative that successfully reduces drug usage and labor while maintaining reproductive performance.