Comparison of two intravaginal progesterone-releasing devices in lactating Holstein cows synchronized with a 5-d GnRH-based timed-AI protocol

The objective of the study was to compare the effectiveness of CIDR vs. PRID-Delta devices for use in a 5-day Ovsynch protocol for TAI in lactating Holstein cows that were either not in estrus after the end of the voluntary waiting period or non-pregnant and not returning to estrus following the previous AI. Cows fitted with a collar-mounted automated activity monitoring system (Alta Cow Watch) were subjected to a standard 5-d Ovsynch protocol [100 mu g of gonadorelin (GnRH) on Day 0 and 500 mu g of cloprostenol on Days 5 and 6] and allocated randomly to receive either an intravaginal device containing 1.35 g (CIDR; n = 304) or 1.55 g (PRID (R) DELTA; n = 304) of progesterone between Day 0 and 5. All cows received a second administration of GnRH at approximately 56 h and timed-AI (TAI) 72 h after intravaginal device removal. Inseminations were done using conventional frozen-thawed semen. Estrus events prior to TAI were recorded and transrectal ultrasonography was done on Day 0 to determine presence of a corpus luteum (CL) and 33 and 61 d post-TAI, respectively, to diagnose and confirm pregnancy. Cows had an average of 2.2 lactations, 124.3 days in milk, and a milk yield of 43.6 kg/d at enrollment. The overall percentage of cows with a CL at initiation of treatment was 68.8 % and did not differ between treatment groups. Cows with a CL had greater pregnancy per AI (P/AI) at 33 and 61 d post-TAI than cows without a CL (P < 0.01; 46.9 and 42.3 % vs. 32.1 and 27.4 %, respectively). The overall percentage of cows that expressed estrus prior to TAI was 24.8 % and did not differ between treatment groups; however, estrus expression prior to TAI affected P/AI at 33 and 61 d post-TAI (P < 0.01; 53.6 and 49.0 % vs. 38.5 and 33.9 % for those expressing or not expressing estrus, respectively). Pregnancy per AI at 33 d post-TAI tended to differ between treatment groups (P = 0.08; 46.1 vs. 38.5 % for PRID and CIDR groups, respectively) and P/AI at 61 d post-TAI was greater (P < 0.01) for PRID-treated cows (43.8 %) compared to CIDR-treated cows (31.6 %). Thus, PRID-treated cows had lower pregnancy loss than CIDR-treated cows (P < 0.01; 5.0 vs. 17.9 %). Also, treatment with a PRID tended (P = 0.08) to result in fewer twin pregnancies (7.9 vs. 14.5 % for PRID and CIDR treated cows, respectively). In conclusion, lactating dairy cows subjected to a 5-d Ovsynch TAI protocol plus a PRID-Delta had greater P/AI at 61 d post-TAI, lower pregnancy loss between 33 and 61 d post-TAI, and fewer twin pregnancies compared to cows subjected to a 5-d Ovsynch protocol plus a CIDR.