118 A comparison of intravaginal progesterone devices for fixed-time artificial insemination in beef cattle

Intravaginal progesterone (P4) devices used for ovarian synchronization before fixed-time AI (FTAI) differ in drug release, which may influence fertility outcome. A 2 × 2 study was designed to determine the effects of different intravaginal devices (PRID Delta, 1.55 g of P4 vs. CIDR, 1.38 g of P4) and parity (heifers vs. cows) on follicular dynamics, expression of oestrus, and pregnancy per AI (P/AI). At random stages of the oestrous cycle, nulliparous beef heifers and lactating cows were given 100 µg of gonadorelin (gonadotrophin-releasing hormone, GnRH) intramuscularly (IM) and assigned randomly to either the PRID (n = 76 heifers, 76 multiparous, 27 primiparous) or CIDR (n = 76 heifers, 73 multiparous, 32 primiparous) group. Devices were removed 5 days later, an oestrus-detection patch was applied just cranial to the tail head, and 500 µg of cloprostenol was given IM at the time of device removal and again 24 h later. At 72 h after device removal, cattle were inseminated and given 100 µg of GnRH IM. Transrectal ultrasonography was used to determine the diameter of the largest follicle on the day of device removal and at FTAI, ovulation time, and pregnancy status 30 days after FTAI. A colour change of ≥50% of the oestrus-detection patch at FTAI was taken as expression of oestrus. Data were compared among groups by 2-way ANOVA using MIXED and GLIMMIX procedures. There were no interactions between P4 device and parity for any endpoint. The diameter of the largest follicle (mean ± s.e.m.) was not different between PRID and CIDR groups on either the day of device removal (10.6 ± 0.1 vs. 10.9 ± 0.1 mm) or the day of FTAI (13.7 ± 0.1 vs. 13.9 ± 0.1 mm). The proportion displaying oestrus did not differ between P4 device groups, but was greater in heifers than in cows [121/152 (79.6%) vs. 135/207 (65.2%); P < 0.01], and the interval from FTAI to ovulation was shorter in heifers than in cows (27.8 ± 1.2 vs. 32.0 ± 1.1 h; P = 0.01). The P/AI was not different between P4 device groups or parity groups (overall 67.0%, 238/355). However, among lactating cows, the P/AI tended to be greater in the PRID vs. CIDR group [75/102 (73.5%) vs. 64/105 (61.0%); P = 0.10], and was greater in multiparous vs. primiparous cows [106/148 (71.6%) vs. 33/59 (55.9%); P = 0.04]. Among cattle that displayed oestrus, the P/AI tended to be greater in the PRID vs. CIDR group [92/123 (74.8%) vs. 85/131 (64.9%); P = 0.09]. Among lactating cows that displayed oestrus, the P/AI was greater in multiparous vs. primiparous cows [74/94 (78.2%) vs. 24/42 (57.1%); P < 0.01]. In summary, follicular dynamics and expression of oestrus did not differ between PRID and CIDR groups, but the P/AI tended to be greater in PRID-treated lactating cows and in cattle that displayed oestrus. This research was supported by CEVA Animal Health, Saskatchewan ADF, Agriculture and Agri-Foods Canada, and Rockway Inc.