Effect of delaying time of AI based on Estrotect patch status on pregnancy rates of beef heifers and nursing beef cows

Abstract

Four studies were conducted to evaluate the efficacy of a delayed timed AI (TAI) protocol. The objective was to evaluate the use of Estrotect patch status to determine optimum TAI implementation. Experiment 1 was conducted with, 997 cows across 6 locations were administered a 7-d CO-Synch + controlled internal drug release (CIDR) estrous synchronization protocol. The experimental design was a 2 x 2 factorial; factors were patch status at 58 h post PGF2α injection (activated or inactivated) and time interval from PGF2α to TAI (58 or 76 h). Patch status was characterized at 58 h post PGF2α into 4 scores: 1 = 0% activated, 2 = 50% activated, 3 = 100% activated, and 4 = missing. Females with a patch status of 3 were considered to be activated and females with patch status of a 1 or 2 were considered to be not activated. Females with missing patches were removed. There was no treatment x location interaction for pregnancy rate (P = 0.96), so data were pooled across locations. There was a tendency (P = 0.07) for an interaction between the main effects for pregnancy rate. Pregnancy rate was greater (P < 0.01) in cows with activated patches at 58 h post PGF2α (67.0%) compared to those with inactivated patches (51.1%). There was no difference (P = 0.99) for pregnancy rate when comparing the 58 (59.9%) vs. 76 h PGF2α to TAI interval (58.7%). Pregnancy rates for cows with a patch status of 3 at 58 h post PGF2α were greater (P < 0.05) than cows with a patch status of 1 or 4 and tended (P = 0.09) to be greater than cows with a patch status of 2. Cows with a patch status of 1 tended (P = 0.06) to have increased pregnancy rates by delaying TAI to 76 h post PGF2α. Although, it was not different (P = 0.13), there was a 7.4 percentage point increase in pregnancy rates for cows with inactivated patches that received TAI at 76 vs. 58 h. Experiment 2 was conducted to evaluate delayed TAI on 1,682 heifers across 3 locations. The objective was to evaluate the use of Estrotect patch status at various recommended and delayed insemination times for a TAI protocol. Experiment 2a was implemented with 1,159 Bos taurus heifers synchronized using a 14 d melengestrol acetate (MGA) – PGF2α protocol. Estrotect patches were applied at the time of PGF2α injection and evaluated at the time of insemination. Heifers were subsequently assigned to 5 treatments: 1) recommended 72 h post PGF2α TAI with activated patches, 2) recommended 72 h post PGF2α TAI with inactivated patches, 3) 12 h delayed TAI with inactivated patches, 4)18 h delayed TAI with inactivated patches, and 5) heifers with missing patches. Experiment 2b was conducted with 449 Bos taurus heifers synchronized using a 14 d MGA – PGF2α protocol. Heifers were divided into 3 treatments: 1) recommended 72 h post PGF2α TAI with activated patches, 2) recommended 72 h post PGF2α TAI with inactivated patches, and 3) an 8 h delayed TAI with inactivated patches. Experiment 2c utilized 74 heifers synchronized with a 7-d CO-Synch plus CIDR protocol. All heifers had Estrotect patches applied at the time of CIDR removal and PGF2α injection. Patch status was evaluated 58 h post PGF2α injection on all heifers. This experiment was analyzed as a 2 x 2 factorial with patch status 58 h post PGF2α injection (activated or inactivated) and at the time of insemination (58 or 76 h). In experiment 2a, differences (P < 0.05) in pregnancy rates were different by patch status across treatments. Similarly, experiment 2b demonstrated resulted in differences (P < 0.05) in pregnancy rates when comparing the activated patch treatment to both the inactivated patch treatment and the delayed inactivated treatment. However, no differences (P > 0.05) were seen in either experiment 2a or 2b when comparing the recommended inactivated patch treatments to any of the delayed inactivated patch treatments regardless of delay interval. Experiment 2c demonstrated a tendency (P = 0.07) for the interaction pregnancy rates to be increased when activated patches at 58 h were inseminated at 58 h post PGF2α injection and when inactivated patches at 58 h were inseminated at 76 h post PGF2α. Pregnancy rates for the main effects of patch status (P > 0.05) and interval inseminated (P > 0.05) did not differ. Results show a definitive increase in pregnancy rates when comparing heifers with activated patches to heifers with inactivated patches. However, delaying insemination time of heifers with inactivated patches did not increase pregnancy rates.