The use of fixed-time artificial insemination and resynchronization of second estrus in beef cattle
The objective of this study was to evaluate the effectiveness of four fixed-time artificial insemination (FTAI) synchronization programs in beef cattle. In Trial 1, cattle (n = 225) were randomly assigned to one of two FTAI programs (5X and 4X). On Day 0, cattle received a CIDR-B, 1 mg of estradiol benzoate (EB) and 100 mg of progesterone. On Day 6, the 5X group received 25 mg of PGF2[alpha]. On Day 7, CIDR-B's were removed and the 4X group received 25 mg PGF2[alpha]. On Day 8, cattle received 1 mg of EB and on Day 9 were inseminated. Conception rates (CR's) were 69% (81/116) for 5X and 66% (72/109) for 4X (p > 0.05). In Trial 2, cattle (n = 202) received the 4X or the 3X system which replaced EB with 100 [mu]g of gonadorelin (GnRH) on Days 0 and 9 concurrent with insemination. Conception rates were 64% (65/102) for 4X and 63% (63/100) for 3X (p > 0.05). In Trial 3, cattle (n = 196) received the 3X and PRE-CIDR system. Cattle in the PRE-CIDR system received a CIDR-B on Day 12. CIDR-B's were removed on Day 0 and all cattle received GnRH. On Day 7, cattle received PGF2[alpha]. On Day 9, cattle received GnRH concurrent with insemination. Conception rates were 54% (54/99) for the 4X and 60% (58/97) for the PRE-CIDR (p > 0.05). In Trials 2 and 3, a once used CIDR-B was inserted from days 12 to 19 after FTAI and cattle were inseminated following observed estrus after CIDR-B removal. The resynchronization program CR were 68% (39/57) for Trial 2 and 75% (36/48) for Trial 3 (p > 0.05). In Trial 4, cattle (n = 201) received the 4X and 3X systems. Following FTAI half of cattle received a used CIDR-B from days 15 to 22 and the control group received no further treatment. Cattle were inseminated following observed estrus. Conception rates to FTAI were 70% (71/101) for the 4X and 66% (66/100) for the 3X (p > 0.05). The resynchronization program CR were 78% (18/24) for the CIDR-B group and 45% (10/22) for the control group (p = 0.07). In conclusion, the use of PGF2[alpha] on Day 6 or 7 did not affect CR's. Conception rates for the EB or GnRH groups were not different. The resynchronization results indicate that is possible to re-use the CIDR-B to synchronize the second estrus in cattle not pregnant to FTAI. Finally, reducing cattle handling from five to three times did not significantly affect CR to FTAI.