Economics of resynchronization strategies including chemical tests to identify nonpregnant cows

Our objectives were to assess (1) the economic value of decreasing the interval between timed artificial insemination (TAI) services when using a pregnancy test that allows earlier identification of nonpregnant cows; and (2) the effect of pregnancy loss and inaccuracy of a chemical test (CT) on the economic value of a pregnancy test for dairy farms. Simulation experiments were performed using a spreadsheet-based decision support tool. In experiment 1, we assessed the effect of changing the interbreeding interval (IBI) for cows receiving TAI on the value of reproductive programs by simulating a 1,000-cow dairy herd using a combination of detection of estrus (30 to 80% of cows detected in estrus) and TAI. The IBI was incremented by 7 d from 28 to 56 d to reflect intervals either observed (35 to 56 d) or potentially observed (28 d) in dairy operations. In experiment 2, we evaluated the effect of accuracy of the CT and additional pregnancy loss due to earlier testing on the value of reproductive programs. The first scenario compared the use of a CT 31 +/- 3 d after a previous AI with rectal palpation (RP) 39 +/- 3 d after AI. The second scenario used a CT 24 +/- 3 d after AI or transrectal ultrasound (TU) 32 d after AI. Parameters evaluated included sensitivity (Se), specificity (Sp), questionable diagnosis (Qd), cost of the CT, and expected pregnancy loss. Sensitivity analysis was performed for all possible combinations of parameter values to determine their relative importance on the value of the CT. In experiment 1, programs with a shorter IBI had greater economic net returns at all levels of detection of estrus, and use of chemical tests available on the market today might be beneficial compared with RP. In experiment 2, the economic value of programs using a CT could be either greater or less than that of RP and TU, depending on the value for each of the parameters related to the CT evaluated. The value of the program using the CT was affected (in order) by (1) Se, (2) Sp, (3) pregnancy loss, (4) proportion of Qd, (5) percentage of cows AI in estrus, and (6) cost of CT. A change of 1% in the Se of the CT was 1.8 times more important than a similar change in Sp or pregnancy loss, and 13.7, 55.0, and 305.8 times more important than similar changes in Qd, cows inseminated in estrus, and cost of CT. We conclude that the major effect of using a CT is the potential of decreasing the IBI. Moreover, inaccuracy of the CT and additional pregnancy loss due to earlier testing resulted in smaller economic differences than when using RP or TU 8 d later.