Synchronized ovulation for first insemination improves reproductive performance and reduces cost per pregnancy in dairy heifers

The objectives were to evaluate the effects of synchronizing estrus and ovulation to implement a timed artificial insemination (AI) at first insemination on reproductive performance and cost per pregnancy in dairy heifers. Six hundred eleven Holsteins heifers at approximately 400 d of age from 3 farms were enrolled in the study. Six days before moving to the breeding pens, heifers were allocated randomly to AI after detected estrus from study d 0 to 84 (CON, n=306), or to timed AI for first AI followed by detected estrus for the remainder of the 84-d study (TAI, n=305). Heifers receiving TAI were enrolled in the 5-d timed AI protocol on study d -6 (d -6, GnRH and a progesterone insert; d -1, PGF2α and insert removal; d 0, PGF2α; d 2, GnRH + AI), and they were allowed to be bred the day before scheduled timed AI if detected in estrus. Starting on study d 0, estrus was detected daily. Heifers in estrus were inseminated on the same morning as detected estrus. Control heifers not inseminated by study d 7 received PGF2α and this treatment was repeated every 2 wk until AI. The study lasted 84 d to allow a period of breeding equivalent to four 21-d estrous cycles. A herd budget accounting for inputs for both treatments was created to determine the cost per pregnancy. Sensitivity analysis compared economic differences between the 2 treatments under different input scenarios when detection of estrus after the first AI varied from 50 to 80%. Interval to first AI was 8 d shorter for TAI than for CON. Pregnancy at first AI did not differ between treatments (CON=58. 3 vs. TAI=62. 8%). In contrast, TAI increased pregnancy per AI (P/AI) compared with CON in heifers inseminated with sex-sorted semen (CON=31. 6 vs. TAI=54. 8%). The 21-d cycle insemination rate was greater for TAI (91. 4%) than for CON (82. 4%), even when evaluated after the first 21 d in the study (CON=68. 2 vs. TAI=77. 1%). The increased insemination rate improved the 21-d cycle pregnancy rate from 47. 9% in CON to 57. 2% in TAI heifers. In fact, the hazard of pregnancy was 60% greater for TAI than CON. The increased pregnancy rate in TAI reduced the median days to pregnancy by 12 d (CON=2. 0 vs. TAI=14. 0) and increased the proportion of pregnant heifers by 6. 3 percentage points by study d 84 (CON=85. 2 vs. TAI=91. 5%). The cost per pregnancy was 17. 00 less for TAI than CON. The sensitivity analysis indicated that TAI was economically more advantageous to produce a pregnancy compared with CON. Only when insemination rate after the first 21 d of breeding was very high and P/AI was relatively low did the cost per pregnancy become similar for the 2 treatments. Collectively, inseminating all heifers within 2 d of breeding with the 5-d timed AI protocol maintains P/AI, improves pregnancy rate, and reduces cost per pregnancy compared with insemination after detected estrus.