Strategic use of estrus intensity to combine timed artificial insemination and embryo transfer in large-scale cattle reproduction programs

This study compared the reproductive performance of three different programs using conventional fixed-time artificial insemination (FTAI), fixed-time embryo transfer (FTET), and their combined use, considering estrus intensity as a criterion for the reproductive program. Brangus multiparous cows (n = 1.100), 40-50 days postpartum, 4-8 years old, and body condition scores 2.50 of 4.50 underwent a protocol for ovulation synchronization based on progesterone (P4) and estradiol on D0. On D10, one of three Programs I-III was implemented: control FTAI (n = 147 cows), control FTET (n = 617) with embryos from in vitro production (IVP) on D17, or FTAI + FTET (n = 336), where cows with low or no estrus expression were inseminated on D10, similar to Program I, while those with high-intensity expression received one embryo from IVP on D17, similar to Program II. Corpus luteum (CL) size and quality were assessed using B-mode and Doppler ultrasound on D17. The service/utilization rate was higher for FTAI and combined FTAI + FTET than for the conventional FTET. The program that used only FTAI resulted in higher pregnancy at 30 and 60 days, as well as lower pregnancy loss, compared to programs that used embryos. Furthermore, the FTAI + FTET program showed reduced pregnancy loss, compared to the FTET program. In the combined program, the CL was greater in those who received FTET alone than in those who received FTAI alone. A higher proportion of recipients with CL with a high luteal blood perfusion score was observed in the FTET group compared to the FTAI group. Satisfactory reproductive rates can be achieved using conventional FTAI or FTET programs. However, the combined program, associated with monitoring the intensity of estrus expression, is a promising strategy for allocating females with absent or low estrus expression to FTAI, and those with high estrus intensity to FTET. Recipients with high-intensity expression had higher CL quality and, when transferred, maintained satisfactory reproductive performance compared with conventional FTET.