02347naa a2200205 a 450000100080000000500110000800800410001910000210006024501140008126000090019552017230020465000190192765000280194665300250197470000220199970000180202170000210203970000170206077300640207721523962023-03-15       2022    bl uuuu     u00u1 u    #d1 aTOMAZI FILHO, J.  aEffect of calving to timed artificial insemination interval on fertility of beef cows.h[electronic resource]  c2022  aThe objectives of this study were to determine the effect of calving to timed artificial insemination (C-TAI) interval on fertility of Bos taurus and Bos indicus cows and to determine the best C-TAI interval to include postpartum cows in TAI programs in each genotype (B. taurus and B. indicus). In experiment 1, a retrospective study was per-formed, with data from 2,709 TAI in Bos taurus and Bos indicus cows with different C- TAI intervals. There was a positive linear effect of C-TAI interval on the pregnancy probability (p&lt .0001). However, there was no effect or interaction with the geno-type. When C-TAI intervals were grouped in classes, pregnancy rate differed in groups (p&lt .05). Receiver operating characteristic (ROC) analysis was performed, and it was observed that 52 days would be the better C-TAI interval to maximize fertility in beef cows. According to the previous result, we further stratified into two C-TAI interval groups (≤ 52 days or &gt 52 days). Cows with C-TAI longer than 52 days (C-TAI &gt 52) had greater pregnancy rate (56%) than cows with short C-TAI (46%; p&lt .01). In experi-ment 2, 18 postpartum beef cows were subjected to TAI protocol at different C-TAI intervals (n= 6 cows per group): 40, 60 or 80 days postpartum. Cows with 60 days of C- TAI had a greater preovulatory follicle diameter than cows with 80 days postpartum (p&lt .05). The C-TAI interval did not affect (p&gt .05) the ovulation rate nor the propor-tion of endometrial polymorphonuclear leucocytes. We conclude that C-TAI interval affects pregnancy rate in both Bos taurus and Bos indicus. We recommend a C-TAI in-terval longer than 52 days to increase fertility of beef cows included in TAI programs.  aPregnancy rate  aReproductive efficiency  aEndometrial cytology1 aPFEIFER, L. F. M.1 aHOEFLE, C. A.1 aRODRIGUES, M. F.1 aFERREIRA, R.  tReproduction in Domestic Animalsgv. 57, p. 936?942., 2022.