Evaluation of efficacy of selected estrous synchronization programs depending on the functional state of the ovaries, heifers and cows of meat breed

Abstract

The objective of this study was to assess the effect of progesterone concentration (P4) and ovarian structure models before initiation of different synchronization programmes on pregnancy outcomes per artificial insemination (AI) (P/AI) in beef cattle. Cattle were randomly assigned to one of three different synchronization programes (8-d PRID+7PGF&TAI, PGF 7-d Select Synch+PRID&TAI and 7-d PRID+6PGF&TAI); blood sampling and ultrasound examinations were performed before (day .7) and at initiation (day 0) of synchronizations, and during the experiment. The models were designed based on the turnover in P4 and ovarian structures at day .7 and day 0: Groups of Model 1 were based on P4 (<1, 1-3.99 and ≥4 ng/ml); groups of Model 2 were based on P4 (<1 and ≥1 ng/ml) and referred to the phase of the oestrus cycle; groups of Model 3 were based on follicle (F) diameter (absent, <10 and ≥10 mm); groups of Model 4 were based on corpus luteum (CL) diameter (absent, <10,10.20 and ≥21 mm). It was indicated that P/AI for heifers and cows were 54.6and 55.3% in the 1st, 61.5 and 60.6% in the 2nd and 36.1% (only cows) in the 3rdsynchronizations (P < 0.05), respectively. Significant effect on P/AI of Model 1 in the LH, HL, HM, HH groups (P < 0.05) was found in 2nd and of Model 4 in MA, MM, HH, LA in 1st (P < 0.05) synchronizations. So, the presence of higher P4concentration (Model 1) and CL (Model 4) before initiation of synchronizations improves P/AI in beef cattle.