Resynchronization in dairy cows 13 days after TAI followed by pregnancy diagnosis based on corpus luteum vascularization by color doppler

Abstract

In the present study 2 experiments were performed aiming to evaluate the reproductive efficiency of dairy cows undergoing resynchronization 13 d (Day 13) after TAI (Exp 1) and the effect of the resynchronization on the synchronization of the new follicular wave emergence and on the CL activity (Exp 2). The Exp 1 enrolled 183 lactating cows (25.2±8.8 L milk/d) distributed into two groups: control (CON, n=93) and resynchronization (RES, n=90). On a random day of the estrous cycle, all animals were submitted to the same TAI protocol [2mg of estradiol benzoate (EB)+progesterone device (P4)-8d (device removal+1mg estradiol cypionate (EC)+0.150mg of cloprostenol (PGF2 α)-TAI 48 h later] . The females of the CON group were inseminated after detection of estrus between Days 18 and 25 after TAI. The cows of the RES group were resynchronized with the insertion of a P4 device (Primer®, Agener-Tecnopec) and 1.5mg of EB (RIC-BE®, Agener-Tecnopec) on Day 13. On Day 21 the P4 devices were removed. At the same time, the females from both experimental groups underwent a color Doppler ultrasonography in order to assess the vascularization of the CL. All animals of the RES group classified as nonpregnant based on the CL vascularization (CL area <3cm2, peripheral vascularization ≤25% and central with reduced signals) or absence of CL received 1mg of EC (ECP®, Zoetis), 0.150 mg PGF2α (Estron®, AgenerTecnopec) and were inseminated 48 h later. The pregnancy diagnosis of the 1st TAI was performed on Day 30 in all females. Statistical analysis was performed using the GLIMMIX procedure of SAS®. The vascularized CL rate on Day 21 (P=0.003) and pregnancy rate (PR) on Day 30 after the 1st TAI (P=0.02) were lower in the RES group (40.0%, 36/90 and 14.9%, 13/87) compared to the CON group (62.4%, 58/93 and 32.6%, 28/86; respectively). However, there was no difference (P=0.98) in the PR after the 2nd AI between the CON (25.0%, 3/12) and RES group (22.6%, 12/53). In Exp 2, 17 lactating cows were submitted to the same treatments described in Exp 1 (CON, n=9 and RES, n=8). All cows were submitted to ultrasound exams every 24 h and evaluated by Doppler every 48 h from Day 13 to 21. Statistical analysis was performed using the MIXED procedure of SAS. An interaction (P=0.07) between treatment and time was observed for the vascularization rate of the CLs. Although a new follicular wave emergence was induced 3.2 ± 1.4 d after EB treatment (RES group) and similar vascularization rate of the CLs was observed on Day 13 (CON: 87.8 and RES: 84.4%) and Day 15 (CON: 90.6 and RES: 86.9%); the vascularization of the CLs from animals of the RES group was reduced from Day 17 onwards (Day 17: 71.9, Day 19: 51.9 and Day 21: 40.6%) compared to the CON group (Day 17: 89.4, Day 19: 88.9 and Day 21: 76.1%). In conclusion, the resynchronization using 1.5 mg EB 13 d after the 1st TAI reduces the vascularization of the CL and consequently, the pregnancy rate to the 1st TAI in dairy cows.