Effect of progesterone administration after TAI on the conceptus development and the pregnancy rate in lactating buffaloes

It was aim with this study increase the conceptus length and the pregnancy rate in lactating buffaloes through the P4 administration 3 or 6 days after TAI. For this, three experiments were performed. In the exp.1, the pattern of P4 release was measured on 8 ovariectomized buffaloes (crossover design) that received 300 or 600 mg (P300 or P600 group, respectively) of injectable P4 (iP4; Sincrogest Injetavel ®, Ourofino Agronegocio, Brazil). Blood samples were collected for the P4 dosages at -24, 0, 6, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216 and 240 h after iP4 administration. In the exp.2, 24 buffaloes were subjected to the Ovsynch protocol (D0, GnRH; D7, PGF2α; D9, GnRH; D10, IATF) and evaluated by ultrasonography (Mindray DP2200Vet, China) in D13, when the females with CL presence were distributed into 3 groups: control (C, n = 8); P4D13 (n = 8; 300mg of iP4 in D13); P4D16 (n = 8; 300mg of iP4 in D16). In D26, the buffaloes were slaughtered, the genitals was removed and were measured the CL diameter (CLDs) and the CL weight (CLW) and the conceptus presence (CP) and the conceptus length (CoLe). Stained slides of luteal and endometrial tissue were examined by optical microscopy to determine the % of small and large luteal cells (SLC and LLC) and the number (GEn), area (AGEn) and perimeter (PGEn) of endometrial glands. In the exp.3, 337 buffaloes were subjected to the Ovsynch protocol and, as well as in the exp.2, the females with CL presence were divided into 3 groups (C, n = 89; P4D13, n = 92; P4D16, n = 93). The functionality (central vascularization - CV; and peripheral vascularization – PV; score 0-4) and the CL diameter (CLD) were evaluated in D17, D21 and D25 by ultrasonography in color Doppler mode (Mindray M5Vet; China). Furthermore, the pregnancy rates at the 30 (DG30) and 60 (DG60) days after TAI and pregnancy loss (PL; Mindray DP2200Vet) were evaluated. Data were analyzed using the GLIMMIX procedure of SAS®. The P4 levels were higher in P600 compared to P300 at all times after iP4 (Ptreat 0.05). In exp.3, there was interaction treatment*time for the CV, PV and CLD (P < 0.07). There was a reduction of the CV, PV and CLD in P4D13 compared to C and P4D16 group as the evaluation moments. There were no difference between C, P4D13 and P4D16 groups for the DG30 (56.8 vs. 46.4 vs. 61.2%; P = 0.13) and for the PL (0.0 vs. 10.3 vs. 5.8%; P = 0.73). However, there were reduced pregnancy rates in DG60 for the P4D13 compared to C and P4D16 (41.7 vs. 56.8 vs. 57.7%; P = 0.07). It was conclude that the treatment with 300mg of iP4 in D13 or D16 of Ovsynch protocol did not increase the conceptus length and the pregnancy rate in lactating buffaloes submitted to TAI. Furthermore, the treatment with P4i three days after TAI reduced the central and the peripheral CL vascularization, the CL diameter and the pregnancy rate.