12 A paradoxical response to different presentations of progesterone in buffaloes in fixed-time insemination programs

Owing to the difficulty of detecting estrus and the need for productive and reproductive management, fixed-timed AI (FTAI) has become a common practice in buffalo farming. It has been proposed that presynchronization of the ovarian status could improve pregnancy rates. Currently, a vaginal device impregnated with progesterone (P4) has been used to synchronize the emergence of follicular wave and ovulation, but it yields poorer results compared with those obtained in cattle. Recently, an injectable pharmaceutical form of P4 and estradiol (E2) has been developed for the same purpose. The aim of this study was to compare the effect of the use of different sources of P4 in an FTAI program. This study was conducted at the Pedro Antonio Silva Sons farm located in General Paz, Corrientes, Argentina at the end of the nonbreeding season during February 2024. Female buffaloes of proven fertility (n = 30), 4–8 years of age and body condition score of 3–4.5 (scale 1–5), were used. The animals were grazed on natural pasture, with water and minerals available ad libitum. Buffaloes were divided in three groups, for presynchronization: G1, intravaginal device of P4 of 0.6 g (Dispocel, Von Franken) plus 2 mg of estradiol benzoate (BE; Von Franken); G2, injection of 4 mL of a commercial preparation of P4 and BE intramuscularly (50 and 0.56 mg mL⁻¹, respectively); and G3, control without any treatment. On Day 7, all animals received 2 mL of d-cloprostenol (0.150 mg Destrogenol, Von Franken) was administered. On Day 14, all buffaloes were synchronized using Ovsynch protocol (GnRH + prostaglandin + GnRH) and inseminated 1 h after the last injection; nonpregnant animals were reinseminated 28 days later. On Day 14, antral follicle count and corpus luteum (CL) determination were evaluated using a portable ultrasound machine with a linear probe 7.5 MHz (Mindray, DP30-Vet). On Day 60 after FTAI, pregnancy was evaluated. The data from the ovaries on Days 7 and 14 and the pregnancies were recorded, and the results of pregnancies were evaluated using a comparison of proportions. A value of P < 0.05 was considered statistically significant. On Day 14, the G1, G2, and G3 groups presented 10.3 ± 2.8, 8.9 ± 3.3, and 8.1 ± 3.9 follicles, respectively, with no significative differences between groups. Pregnancy rates were 90%, 60%, and 40% from the G1, G2, and G3 groups, respectively; G1 was statistically different compared with the control and vaginal P4 (P = 0.0223). The proportion of CLs obtained was 50%, 60%, and 60% and the pregnancies in animals with CL were 100%, 33%, and 66% for G1, G2, and G3 groups, respectively; the number of CLs was not statistically different between groups, but pregnancy rates were higher in G1 (P = 0.09) compared with vaginal P4 and not statistically different from the control (G3). It can be concluded that the different forms of P4 evaluated do not have a different effect over CL presentation and pregnancy; however, this species presents paradoxical responses to medications. There are no explanations for the fact that the pregnancy rate was better in animals receiving the injected progesterone and in the controls. The CLs generated with vaginal P4 did not generate pregnancies. In this case, the control had no differences compared with treatments, Finally, the authors propose that the difference in response is associated with metabolic processes of the animals, rather than an effect on the target organs themselves or the presentation. Presynchronization does not necessarily improve pregnancy rates.