140 Evaluation of the use of injectable progesterone for presynchronization of ovulation in fixed-time artificial insemination programs in water buffaloes

Owing to difficulty of detecting estrus and the need for productive and reproductive management, fixed-time AI (FTAI) has become a common tool in buffalo herd management. Vaginal devices impregnated with progesterone (P4) have been used with success to synchronize the emergence of follicular wave and ovulation. Recently, an injectable pharmaceutical form of P4 and estradiol (E2) has been developed. This study compare the effect of two forms of presentation of P4 on presynchronization (presynch) of the ovary in an FTAI program in buffaloes. This study was conducted at the Pedro Antonio Silva (h) farm located in General Paz, Corrientes Province, Argentina (27°20′33″S latitude and 58°08′27″W longitude) at the end of the non-breeding season (February 2024). Buffalo females of proven fertility (n = 30) that had a body condition score between 3 and 4.5 (scale 1–5) and a normal reproductive tract were choosen. They were grazed on natural pasture with water and minerals ad libitum. Three groups of 10 animals were randomly allocated. Group 1 (G1) received an intravaginal device of P4 of 0.6 g (Dispocel, Von Franken) plus 2 mg of estradiol benzoate (Von Franken) for presynch; group (G2) received 4 mL of a single injection of P4 and estradiol benzoate (50 mg and 0.56 mg mL⁻¹, respectively) intramuscularly (i.m.) for presynch; and group (G3) control did not receive any treatment for presynch. On Day 7 all animals received 2 mL of of d-cloprostenol i.m. (0.150 mg of Destrogenol, Von Franken). On Day 14, antral follicle count and corpus luteum (CL) determination were performed using a portable ultrasound machine with a linear probe (Mindray, DP30-Vet). The data from Day 7 and 14 were recorded in an Excel sheet, and the groups were compared using ANOVA and the comparison of proportions. A value of P < 0.05 was considered statistically significant. At the beginning of the experiment, G1, G2, and G3 animals presented (mean ± SD) 5.8 ± 1.9, 8.7 ± 4.2, and 6.6 ± 3.8 follicles, respectively; on Day 14, they presented 10.3 ± 2.8, 8.9 ± 3.3, and 8.1 ± 3.9 follicles, respectively. No significant differences were found between the groups. In G1, a tendency to present CL (P = 0.08) was observed. The treatments did not alter the follicular dynamics of the animals, as evidenced by the absence of significant differences in the number of antral follicles between the compared groups and CLs (P < 0.05). The conclusion is that the different presentations of the medications did not have a different effect, which makes it necessary to evaluate other parameters to make decisions about their use. However, contrary to expectations, G1 animals were found to have 10.3 ± 2.8 follicles at the end of the experiment, compared with 5.8 ± 1.9 at the beginning; this difference was significant (P = 0.003). The response rate was still low, and given their observed impact on follicular development, the application of drugs and protocols designed for cows should be evaluated first in buffaloes to obtain the maximum benefits and to ensure the best pregnancy rates.