Impact of supplementation with long-acting progesterone on gestational loss in Nelore females submitted to TAI.

The goal of this study was to evaluate the effect of long-acting progesterone supplementation on pregnancy rates and gestational losses in Nelore females (Bos taurus indicus) submitted to Timed Artificial Insemination (TAI). Ovulations of multiparous (n = 534), primiparous (n = 117) and nulliparous (n = 81) Nelore females were synchronized for TAI and the day of insemination was considered D0. After TAI, the animals were allocated into three groups. Two groups received 150 mg of long acting injectable progesterone (P4) in a single dose, 5 (D = 5) or 11 (D = 11) days after TAI, resulting in the following treatments: 1) Group P4 - D5 (n = 235); 2) Group P4 - D11 (n = 245); and 3) Control Group (n = 252). The animals in the control group did not receive any supplementation. Pregnancy was checked by ultrasonography, 30 days after the TAI. The gestational losses were evaluated at two different periods: 1) from 30 to 60 days, and 2) from 60 to 90 days. The pregnancy rate and the gestational losses as a function of the treatments were tested by the non-parametric binomial test with 5% significance level. The pregnancy rates were different between the groups P4 - D5 and Control (47 and 39%, respectively) (P < 0.05), but no difference was observed in relation to the P4 - D11 group. There was a difference in gestational losses from 30 to 60 days and total losses between the groups treated with P4 on the fifth day and eleventh day after TAI in relation to the control group (P = 0.0173; P = 0.0454), but no difference was observed between the treatments in relation to the losses between 60 and 90 days (P ≥ 0.0578). Among the animals that were cycling at the beginning of the protocol, the groups supplemented with progesterone at day 5 or 11 after insemination had gestational losses significantly lower (P = 0.04) than the control group (P4 - D5 = 2%; P4 - D11 = 2%, control = 14%). The animals in anestrous that received supplementation 5 days after TAI had lower gestational losses (P = 0.049) compared with the other groups (P4 - D5 = 3%, P4 - D11 = 7% Control = 10%). Under the conditions of this study, the use of long-acting injectable progesterone 5 days after TAI in Nelore females increased the pregnancy rates, but when supplemented 11 days after TAI, it did not have the same effect. Also, when used 5 days after TAI, it significantly decreased gestational losses on both anestrous and cycling animals. Therefore, it may be an interesting alternative to increase reproductive and productive efficiencies.
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