Dinâmica folicular em éguas sob utilização do dispositivo intravaginal de progesterona na transição primaveril

Abstract

The absence of well-defined cycles and precise ovulations due to the strong characteristic of horses to be dependent on positive photoperiod, makes it impossible to use and make the most of mares in reproductive programs in the periods leading to the end of the breeding season, resulting in low utilization of advanced reproductive biotechnologies. An alternative to circumvent and delay the entry of seasonal anestrus in these animals is the use of a progesterone (P4) implant, allowing the endocrine activity in the mare to remain normalized for a longer period of time. The objective of the study was to evaluate the follicular dynamics in relation to the use of the 20g P4 intravaginal device for twelve days, during the autumnal transition period, which may increase the proportion of mares exhibiting follicular development typical of estrous cyclicity, making it possible to estimate a previous ovulation date after removal of the device, without the use of any ovulation-inducing drug. The project was carried out at Queixada, Lavras, Minas Gerais, from April to June 2023. Sixteen Mangalarga Marchador mares, aged 4 to 15 years and with a body condition score (BCS) of 1 to 9, were used. The animals were divided into a control group (CG) and a treatment group (TG), with a changeover performed between the groups. The follicular dynamics of the animals were monitored by periodic ultrasounds, measuring the size of the largest follicle present in all exams, in addition to blood collection to assess P4 concentration. The results were compared during the two experimental batteries of the changeover as well as between the CG and TG, considering P<0.05. No ovulation was observed during the permanence of the P4 device in both experimental periods and groups. The ovulatory rate of the GT in the first experimental phase was 100% versus 31% of the CG, while in the second experimental phase, where the animals were already in seasonal anestrus, it was 19% in the GT and 13% in the CG. The GT animals ovulated 5.54 ± 0.45 days after removal of the device. The present study demonstrated the applicability and efficiency of the P4 intravaginal device in follicular control in mares at the beginning of the autumn transition period.