Summary:The study aimed to evaluate the effect of double administration of a progesterone (P4) intravaginal device on induction of ovarian cyclicity in mares. Twelve crossbred mares were assigned to one of two groups. The first group (GP4; n = 6; 100 % in anestrus phase) underwent the following protocol: day (d) 0, 1.9 g of P4 + ultrasound of the uterus and ovaries (US); d 7, US; d10, first P 4 removal + US; d10 -d 24, US daily; d 28, second P4; d 35, US; d 40, second P4 removal + US; d 40 -d 54, US daily; and d 54 -d 76, US every other day. The second group (GNP4; n = 5; 100 % in transition phase) underwent the same protocol as GP4, but without the administration of the P4 device. From d 55 -d 76, 100.0 % of the mares in both groups held uterine tonus and 83.3 % had endometrial edema; after the first and second P4 removal, 66.7 % and 83.3 % of GP4 mares, respectively, reached the transition phase. By d 76, 50.0 % and 80.0 % of the GP4 and GNP4 animals, respectively, had ovulated; the average size of the largest follicle increased from d 0 -d 76 in both groups, but was significant only in GP4. Four to five days after the first and second P4 removals in GP4, follicles showed an average growth of 9.0 mm. At the end of the study, both groups had follicular medium diameters greater than 34 mm (P > 0.05). Ovulations correlated with body condition scores (P < 0.05). In conclusion, two administration of P4 affected ovarian cyclicity in anestrous mares, and synchronized follicular waves and ovulation.

Timed artificial insemination (TAI) has boosted the use of conventional artificial insemination (CAI) by employing hormonal protocols to synchronize oestrus and ovulation. This study aimed to evaluate the efficiency of a hormonal protocol for TAI in mares, based on a combination of progesterone releasing intravaginal device (PRID), prostaglandin (PGF2α) and human chorionic gonadotropin (hCG); and compare financial costs between CAI and TAI. Twenty‐one mares were divided into two groups: CAI group (CAIG; n = 6 mares; 17 oestrous cycles) and TAI group (TAIG; n = 15 mares; 15 oestrous cycles). The CAIG was subjected to CAI, involving follicular dynamics and uterine oedema monitoring with ultrasound examinations (US), and administration of hCG (1,600 IU) when the dominant follicle (DF) diameter's ≥35 mm + uterine oedema + cervix opening. The AI was performed with fresh semen (500 × 106 cells), and embryo was recovered on day 8 (D8) after ovulation. In TAI, mares received 1.9 g PRID on D0. On D10, PRID was removed and 6.71 mg dinoprost tromethamine was administered. Ovulation was induced on D14 (1,600 IU of hCG) regardless of the DF diameter's, and AI was performed with fresh semen (500 × 106 cells). On D30 after AI, pregnancy was confirmed by US. The pregnancy rate was 80.0% in TAIG and 82.3% in CAIG (p > .05). The TAI protocol resulted in 65% reduction in professional transport costs, and 40% reduction in material costs. The TAI was as efficient as CAI, provided reduction in costs and handlings, and is recommended in mares.

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The present study was designed to assess the effect of conventional artificial insemination (CAI) and deep intrauterine artificial insemination (DAI) using different concentrations of spermatozoa on the production of embryos in mares during two breeding season (BS). Seventy-four estrus cycles from 13 crossbred mares (Criollo/English Thoroughbred/Quarter horses) were evaluated, considering the location of semen deposition and doses of fresh semen. The animals were assigned to two treatments: treatment CAI (AI on the uterine body; n = 38) and treatment DAI (AI at the apex of the uterine horn, ipsilateral to an ovary with a preovulatory follicle (POF); n = 36). The animals in estrus were evaluated by ultrasonography to measure the dimensions of the POF. It was observed that POF was larger than 33 mm in diameter than uterine edema and a cervical opening grade of 3, 750 mg of deslorelin acetate (IM) was injected. Twenty-four hours later, AI was performed. The CAI mares received 500 ×10 6 progressively mobile spermatozoa (PMS) and the DAI mares received 250 ×10 6. Embryo collection occurred on days 7 or 8. The embryo recovery rate (ERR) was 68.4 % (26/38) for CAI and 72.2 % (26/36) for DAI. No significant difference was found for the ERR for either of the two AI methods or the sperm doses used. In conclusion, both AI methods can be used successfully in horses and it is possible to reduce the dose of PMS by 50 % when using DAI without decreasing the fertility rate. The production of embryos may be performed several times during the breeding season in the same mare.