The purpose of this study was to describe morphological and quantitative aspects of preantral and antral follicles in the equine ovary. Six ovaries were collected from necropsied mares and sliced lengthwise parallel to the ovulation fossa. The slices were fixed and processed for histological evaluation under light microscopy. Preantral follicles were classified according to developmental stage and as morphologically normal or degenerated. Also, another 183 ovaries were obtained from an abattoir. From these ovaries, antral follicles were measured, punctured and oocytes evaluated. Oocyte recovery rates were calculated for each follicle size category. A total of 490 preantral follicles were examined. Primary follicles were in greater number than primordial follicles. No secondary follicles were identified. A total of 518 antral follicles were punctured and evaluated. Total oocyte recovery rate from antral follicles was 47.6. In conclusion, preantral follicles consist of a scarce source in the equine ovary. Antral follicles oocyte recovery rate was higher for smaller-diameter antral follicles.

RESUMOO presente estudo teve como objetivo avaliar o efeito da condição corporal (CC) sobre a eficiência reprodutiva e a dinâmica folicular de éguas, no decorrer da estação de monta. Foram acompanhadas 134 éguas (92 não lactantes e 42 lactantes) que, em novembro e dezembro, foram submetidas à inseminação artificial e, de janeiro a março, à monta natural controlada, em dias alternados. Mantidas sob rufiação diária em grupo e a campo, quando o cio era detectado, iniciou-se o controle folicular diário por palpação trans-retal até a detecção da ovulação. O escore da CC foi avaliado nos meses de agosto, novembro, janeiro e março. A taxa de anestro foi 26,11% e a de gestação 56,7%, mas, considerando-se apenas as éguas cíclicas, 77% tornaram-se gestantes. O número de ciclos/concepção foi 2,3 e de saltos/ciclo 2,1. Houve efeito (P<0,05) da evolução da CC sobre o número de éguas cíclicas e a taxa de gestação. O mês da estação de monta e a CC influenciaram todas as características foliculares e a taxa de gestação (P<0,05). Concluiu-se que a condição corporal tem efeito sobre a atividade cíclica, a dinâmica folicular e a fertilidade de éguas.

This study used Nelore embryo donors to evaluate the effects of summer temperatures and humidity in a tropical area on embryo recovery. Seventeen cows were randomly assigned to three groups (G1, G2 and G3) as well as 28 heifers into four groups (G4, G5, G6 and G7), and underwent a consecutive 4 d superovulation protocol (Day 0 to 3) and two artificial inseminations (AI; Day 4 and 5). Cortisol concentrations were determined on Day 0, 4 and 5. Temperature and humidity index (THI) was recorded from Days 0 to 7. Embryos were recovered on Day 11, and evaluated for quality and quantity. Heifers experienced higher thermal load than cows, however, there was no difference in the cortisol and reproductive parameters measured between both. The THI measured throughout the experiment oscillated between 65.8 and 85.2 (76.1 ± 3.9), which is a dangerous range for thermal comfort, especially above 78. Animals from G5 were subjected to high THI throughout the experimental protocol, approaching a dangerous condition (78.7 ± 0.9) on Day 4 (first AI). The THI for G2 cattle was also high, as in the other groups, but increased to over 80 two days after AI. Animals from group G5 had the lowest viable production being 2.4 ± 0.9 embryos (38% of viability), followed by cattle from group G2 (3.0 ± 0.9 viable, P<0.05). Thus, high thermal load in the summer expressed by high THI, on the day and post- insemination days (during embryo cleavage), compromises embryo numbers, viability and consequently reproductive performance of Nelore females.