Uso de sêmen bovino incubado a diferentes temperaturas após o descongelamento em protocolo de inseminação artificial em tempo fixo

Abstract

This thesis aimed to evaluate the feasibility of using thawed bovine semen subsequently refrigerated at different temperatures, with a view to its application in fixed-time artificial insemination (FTAI) protocols in remote regions of the Amazon. In Chapter II, a literature review on lipids in bull reproduction was conducted, highlighting the role of polyunsaturated fatty acids, cholesterol, and phospholipids in sperm membrane fluidity and integrity, motility, and resistance to oxidative stress. This review evidenced that semen lipid composition is a key determinant of fertility. Feeding bulls with different types of fatty acids can positively influence semen quality parameters; however, results vary according to the type of fatty acid used, the route of administration, and its quality. In Chapter III, the viability of thawed commercial bovine semen stored under refrigeration at 5 °C or 15 °C was evaluated. Sperm motility, vigor, and morphology were assessed over 48 h of incubation, in addition to longevity determined by the slow thermoresistance test at 38 °C for 5 h. In the field, 100 cows were inseminated with doses maintained at 5 °C for 10 h or with conventionally frozen semen. Laboratory results indicated a progressive reduction in motility and vigor over time (P < 0.0001), although within acceptable limits for use in artificial insemination (AI). No significant differences were observed between 5 °C and 15 °C (P = 0.9927). In field trials, pregnancy rates also did not differ between groups (P = 0.8760). Thus, post-thaw refrigeration between 5 °C and 15 °C preserves sperm quality for sufficient time to allow its use in FTAI, without impairing fertility. This approach represents a cost-effective and logistically feasible alternative for production systems with limited access to cryogenic infrastructure. By integrating biochemical foundations of sperm physiology with applied solutions for tropical livestock, this thesis contributes to scientific advancement and to the improvement of productive efficiency in regions of strategic relevance for food security and sustainable development.