262 EFFECT OF SYSTEMIC ANTIOXIDANT TREATMENT IN BOS TAURUS TAURUS BULLS UNDER HEAT STRESS AND SUPPLEMENTED WITH POLYUNSATURATED FATTY ACIDS

Abstract

One reason for lower fertility of European bulls in tropical regions is a higher rate of oxidative stress caused by increased production of reactive oxygen species (ROS) not compensated by antioxidant protection. In that regard, sperm are extremely susceptible to oxidative stress due to a high concentration of polyunsaturated fatty acids (PUFA) in their plasma membranes. However, the presence of these PUFA is fundamental for sperm to be fertile and resistant to cold shock. Thus, treatments that suppress oxidation may increase productivity of these animals. This study aimed to evaluate the most damaging ROS for European bulls subjected to heat stress and to determine a possible antioxidant-targeted treatment. In a second step, we sought to verify the efficiency of the interaction between a diet rich in PUFA and a targeted antioxidant treatment on the quality of ejaculated and epididymal sperm in European bulls subjected to testicular heat stress. Four Bos taurus bulls were subjected to scrotal insulation for 5 days, with semen collection (electroejaculation) 60 days after insulation. Semen from each bull was divided into 4 aliquots and subjected to 4 ROS-generating systems: superoxide anion (xanthine/xanthine oxidase), hydrogen peroxide, hydroxyl radical (ascorbate + ferrous sulfate), and malondialdehyde (MDA; lipid peroxidation product). Samples were incubated for 1 h and assessed by computerized sperm analysis (CASA); eosin/nigrosin (membrane integrity); fast-green/Bengal rose (acrosome integrity); 3,3′ diaminobenzidine (mitochondrial activity); sperm chromatin structure assay (DNA fragmentation); and thiobarbituric acid reactive substances (lipid peroxidation). Overall, MDA had the most deleterious effects on semen quality of Bos taurus bulls subjected to acute heat stress. Thereafter, 16 bulls were subjected to testicular insulation and allocated into 4 groups: control (n = 4; given mineral oil; placebo); vitamin E (n = 4, given 5 mL of Monovin® every 13 days); PUFA (n = 4; given 4 kg day^–1 Megalac®); and PUFA+vitamin E (n = 4; combination of PUFA and vitamin E treatment groups). Semen was collected on the day of installation of the insulation, on the day it was removed, and 30 and 60 days later. Overall, vitamin E reduced heat stress-induced damage to sperm DNA and mitochondria, but only in samples collected from the epididymis. Similarly, the combination of vitamin E and PUFA supplementation improved sperm motility patterns. Therefore, a combined antioxidant treatment (vitamin E and PUFA) may reduce damage to sperm caused by acute heat stress in European bulls. However, this treatment may be more effective if instituted before heat stress.