Abstract
ABSTRACT This study evaluated the plasma membrane integrity, acrosomal membrane integrity, and mitochondrial membrane potential of Nelore bull sperm from early puberty to early sexual maturity and their associations with sperm motility and vigor, the mass motility of the spermatozoa (wave motion), scrotal circumference, and testosterone. Sixty Nelore bulls aged 18 to 19 months were divided into four lots (n=15 bulls/lot) and evaluated over 280 days. Semen samples, collected every 56 days by electroejaculation, were evaluated soon after collection for motility, vigor and wave motion under an optical microscope. Sperm membrane integrity, acrosomal integrity, and mitochondrial activity were evaluated under a fluorescent microscope using probe association (FITC-PSA, PI, JC-1, H342). The sperm were classified into eight integrity categories depending on whether they exhibited intact or damaged membranes, an intact or damaged acrosomal membrane, and high or low mitochondrial potential. The results show that bulls have a low amount of sperm with intact membranes at puberty, and the sperm show low motility, vigor, and wave motion; however, in bulls at early sexual maturity, the integrity of the sperm membrane increased significantly. The rate of sperm membrane damage was negatively correlated with motility, vigor, wave motion, and testosterone in the bulls, and a positive correlation existed between sperm plasma membrane integrity and scrotal circumference. The integrity of the acrosomal membrane was not influenced by puberty. During puberty and into early sexual maturity, bulls show low sperm mitochondrial potential, but when bulls reached sexual maturity, high membrane integrity with high mitochondrial potential was evident.
Highlights
The sexual development of bulls from puberty to sexual maturity is characterized by remarkable changes in the physical features of the animal as well as the quality of its semen
The sperm were classified into eight integrity categories depending on whether they exhibited intact (IMe) or damaged plasma membranes (DMe), intact (IA) or damaged acrosomal membranes (DA), and a high (HM) or low (LM) mitochondrial membrane potential
Hormonal changes occurring throughout sexual development are a remarkable aspect of the onset of puberty in bulls
Summary
The sexual development of bulls from puberty to sexual maturity is characterized by remarkable changes in the physical features of the animal as well as the quality of its semen. Sperm motility, sperm vigor, and wave motion increase with maturity before reaching a plateau, which improves the potential for fertilization (Neto et al, 2011). The maintenance of the sperm fertilization potential depends on the integrity and functionality of different cellular structures. Plasma membrane integrity is crucial for sperm survival inside the female reproductive tract to maintain the fertilization capability and the cell’s osmotic equilibrium, and acting as a barrier between the intra- and extracellular media (Flesh and Gadella, 2000). Acrosomal integrity and enzyme maintenance are essential to the acrosomal reaction (Flesh and Gadella, 2000) and membrane fusion is required for sperm-oocyte fusion even though sperm membranes are fixed to oocytes in the free zone and the occurrence of fertilization (Hafez, 2004).
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