Description: Ten differential interference contrast micrographs of bull sperm with abnormal tails. Bull sperm heads are flat, about 10 microns long, 5 microns wide and 0.5 micron thick. The tail including the middle piece is about 60 to 70 microns long. It tapers from about 0.75 micron in diameter at the middle piece to about 0.25 micron at the proximal terminal piece. Image A, Vestigial middle piece (arrow); Image B, Abaxial middle piece, not centered on the head; Image C, Double tail; Image D, Tail reflected back and forth; Image E, Filiform (abnormally slender) middle piece; Image F, Broken middle piece; Image G, Bent middle piece; Image H, Broken neck; Image I, Tail tightly coiled; and Image J, Defective middle piece with abaxial implantation and missing mitochondrial coils near neck. Technicians in commercial artificial insemination laboratories look for these kinds of sperm tail defects while evaluating semen quality. While less than 5% of sperm with these defects is not alarming, more than 10% of sperm with these kinds of defective tails suggest semen samples with reduced fertility. NAL #5087 illustrates greater structural details of sperm.