Sperm Morphology

Morphology alone is not highly correlated to fertility of an ejaculate. However, the percent of morphologically normal sperm does add information when looking at the fertility of a stallion when taken into account with motility, % live sperm and DNA integrity.

More importantly, changes in the % normal sperm indicate a change in the function of the stallion's testes or epididymis (due perhaps to a change in health). When any male has a high fever (or any heat stress), there are changes in sperm formation and stored sperm that are reflected in decreased normal morphology. Because of the time from sperm formation to ejaculation, abnormal sperm may persist for up to two months.

Most stallion owners are not equipped or trained to do a morphology test and rely on veterinary clinics to do an annual semen morphology test, if at all. You will have the opportunity to look at phase-contrast images to learn to evaluate morphology. Look at the sperm in the images and decide if they have normal morphology. Use the chart from the lecture to determine primary, midpiece and tail abnormalities. A sperm can have more than one abnormality. (These samples were fixed in 0.5% paraformaldehyde, dried on slides and coverslips permanently mounted. Wet mounts (sperm fixed, stained and put on slides to be immediately evaluated) can also be used to determine morphology.

	Normal Normal, junk on head Normal Normal Malformed midpiece, normal head Broken midpiece Normal 5/7 normal (71%) Although this is too small of a sample to make a conclusion, the quality of semen is ok. 100-200 cells should be counted to accurately determine % normal morphology.
	This is another field of the sperm from the same stallion. Pyriform Normal Normal Normal Malformed head and midpiece Normal Head with no tail, primary defect 4/7 normal (57%)
	This is another field of the sperm from the same stallion. broken midpiece, secondary defect Normal Pyriform Normal Normal Normal Abnormal head and midpiece Normal Normal Normal Normal not enough of tail showing to evaluate 8/11 normal (73%)   Total for all 3 fields 17/25 normal (68%) For a complete evaluation we would count at least 100 - 200 sperm.

Now you are ready to review semen evaluation.