Veterinarians and breeding farm managers regularly examine stallion semen samples under a microscope to check sperm motility, especially samples from horses with suspected fertility issues. But while they can check sperm for this common fertility measure on the farm or in the average veterinary clinic, evaluating sperm morphology--to ensure the head, midpiece, and tail are appropriately shaped--is a more difficult process they often skip. University of Florida (UF) researchers recently studied the plausibility of using an inexpensive, efficient method for examining sperm morphology.
Some laboratories that analyze semen samples maintain equipment for conducting phase-contrast microscopy to assess morphology, noted Malgorzata Pozor, DVM, PhD, Dipl. ACT, of the UF's Department of Large Animal Clinical Sciences, at the 2012 American Association of Equine Practitioners' Convention, held Dec. 1-5 in Anaheim, Calif. "It is an accurate technique that is superior to many other methods, such as eosin-nigrosin staining, for identifying abnormalities in the midpieces, head, and acrosome (a specialized structure on the head of the sperm that helps penetrate the egg during fertilization)," she said.
The problem is that some veterinarians prefer to perform semen analysis on-site, rather than sending the sample to specialized laboratories. Further, phase-contrast microscopes are expensive. Bright-field microscopes are far more economical and are already standard fixtures in most veterinary practices.
"Being able to accurately assess sperm morphology using bright-field microscopy rather than phase-contrast microscopy would be beneficial," noted Pozor.
Although several research teams previously attempted to identify stains and staining techniques amenable to bright-field microscopy, no published protocol for staining stallion spermatozoa using "quick n' easy" stains such as Dip (Diff) Quick exists. So Pozor and colleagues collected 24 ejaculates and analyzed the sperm using three different techniques: traditional phase-contrast microscopy; eosin-nigrosin staining then analysis withbright-field microscopy; and Dip Quick staining and analysis via bright-field microscopy. There are three separate stains used in Dip Quick staining, and the researchers also looked at whether five, 15, or 30 minutes of staining with Dip Quick was better. Their key findings:
- All spermatozoa defects that they identified using both phase-contrast and eosin-nigrosin staining were also identifiable in samples stained with Dip Quick; and
- Exposing slides to each of the three Dip Quick solutions for 30 minutes (rather than five or 15 minutes) enhanced the researchers' ability to see the sperm head and acrosome region.
"Unfortunately, no acrosome abnormalities were detected via either phase-contrast or bright-field microscopy in this study, which means we were unable to assess the usefulness of detecting acrosome abnormalities," said Pozor.
However, Pozor noted that only fertile stallions with good-quality semen were used in this study, which could explain the lack of acrosome abnormalities. Additional studies involving less-than-perfect stallions that produce semen with various defects are needed.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.