Researchers at the University of Illinois have developed a new approach to fertility testing boar semen samples. The new process amounts to racing the sperm collected from two different boars.
Andrea Braundmeier and David Miller are testing this new approach to semen testing in the laboratory. “The ability to estimate the fertility of an ejaculate prior to processing and insemination is valuable for improving reproductive efficiency,” Miller explains. “Knowing the fertility of a semen sample, one could remove subfertile males or low quality semen collections and thereby improve herd fertility.”
To date, most laboratory fertility tests involve a microscopic examination of sperm to estimate the motility and viability of a sample. A second type of examination identifies defects in sperm structure that are associated with reduced fertility. “These assays are simple and inexpensive, but there are many semen samples that appear normal based on these criteria, that are still subfertile,” says Miller. “Therefore, it is important to determine the most common defects in these samples and incorporate methods to assess these defects into routine semen evaluation.”
Their answer to the fertility riddle is to measure the ability of sperm to fertilize eggs using a modification of in vitro fertilization. Although this laboratory method of fertilization is not new, the research team has designed a competitive assay in which the sperm from two different collections or two different boars are mixed together and then allowed to fertilize the eggs from a single female.
To identify which sperm are the most successful, the separate sperm collections are stained with two different fluorescent dyes. Much as two sprinters run under the same conditions on a track, the two semen samples are exposed to exactly the same conditions and are allowed the same opportunity to fertilize the same eggs.
Initially, Braundmeier and Miller measured the ability of sperm to bind to the protein coat surrounding the egg, known as the zona pellucida. They obtained semen from a number of boars and are testing them in a pair-wise fashion.
For example, they are comparing Boar A and Boar B, and then comparing Boar B and Boar C. Boars A and C can then be compared indirectly, based on the competition with a common partner, Boar B. An overall ranking can then identify the animals whose sperm have the greatest zona pellucida binding ability. Research in progress will determine if that binding ability is related to the actual fertility of the boars.
The long-term goal is to identify the specific defects in sperm that most often cause reduced fertility. Once those defects are identified, more precise tests to diagnose fertility can be designed. Ideally, a simple laboratory test could analyze each semen collection before processing. If such a test were developed, it could dramatically improve swine fertility.