To improve on-farm reproductive performance when using artificial insemination (AI), semen should be periodically screened for several factors before processing for use.
The screening ensures boar output is optimized and that quality matings are possible, notes Kevin Rozeboom, Extension specialist, swine reproductive physiology, North Carolina State University.
Table 1 lists semen quality standards in the "normal" and "minimally accepted" value ranges. Below, Rozeboom explains the four major parameters used to evaluate semen.
Volume Or Concentration The entire ejaculate should be 100-500 ml, minimal level of 50 ml.
Laboratories use a machine that counts sperm called a spectrophotometer. Dilute the semen in most boars 1 part semen to 10 parts extender to provide an accurate sperm count range, says Rozeboom.
Experts suggest that semen volume is not an accurate assessment of fertility, he points out. It is only used as a tool to monitor the health and productive output of the boar.
But volume is still used as the main selection criteria for boar semen, notes Rozeboom. Producers are gradually reducing sperm dose numbers, some to 2 billion and less sperm per dose, in order to optimize breeding performance. Research suggests that as few as 1 billion inseminated sperm can adequately fertilize females in optimum conditions.
"If you think you are putting 2 billion in and you are (really) only putting half of that in, you may be suffering some reproductive problems due to the low numbers of sperm inseminated," warns Rozeboom.
That makes accurate sperm counting for AI use much more critical, he emphasizes. Use a spectrophotometer if you have one, or at least use a microscope, to get an idea if that collection is alive or dead.
Besides sperm counting, an evaluation of sperm motility or activity is probably the only major test of semen viability done by AI boar semen labs, says Rozeboom.
Motility Take a drop of raw semen or semen diluted 1:1, place it on a warmed slide (98.6 to 102 degrees F.) and view it under a microscope. Look for a swirling action and sperm cells that are moving forward. This is the most widely used means of checking sperm cell activity. It takes a trained eye and experience to become adept at this procedure.
"Some cells may appear to be moving but it is just other cells pushing them around," says Rozeboom.
Motility appears to be a key part of a semen evaluation. Late '90s research says farrowing rates and litter sizes will decrease if initial semen motility is recorded at below 60%.
Morphology Sperm cells may appear active but, if they are improperly shaped, they may not be able to fertilize eggs, says Rozeboom.
"Generally, when we do a morphological exam, we will count 100-200 (sperm) cells and take the percentage of normal heads vs. abnormal sperm heads," he explains. Ejaculates of less than 70% normal sperm cells are considered inferior collections.
A rough morphological exam can be done the same time as semen motility provided you have a phase contrast microscope, according to Rozeboom. Use a semen sample diluted 1:10 with formal saline and viewed under oil immersion. Count deformities are listed in Table 1.
Acrosome Integrity Acrosome is a layer that covers the sperm head. When it loses integrity, it separates from the sperm head or it may be missing completely.
Remember, these four parameters are signs of sperm viability and not necessarily sperm fertility. If you have boar fertility problems, have an experienced technician check daily processing of boar semen.