By W.L. Flowers, North Carolina State University Department of Animal Science
Poor semen quality can result from mistakes during collection and extension of semen or from mismanagement of boars. The end result of both is low motility, poor morphology and ejaculates that can’t be used for insemination. Unfortunately, there are no unique morphological changes that occur in the sperm cells themselves that can be used as a reliable differential diagnosis in “real time.”
This makes it difficult to determine the causes of low sperm quality by simply examining individual ejaculates. One of the best ways to discriminate between semen handling or people problems from those related to the boars themselves is to study changes over time. Since most boar studs record individual semen output in computer databases, it is fairly easy to track changes over time.
The pattern of how quickly sperm production recovers after a poor ejaculate is the key to determining whether the problem occurred during collection and extension or is something that affected the boar.
Spermatogenesis is a continuous process that from beginning to end takes between five to seven weeks in the boar. There are always cells that have just begun to develop; cells that are close to being mature; and cells at all stages in between. When a boar is subjected to poor management conditions such as heat stress, disease, etc., the majority of the spermatozoa undergoing development are affected. Consequently, it usually takes sperm production about five weeks to return to normal after the stress on the boar has been alleviated. This can vary somewhat depending on the severity of the stressor.
In contrast, problems with collection and extension typically only affect the current ejaculate. As a result, sperm production typically returns to normal immediately or, at least, within a time period considerably less than five weeks unless it is repeated continuously. This is due to the fact that the problem is not really affecting the boar, but the semen once it is ejaculated.
The figure below shows characteristic changes in normal sperm production for each of these situations.
The red line indicates 70% motility which is often used as the minimum acceptable level for ejaculates. Motility was below 70% during the weeks before and after July 29. These are clearly semen collection/extension problems because semen quality returned to normal within a week.
In contrast, during the week before Aug. 26 something affected the boar. Motility remained suboptimal (below 70%) for a period of five weeks until the middle of September.