By W.L. Flowers, North Carolina State University Department of Animal Science
The hot, humid environment associated with the summer months is fast approaching and many operations are making plans accordingly. Most research, to date, has focused on how one aspect of the production environment affects sperm production in boars, for example, elevated temperatures or increased collection frequencies. These studies are crucial from a scientific perspective, but probably don’t represent what happens in commercial studs since boars are likely exposed to a number of factors simultaneously, most of which could have a negative effect on sperm production.
Since an animal’s response to “environmental stressors” is manifested through the same physiological pathway it is reasonable to assume that their effects are additive. What this means from a practical perspective is that, the presence of several “low-level stressors” may have the same effect as one “high-level stressor.” In other words, the effect of stressors on sperm production is additive.
Data from several different commercial boar studs is shown in Table 1 that illustrates this point. In this study, “stress assessments” were conducted in four, 250-head boar studs. The normal production environment including routine management practices were evaluated and classified as either having a chronic or acute, negative effect on sperm production. For example, exposure to temperatures between 26 and 29 degrees C for an extended period was considered a chronic stress, while exposure to higher temperatures for shorter periods of time was classified as an acute stress. Inconsistent collection frequencies, vaccinations, changes in housing within the boar stud, changes in collection technician, feed quality and routine blood sampling were several of the management conditions that can occur in boar studs that were considered to be possible stressors in this study.
Several important relationships are evident from these data. Firstly, there is variation in terms of how boars in different studs respond to the same relative stress load. This should not be surprising since there are genetic differences in terms of how sperm production in boars responds to stressors and, obviously, the severity of each individual stressor may have differed among studs.
Secondly, relative changes in the number of potential stresses appear to be more important than the actual number to which boars are exposed with regards to their overall impact on sperm production. For example, the number of ejaculates rejected due to poor sperm quality was greater in Stud B when the stress level increased from 0 to 2 compared with Stud D where it increased from 2 to 3. This is particularly relevant if the difference between the winter and summer months for Stud D are evaluated. In this particular operation, the stressor level increased from 0 to 6 and resulted in the largest increase in rejected ejaculates due to poor quality, 4.5% versus 35.4%.
These data should be viewed as preliminary, but they do represent conditions to which most commercial boars are exposed. Therefore, assessment of the potential stress load in studs seems to be a practical and proactive approach to prevent reductions in the production of quality sperm. Consequently, if the hot, humid environment associated with the summer months is considered to be a significant stressor which really is beyond the control of boar stud personnel, then reducing the occurrence of others which can be controlled by management such as vaccination and blood sampling schedules may prove to be an effective way to mitigate some of the reductions in sperm quality normally associated with the summer months.