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Seasonality May Affect Semen Quality in StallionsBy Kentucky Equine Research Staff · June 20, 2017

Artificial lighting to increase the photoperiod (day length) helps advance the breeding season in mares to produce foals early in the calendar year. In stallions, semen quality also changes based on season and photoperiod. One research group* recently questioned whether other factors, such as ambient temperature, contribute to alterations in fertility and semen quality observed from season to season.

To test this hypothesis, the research team recruited 16 Shetland Pony stallions. Eight were housed indoors with an average temperature of 56.5° F (13.6° C) and eight housed outdoors with an average temperature of 41° F (5.6° C). Both groups of horses were exposed to the same amount of light each day in an attempt to assess the effect of temperature alone.

In terms of semen quality, noteworthy findings were:

  • Circulating testosterone levels underwent seasonal changes but did not differ between the two groups of stallions;
  • Semen volume and total sperm count were influenced by season. Specifically, an increase in semen volume and total sperm count occurred in both groups; however, the increase from winter to spring was more pronounced in the stallions housed outdoors than the group housed indoors;
  • No difference between the two groups in terms of sperm concentration was detected;
  • Similarly, progressive motility of spermatozoa was highest in the spring but no difference in motility was noted between the two groups; and
  • Finally, no difference in either motility or sperm cell integrity was noted between the two groups in semen samples that were either cooled or cryopreserved.

“These results show that ambient temperature apparently has only a minimal effect on semen characteristics, which in turn suggests that season/photoperiod has a greater impact on reproductive parameters than temperature,” explained Kathleen Crandell, Ph.D., a nutrition for Kentucky Equine Research (KER).

The study authors additionally noted that hair coat parameters differed between the stallions. While season impacted the hair coat in both groups, stallions housed indoors with a higher ambient temperature had shorter guard hair, slower hair regrowth with changing seasons, and earlier hair changes than stallions housed outdoors.

“Regardless of how your stallions are ultimately managed, omega-3 fatty acid supplementation using marine-derived sources of DHA and EPA like those found in EO•3 improve various reproductive parameters and semen quality in addition to improving hair coat quality. EO•3 also supports joint health,” reminded Crandell.

*Schmidt, K., K. Deichsel, R.A. de Oliveira, et al. 2017. Effects of environmental temperature and season on hair coat characteristics, physiologic and reproductive parameters in Shetland pony stallions. Theriogenology. 97:170-178.