HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Clay, C. M. Articles by Pickett, B. W. Search for Related Content PubMed PubMed Citation Articles by Clay, C. M. Articles by Pickett, B. W.

Influences of Season and Artificial Photoperiod on Stallions: Testicular Size, Seminal Characteristics and Sexual Behavior^1,2,

Colorado State University, Fort Collins 80523

Abstract

To investigate the influence of daylength on the seasonal reproductive cycle of stallions, 21 stallions were assigned to one of three treatments: 1) control, ambient (natural) photoperiod; 2) S-L, 8 h light and 16 h dark (8:16) for 20 wk beginning July 16, 1982 then 16:8 from December 2, 1982 until March 5, 1984; 3) S-S, 8:16 from July 16, 1982 until March 1984. Temperature was not controlled and was similar for all groups. Total scrotal width (TSW) was measured every 4 wk throughout the experiment. During 10 periods, semen was collected and evaluated every other day for 3 wk and sexual behavior was assessed. The S-L stallions exposed to 16 h light in December had twice as much sperm output in February than in November. Within the February collection period, the sperm output for S-L stallions was greater (P<.05) than that for either control or S-S stallions. The stimulatory effect of the S-L photoperiod also resulted in larger (P<.05) testes and decreased (P<.05) time to ejaculation for S-L stallions in February as compared with either controls or S-S stallions. Despite continued exposure to a 16:8 photoperiod, TSW and sperm output for S-L stallions eventually declined; presumably a consequence of photorefractoriness. The S-S stallions had seasonal cycles coincident with those for control stallions. Based on a sine wave model for TSW and sperm output, stallions in all three groups displayed significant seasonal cycles. We conclude that stallions may possess an endogenous circannual rhythm for which changes in daylength act as a synchronizer or modifier, and that photoperiod can be used to modify the seasonal sexual cycle.

¹ Appreciation is extended to Dr. R. K. Shideler for his attention to the medical needs of the animals in this study, to V. M. Cook and L. Tamlin and to all the numerous graduate and undergraduate students whose assistance made this project possible.

² This research was supported, in part, by grants from the Amer. Quarter Horse Assoc., Amarillo, TX 79168, and the Ed. H. Honnen Scholarship Fund.

³ Reprint requests to: Anim. Reprod. Lab., Colorado State Univ., Ft. Collins, CO 80523.