Twenty-four-hour profiles of prolactin and testosterone in ram lambs exposed to skeleton photoperiods consisting of various light pulses

in Reproduction
Authors:
B. D. Schanbacher
Search for other papers by B. D. Schanbacher in
Current site
Google Scholar
PubMed
Close
,
W. Wu
Search for other papers by W. Wu in
Current site
Google Scholar
PubMed
Close
,
J. A. Nienaber
Search for other papers by J. A. Nienaber in
Current site
Google Scholar
PubMed
Close
, and
G. L. Hahn
Search for other papers by G. L. Hahn in
Current site
Google Scholar
PubMed
Close
Free access

Sign up for journal news

Summary. Individual groups of 6 ram lambs were housed within a controlled environment and exposed to one of 6 photoperiod schedules. Groups I and II received 8 (short day) or 16 (long day) h of continuous light, respectively; Groups III, IV and V were exposed to asymmetrical skeleton photoperiods consisting of a main light period of 7 h followed 9 h later by a light pulse of 1 h, 15 min or 1 min duration, respectively, and Group VI was exposed to a symmetrical skeleton photoperiod consisting of two 1-h light pulses positioned 16 h apart. After 4 weeks of treatment serum concentrations of prolactin and testosterone were measured over 24 h. Long-day responses characteristic of the 16L:8D photoperiod (i.e. elevated prolactin and reduced testosterone) were obtained in each of the asymmetric light-pulse treatment groups, but whereas prolactin was elevated over the full 24 h in lambs exposed to 16L:8D, two prominent nocturnal prolactin releases were largely responsible for the high 24-h mean prolactin values in Groups III, IV and V. Reduced serum testosterone in these same groups could not be attributed to a diurnal pattern of secretion but was associated with an overall decrease in testosterone pulse frequency. Prolactin and testosterone levels in Group IV were intermediate between those observed in lambs exposed to 8 or 16 h of light. In summary, light pulses of short duration (1 min) positioned at 17 h after dawn can produce endocrine changes in lambs similar to those observed in lambs exposed to 16 h of continuous light.

 

  • Collapse
  • Expand