Exposure of NZ Wiltshire sheep to a long-day photoperiod during late winter/spring has previously been shown to alter wool follicle growth patterns. The present experiment was undertaken to evaluate the plasma prolactin and wool follicle response to treatment with either 1, 2 or 3 months of long days. Four groups of six, NZ Wiltshire ewes were subjected to long-day photoperiod (16L:8D) for 1 month (LD1), 2 months (LD2), 3 months (LD3) or natural photoperiod (control), commencing on the 3 August, after which they were released from light treatment into natural (indoor) spring daylength. Weekly jugular blood samples were assayed for prolactin (PRL) and skin biopsies were histologically assessed for wool follicle activity. Circulating PRL concentrations were low in all treated and control sheep at the start of the experiment (19 ± 2 ng/ml). In treated sheep mean PRL concentration increased (P<0.05) above control levels (8 ± 1 ng/ml) within 1 week after exposure to long days (52 ± 4, 51 ± 5 and 55 ± 2 ng/ml for LD1, LD2 and LD3, respectively). PRL concentrations remained significantly higher than controls (P<0.05) for the duration of each treatment reaching maxima of 148 ± 27 ng/ml, 180 ± 43 ng/ml, and 199 ± 33 ng/ml for LD1, LD2 and LD3 respectively. In LD2 and LD3 treatments, PRL concentrations declined to control levels by 3 and 2 weeks after treatment had ceased, respectively, but in the LD1 treatment PRL remained significantly above (P<0.05) control levels until between 2 and 3 months after treatment. Primary follicle activity (PFA) decreased in response to long-day treatment (P<0.01) reaching minima of 47 ± 9%, 36 ± 6%, and 33 ± 11% in LD1, LD2, LD3 sheep, respectively. Secondary follicle activity (SFA) responses were most marked in the LD2 and LD3 treatments where they fell below (P<0.05) control levels reaching minima at 2 months into treatment (66 ± 15% and 58 ± 13% for LD2 and LD3, respectively). Both PFA and SFA increased to over 90%, within 1 month after release into natural light, in all treatments groups (except PFA for the LD1 group which took 2 months after release to reach over 90%). In support of previously reported trials an increasing level of plasma PRL was followed by a decline in follicle activity. The optimal time frame to achieve an effective synchronised follicle regression was between 2 and 3 months of long- day treatment. The long-day treatment system produced a complete follicle growth cycle in temporal synchrony and is therefore a potential model for the investigation of structural and biochemical processes surrounding transitions between active and resting stages of fibre growth.

AJ, Craven, AL Parry, JE Wildermoth, and AJ Pearson

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 135-138, 1994
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