MAINTENANCE OF SPERM PRODUCTION IN BUCKS DURING A 3RD YEAR OF SHORT PHOTOPERIODIC CYCLES

We have previously shown that reproductive seasonality of bucks was pr evented for 2 consecutive years by short photoperiodic cycles. To dete rmine the effect of the length of treatment time on bucks subjected to the same photoperiod conditions, experiments were continued for a thi rd consecutive year on 3 groups of 6 Alpine and Saanen bucks. The cont rol group was kept under natural photoperiodic conditions, while the e xperimental groups were exposed alternately to 1 month of long days an d 1 month of short days (group 2M) or to 2 months of long days and 2 m onths of short days (group, 4M). Prolactin profiles indicated that buc ks from both experimental groups responded adequately to rapid photope riod changes as their plasma pro[actin levels were significantly highe r in long days (mean +/- SEM; 2M: 61.1 +/- 15.9 ng/ml; 4M: 102.2 +/- 1 3.5 ng/ml) than in short days (2M: 35.3 +/- 8.2 ng/ml; 4M: 46.1 +/- 9. 0 ng/ml). Testosterone secretion was also dependent on day length (P < 0.0001), since testosterone concentrations of experimental animals we re higher during long days (2M: 7.0 +/- 0.7 ng/ml; 4M: 10.2 +/- 1.1 ng /ml) than during short days (2M: 4.3 +/- 0.4 ng/ml; 4M: 5.0 +/- 0.9 ng /ml). Furthermore, controls displayed a high level of sexual behavior (always higher than 10%) and the proportion of bucks unable to ejacula te was significantly lower (P < 0.01) than the experimental animals (2 M: 25.6%; 4M: 28.1%). In controls, the testis weights exhibited distin ct seasonal variations, increasing from 120.0 +/- 0.1 g in May to 155. 0 +/- 4.2 g in November, whereas in the experimental animals, the test is weights remained elevated (2M: May = 160.0 +/- 7.3 g, November = 15 1.6 +/- 7.3 g; 4M: May = 155.00 +/- 11.8 g, November = 160.0 +/- 12.2 g). Importantly, the mean total number of spermatozoa per ejaculate th roughout the year was higher (P < 0.05) in experimental animals (2M: 7 .8 +/- 0.5 x 10(9); 4M: 7.8 +/- 0.3 10(9)) than in the controls (5.0 /- 0.2 x 10(9)) and the mean daily sperm output, measured after exhaus tion tests at the end of the photoperiodic treatments, was also higher (P < 0.05) in experimental animals (2M: 3.68 +/- 0.59 x 10(9); 4M: 6. 25 +/- 0.61x 10(9)) than in controls (2.96 +/- 0.36 x 10(9)). It was c oncluded that bucks exposed to rapid alternations between long and sho rt days for a third year maintained a high sperm production and, thus, the seasonality of hypothalamo-pituitary-testis activity was abolishe d.