ABOLITION OF SEASONAL-VARIATIONS IN SEMEN QUALITY AND MAINTENANCE OF SPERM FERTILIZING ABILITY BY PHOTOPERIODIC CYCLES IN GOAT BUCKS

Goat bucks show large seasonal variations in semen quality mainly influenced by photoperiodic changes. Minimum percentage of motile sperm cells and velocity occur during spring and summer. Three groups of Alpine and Saanen bucks (n = 6 in each group) were used to determine whether rapid alterations between long and short days were able to abolish seasonal variations in semen quality. One group remained in open sheds under natural day length (An) which varied from 16 h light (June) to 8 h light per day (December). The first experimental group (2Mo) was exposed to alternations between 1 month of long days (16L:8D) and 1 month of short days (8L:16D) and the second one (4Mo) to alterations between 2 months of long days (16L:8D) and 2 months of short days (8L:16D), during two consecutive years. All parameters of semen quality before freezing and after thawing varied with time in the three groups (P < 0.05). Interaction between group and time was also detected for five parameters out of six (P < 0.001), indicating that groups varied differently with time. Semen quality in the experimental groups was not affected by prevailing day length. As expected, in group An, the percentage of motile sperm and sperm motility score (0-5) before freezing and after thawing decreased during the non-breeding season (March to August; minimum in August: 37.8% and 2.4 score before freezing) compared to the breeding season (September to February; maximum in January: 66.3% and 3.6 score before freezing). The production of semen doses available for A.I. also decreased during this period. In contrast, in the two experimental groups the decrease in sperm quality during this period was prevented. In these groups, the percentage of motile sperm and sperm motility before freezing and after thawing remained at the same level as observed in group An during the natural breeding season. Abolition of seasonal variation in semen quality led to production of 69.0 and 54.7% more A.I. doses in groups 2Mo and 4Mo than in group An. Sperm fertility in the three groups did not show significant differences (59.4% of kiddings in 1599 goats from 58 flocks). It was concluded that, in goat bucks, alterations between long and short days abolished the seasonal variation in semen quality without altering sperm fertility.