[Seasonal variation in the testis diameter and sperm morphology in the Vendean ram and Texel ram]

Nineteen Vendean (V) rams (7 yearlings about 15 months old and 12 adults of greater than 2 years) and 13 Texel (T) adult (greater than 2 years) rams were controlled for body weight (BW), testis diameter (TD) and sperm morphology for two consecutive years (1982 and 1983) from February to June (T) or July (V) and from September to November the first year, from February to June and from September to October the second year. BW was recorded every month. TD was measured once weekly using a caliper. The percentage of abnormal spermatozoa (MA) was determined on each ejaculate (1 ej/ram/week) as described previously (Colas, 1980). BW increased rapidly (P less than 0.01) in the T rams the first 4 months and did not augment significantly any more afterwards. In the V breed, no significant variations appeared at any time of the experiment, except in the last month when BW decreased (P less than 0.05). However, in the yearlings (V), there was considerable body growth between February and October 1982 but no significant growth afterwards. In the adults, no statistical variations occurred at any time of the experimental period. TD varied greatly during the year in the V rams. During both years, it was minimal in May (59.0 +/- 5.7 m/m in 1982; 58.1 +/- 4.4 m/m in 1983); in September it was already regressing. There were also large seasonal variations in the TD profile of the T breed but its curve was different from one year to another: the mean value was minimal in February 1982 59.5 +/- 6.0 m/m) and from February (67.5 +/- 4.4 m/m) to May (68.6 +/- 5.0 m/m 1983. In both breeds, testicular growth always started in June, i.e. during the long days, whatever the year. The importance of the variations and their time of onset during the year suggest that both breeds were very sensitive to photoperiod. These results also permit a generalization of the idea that testicular activity in male sheep recommences in the long days. Both breeds showed large individual variations between the minimal values recorded in spring and the highest ones measured in September (2.7 to 78.0% and 2 to 100%, respectively, for V and T rams in 1982; 5.5 to 100% and 14 to 84% in 1983). On the whole, MA were more frequent from February to June than from September to October or November in both breeds. In the V breed, MA were highest in April (35.1% in 1982, 33.1% in 1983).(ABSTRACT TRUNCATED AT 400 WORDS)