[Seasonal variations of sperm quality in adult Ile-de-France rams. II. Fertilizing ability and its relation to qualitative criteria in vitro].

Six adult Ile-de-France rams of different origins, registered in a Flock book, were used in AI for three consecutive years on the same flock (IF) in March-April and in September. The animals (males and females) were always kept in a sheep-fold (natural daylight conditions). They received the same feed throughout the whole experiment. Using the unselected ejaculate(s) of each ram (1 dose diluted sperm/female), artificial inseminations were carried out after oestrus synchronization (FGA + PMSG). Massal motility, percentage of nigrosin-eosin-stained spermatozoa and percentage of morphologically abnormal sperm were determined (150 cells/smear) on each ejaculate (or pooled ejaculates of each ram) used for insemination. 1.--In the spring, sperm fertility was strongly diminished (47.1 vs 68.4 p. 100 LR; P less than 0.01, respectively, in spring and autumn), and the differences between the rams were significant (31.7 to 70.3 p. 100; 0.01 less than P less than 0.02 in spring vs 60.0 to 80.0; P greater than 0.05 in autumn). 2.--Fertilizing ability was related neither to massal motility nor to the proportion of stained cells, although, on the whole, the latter was somewhat higher in spring than in autumn. In the spring, there was a close relationship between the fertility of the ejaculate and its proportion of abnormalities (r = -0.83; P less than 0.01). Fertility was also related to the percentage of abnormal heads (r = -0.59; P less than 0.05). In autumn, when the proportion of total abnormalities was much lower and almost exclusively made up of slight tail damages, this relationship disappeared. Morphological examination of the semen is thus a good fertility test. These results show the importance of the ram in successful breeding in an anoestrous period. Morphological test in the spring must be used to detect those males which are most affected by increasing daylight since, at that time (March-April), a ram maintains nearly the same morphological profile from one year to the next (Colas, 1980).