[Influence of the photoperiod on the production and fecundity of spermatozoa in the adult Ile-de-France ram].

Two groups, A and B, of 5 adult Ile-de-France rams each of the same age were exposed for 52 weeks (October 1975 to October 1976) to an artificial light regime reproducing natural variations of daylength (DL). In group A, DL increased from 8 to 16 h during the first 26 weeks and then decreased. In group B, DL varied in an opposite manner. Light intensity was constant (300 lux/m2) and ambient temperature was controlled (20 +/- 4 degrees C). The rams were collected using an artificial vagina twice weekly (2 X 2 ejaculates/male/week) during the whole experimental period (EP). The volume and concentration of each ejaculate were recorded. The pH of the raw semen was also measured on the first ejaculate once a week or every two weeks, according to material possibilities. The unselected ejaculates of all rams were used for artificial insemination (AI) on the same days in the same flocks between January and October 1976. AI (980 ewes) was always carried out after oestrus synchronization (FGA + PMSG). Amongst these ejaculates, some (3 ejaculates/male/group/period) could be used for both in vitro (pH) and in vivo (AI) measurements: - Weekly sperm production (SP) varied in an opposite manner in both groups during the whole EP. In group A, minimal (10.6 +/- 4.0.10(9) and maximal (25.5 +/- 5.1.10(9] levels were reached from weeks 12 to 28 and weeks 38 to 52, respectively. In group B, SP was maximal (21.8 +/- 2.3.10(9] from weeks 9 to 24 and minimal (12.7 +/- 5.2.10(9] from weeks 36 to 49. The differences between rams were significant within periods of high and low production. - The sperm pH was somewhat higher in both groups when DL increased and vice-versa. Fertility after AI was higher with rams exposed to short days than with rams exposed to long days (65.7 vs 56.7%; P less than 0.01). The season of AI had no effect on mean fertility (61.0 vs 62.3% for ewes inseminated from January to June and from July to October, respectively), whatever the DL. No correlation was found between the pH of the sperm and its fertilizing ability. From January to April, a highly significant correlation existed between fertility and prolificacy in the 10 rams (r = + 0.607). These results show that photoperiodism has an important effect on both ejaculated sperm production and fertility in rams.(ABSTRACT TRUNCATED AT 400 WORDS)