Seasonal variation in semen characteristics of Chios and Friesian rams in Greece.

Five Chios and five Friesian rams were used to study the effect of season on semen production. Semen samples were collected with an artificial vagina. In spite of the large variation of most of the semen characteristics among rams of the two breeds, seasonal variation in semen quantity (volume, concentration and total number of spermatozoa per ejaculate) and quality (percentage of motile spermatozoa, sperm progressive motility and percentage of abnormal spermatozoa) were significant (P<0.05). The best semen was produced mainly during autumn and the worst during spring (semen volume: 1.47ml in Chios and 1.48ml in Friesian rams versus 1.24ml in Chios and 1.07ml in Friesian rams; percentage of abnormal sperm: 5.66% in Chios and 5.42% in Friesian rams versus 8.22% in Chios and 7.75% in Friesian rams; total sperm/ejaculate (x10(9)): 7.05 in Chios and 6.74 in Friesian rams versus 4.09 in Chios and 4.05 in Friesian rams). The magnitude of these seasonal effects was not sufficient to prevent rams from being used for breeding throughout the year. However, the existence of differences among rams within each breed in semen quality and quantity makes it necessary to perform a semen evaluation on individual basis in order to select the best males before they are used for breeding.