THE RESPONSE OF EWES FROM 3 LOCAL GREEK BREEDS TO A LONG-DAY SKELETON PHOTOPERIOD DURING THE WINTER

Adult ewes from three local Greek dairy breeds, pregnant from September matings, were kept under natural photoperiod (control group, n=47) or under a long-day treatment; the latter treatment was simulated with exposure to a 1-h-long 300 lux light pulse, 16 to 17 h after an artificial dawn (light-treated group, n=44) over a 3-moperiod (from December 1 to February 29). The weight of the newborn lambs and their daily weight gain during the nursing period (6 to 7 wk) were similar in the two groups. The percentage of ovulating ewes during March and April was low (approximately 20%) for both the control and the light-treated groups. However, the mean date of the onset of the sexual season (first cyclic ovulation and estrus) occurred 1 to 2 wk earlier in the treated than in the control ewes. The fertility of the ewes mated at their second seasonal estrus was high (about 75%) and similar in the two groups. The above results are discussed in connection with the different, and in some cases contradictory, results obtained in other, similar studies. © 1990.