Ovarian and thyroid activity of the Lacaune ewes breed during the year in Greece

Published: Dec 19, 2017
Sheep breeding season Lacaune persistent corpus luteum.

Ovarian and thyroid activity was studied in 10 ewes of Lacuane breed during one year. Ewes were maintained separately from rams and were fed. The aim of the study was to determine the duration of the anestrus period. Blood samples were collected weekly for the determination of progesterone levels. Thyroxine levels were also determined. Progesterone concentrations > 1 ng/ml were considered as indicative of ovulation, whereas levels between 0.5-0.9 ng/ml as indicative of follicle luteinizations or short lived corpus luteum. Two ewes showed persistent corpus luteum which regressed in deep anestrus period. The first ovulation occurred on 18th August ±10 days. The duration of the breeding season (the interval from the first to the last ovulation) was estimated to be 158 ± 8 days and the number of ovarian cycles during this period was 9.0 ± 0.6 per ewe. A significant correlation was observed between the time of the last ovulation and the duration of the breeding season, (Y=l4l.4+0.96X, r2 = 0.71, P<0.01). Serum thyroxine levels in every fifteen days samples fluctuate from 47 ± 4 during the first half of August to 82 ± 5 during the second half of December. Mean thyroxine levels during the time of increasing daylength (23rd December to 22nd  June) were 71.2 ± 2 ng/ml and during that of decreasing daylength (23rd June to 22nd December) 59.4 ± 3 ng/ml, (p<0.001). In conclusion, this study showed that the ewes of the Lacaune breed exhibit a long anestrous period compared to the indigenous Greek breeds. Hormonal control of estrus is necessary for the out-of season lambing. Finally, thyroid function shows a significant seasonality, as has been demonstrated in all other breeds of sheep studied so far.

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