Gestation length is important for some of the criteria that controls reproductivity in practice. Gestation length in the ewes is variable; additionally the variation in physical signs of imminent parturition makes the prediction of parturition in the ewes particularly diffıcult. The management of high value stock demands the precise prediction of parturition. The inability to accurately predict the timing of parturition incurs extra labour and veterinary costs and higher risks to both dam and lamb. Any factors that may be used to help determine the timing of parturition are, therefore, of considerable interest to the industry (6).
The duration of pregnancy in sheep can vary according to several factors; these include the number of lambs in the conceptus, the sex of the lambs, the sire breed, the breed of ewe and its age (13). Some authors have distinguished certain categories of sheep in terms of the length of their gestation period. These include: the early- maturing improved meat breeds (eg. Southdown, Suffolk, Hampshire, Dorset Horn) with gestation periods varying from 144 to 147 days; the slow-maturing fıne-wool breeds (Merino, Rambouillet) with periods averaging 149-151 days; and crossbred long- wool breeds (Colombia, Corriedale) with periods in the intermediate range (13). Gestation length was longer for triple births (153.7 days) than for twin births (152.8 days), and twins was longer than single lambs (151.6 days) in Konya Merino ewes (19). There is, however, a decrease in gestation length with increasing litter size in Clun Forest ewes; for quadruplet births (144.8 days) it was lower than for triplet births (146.7 days), for triplet births it was lower than for twin births (146.8 days) and single lambs (147.5 days), and for twins it was lower than single lambs (12). it was reported that under a decreasing day length pattern and low temperatures during late pregnancy, gestation length in Finn-cross ewes was shorter than under the opposite environmental conditions (3). This study was carried out to investigate effects of breed, mating season, age of ewe, birth type, sex of lamb and birth weight on gestation length in Hamdani, Red Karaman and Karakul ewes.
Yüzüncü Yıl. Data (n=259 lambings) were collected from 40 Hamdani (2-yr-old=28; 4-yr-old=12), 50 Red Karaman (2-yr-old=14; 4-yr-old=36) and 35 Karakul (2-yr-old=10; 4-yr-old=25) ewes.
Sheep were received concentrate feed (500 g per ewe per day) in addition to grazing on pasture starting from 4 weeks before mating until mating time, concentrate feed (500 g per ewe per day) in addition to ground sainfoin ad libitum at fırst 3.5 months of pregnancy, and concentrate feed (700 g per ewe per day) in addition to ground sainfoin ad libitum for last 1.5 months of pregnancy in the autumn mating season.
Sheep were received concentrate feed (500 g per ewe per day) in addition to grazing on pasture starting from 4 weeks before mating until mating time. The ewes grazed on pasture without any concentrate feed at fırst 3.5 months of pregnancy, and the ewes received concentrate feed (700 g per ewe per day) in addition to ground sainfoin ad libitum for last 1.5 months of pregnancy in the summer mating season.
Sheep were received concentrate feed (500 g per ewe per day) in addition to ground sainfoin ad libitum starting from 4 weeks before mating until fırst month of pregnancy. The ewes were grazed on pasture without any concentrate feed from second months of pregnancy until last 1.5 months of pregnancy, and the ewes received concentrate feed (700 g per ewe per day) in addition to ground sainfoin ad libitum for last 1.5 months of pregnancy in the winter mating season.
Mating and birth dates of ewes were recorded. Furthermore, age of ewe, birth type, sex of lamb and birth weight of lamb were recorded. Gestation length was described as the time period passed between last mating date and parturition of ewes. Data were analyzed using the least squares method (14). The difference between the mean values was determined by Duncan’s test (7). Gestation lengths were analysed by linear models of statistical analysis as follow. For ewe’s gestation length
yijklmno = [1+ b{ + gj + ak + ti + Sm + Wn + eijklmno
Yijkımno is the individual observation,
Hthe expected mean,
bi the effect of birth weight (i: 1.5-2.5, 2.6-3.5, 3.6-4.5, >4.6 kg),
gj the effect of breed (j: Hamdani, Red Karaman and Karakul),
ak the effect of ewe’s age (k: 2 and 4 year),
ti the effect of type of birth (1: single and twin),
sm the effect of sex (m: male and female),
wn the effect of mating season (n: autumn, summer and winter),
eijklmno the random error.

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Least square means, standart errors and signifıcance probabilities for gestation length (day) are presented in Table. Average gestation lengths in Hamdani, Red Karaman and Karakul ewes were 149.77±0.18, 148.76±0.15 and 147.79±0.19 days, respectively. The longest gestation length was observed in Hamdani breed, followed by Red Karaman and Karakul breeds, respectively. The effect of breed on gestation length was signifıcant (P<0.01).
Gestation lengths of mated ewes in different seasons were similar (P>0.05). Gestation lengths of 2-yr-old ewes (148.76±0.17) and 4-yr-old ewes (148.78±0.12) were similar (P>0.05). Gestation length of ewes which gave birth to single lamb (149.36+0.11) was longer than those which gave birth to twin lambs (148.18±0.21). The effect of birth type on gestation length was signifıcant (P<0.01).
Gestation length of ewes giving birth to male lamb (149.17±0.14) were longer than those giving birth to female lamb (148.37±0.13). There was signifıcant difference (P<0.01) in gestation length between ewes which gave birth to male- and female-lambs. Birth weight did have a signifıcant effect (P<0.01) on gestation length. Gestation length increased with increasing birth weight of lambs.
Values in columns with different letters are significantly different (P<0.01). S. E.: Standart hata, C.E.: Etki payı, ns: Önemsiz. Aynı sütunda farklı harf taşıyan ortalama değerler arası farklar önemlidir (P<0.01).


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Discussion
Average gestation lengths in Hamdani, Red Karaman and Karakul ewes were 149.77, 148.76 and 147.79 days, respectively. When the results of this study were compared to the results of other researchers, gestation lengths of Hamdani, Red Karaman and Karakul ewes were shorter than those of Sharka ewes (154 days) (5), White Karaman and Awassi (149.93 and 151.38 days) (18), Konya Merino ( 152.7 days) (19) and Dohne Merino ewes (151.6 days) (25), were longer than those of Prealpes-du-Sud (145.8 days) (2) and Dorper ewes (146.5 days) (15). in the present study, the effect of genotype on gestation length was signifıcant (PO.01). This observation is in general agreement with the results reported in the literatures (4, 18, 20), contrary to the results reported by Gabrilidis (11), Sahani and Chand (21).
The effect of mating season on gestation length was not signifıcant (P>0.05). The effect of mating season on gestation length could not be discussed, because no article has been found on the effect of mating season on gestation length.
Age of ewe did not have a signifıcant effect (P>0.05) on gestation length. This result is in general agreement with the results reported in the literatures (1, 22) and contrary to the results reported by Fernandes and Deshmukh (9) and Gabrilidis (11).
Gestation length of ewes which gave birth to single lamb was longer than those which gave birth to twin lambs. This result was in agreement with the results of Clun Forest (12), Awassi (16), Chios and Awassi sheep (17). However, Akçapınar and Kadak (1), El Karim and Owen (8), Fuentes et al. (10) and Öztürk (18) reported that gestation length of ewes giving birth to twin lambs were longer than those giving birth to single lambs. This observation is in general agreement with the results reported in the literatures (10, 24 ) and contrary to the results reported by Akcapinar and Kadak (1), Shrestha and Heanay (22).
Gestation length of ewes which gave birth to male lamb were longer than those which gave birth to female lamb, which is in agreement with some studies (10, 18, 24). Some researchers reported that gestation length of ewes giving birth to female lamb were longer than those giving birth to male lamb (1, 23).
Gestation length increased with increasing birth weight of lambs. Birth weight did have a significant effect (P<0.01) on gestation length. This result is not in agreement with the result reported by Trimnell et al. (24). These differences among studies could be due to breed and various environmental factors.
In conclusion, gestation length in the breeding flock is the major factor influencing profitability. In order to optimize reproductive efficiency a sheep producer must understand the basic stages of the gestation of a sheep and factors affecting gestation length. Gestation length in Hamdani, Red Karaman and Karakul ewes were affected by breed, sex of lamb, birth type and birth weight of lamb, and was not affected by mating season and age of ewe. There was an increase in gestation length with increasing birth weight of lambs.


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