Breeding data were analysed for 398 gestation periods of 117 purebred Ara'b mares aged 4-19 years which were maintained on Sultansuyu State Farm in Turkey from 1980 to 1907.

Mares were bred in March, April and May, and 249 foaling mares were fred at the foal heat (within 8-12 days). Oestrous detection were made by teasing procedure and clinical examination before being mated 'naturally on the 2nd, 4th and 6th days of oestrus. If a mare was not in oestrus during 60 days it was presumed to be pregnant.

The number of mares at foal heat mating, non foal heat mating and maiden mare mating were 249, 204 and 60 and the respective conception rates were 59.04 %, 60.78 % and 65.00 %. In these three groups, after three cestrous matings conception rates were 75.90 %, 79.90 % and 76.67 %, the rates of mares from which the foal was aborted or dead were 2.41 %, 3.43% and 1.67%, the rates of mares failing to conceive were 24.10%, 20,10 % and 23.33 % and the rates of mares producing a live foal were 73.49 %, 76.47% and 75.00 %, respectively.

The grand total conception rate at first oestrous mating was 60.43 %, after three oestrous mating was 77.58 %. Grand total rates of mares from which the foal was aborted or dead, mares failing to conceive and mares producing a live "foal were 2.78 %, 212.42 % and 74.85 %, for all eight years, respectively.

Last mating day and birtih day were included to gestation length. Gestation length ranged from 314-372 days and averaged 336.45 + 0.45 days. The average gestation length of 145 mares mating at foal heat, 194 mares mating at non foal heat and 45 maiden mares mating were 33.7.95 ± 0.7/2, 33539 ± 0.64 and 336,16 ± 1.16 days, respectively. The differences between average gestation lengths were significant (P< 0.05).