The present study was undertaken to investigate the influence of hCG, administered on the 4^th day following insemination, on serum progesterone levels, pregnancy rates and the duration of the oestrous cycle in the Doğu Anadolu Kırmızısı (DAK) cows.

Fifteen DAK cows aged between 6 and 8 years were used in this study. All animals were synchronised by inject-ing prostaglandin F2 alpha twice at 11 day intervals and the animals were then inseminated. Those cows which exhib-ited regular oestrous cycles were allocated as experimental (n=9) and control (n=6) groups. These two groups received 1500 IU hCG and physiological saline (2 ml), respectively, commencing on the 4^th day following in-semination. Blood samples were obtained from all animals on the days 0 (at insemination), 4, 7, 10, 13, 16, 19 and 21st days following insemination. Serum progesterone levels were determined by using double radioimmunassay method. The pregnancy of cows was determined by ultrasonographic examination on the 45^th day.

In the ultrasonographic examination of the animals on the day 45, 1 control and 7 hCG-injected cows were found to be pregnant. Serum progesterone levels were significantly different between the experimental and control groups on day 13 (p<0.05). The significant differences were also observed when progesterone values on day 19 (p<0.05) and mean progesterone values (p<0.05) of non-pregnant cows in both groups were compared.

In conclusion, we suggest that hCG administration on the 4^th day following insemination increases pregnancy rates, but has no effect on serum progesterone levels and the duration of the oestrous cycle in the DAK cows.