MATERIALS and METHODS In the present study, 29 Holstein-Friesian cows were used in the postpartum day. The animals were divided into two groups as β-carotene uninjected (β-Car (-); n=15) and β-carotene injected (β-Car (+); n=14). All cows were synchronized with single dose of PGF 2  (Enzaprost ® ; 5ml/cow, im, Ceva-Dif) and double artificial inseminations were performed at the time of 48 and 72 hours after synchronization. Last insemination was accepted as a day 0. GnRH (Receptal ® ; 2.5ml/cow, im, Intervet) was injected in both groups at the days of synchronization (-3), 7 and 17. The injections of β- Car (Carofertin ® ; 20ml/cow, im, Alvetra  Werfft AG) were performed only β-Car (+) group unlike β-Car (-) group at the day -3, 7 and 17. Images of corpus luteum (CL) and blood samples were collected to measure the luteal size (LS), luteal blood flow (LBF) and blood serum β-Car and progesterone concentrations at the days -3, 7, 10, 17, 27 and 37. The CL was displayed with color-doppler ultrasonography (LOGIQ BookXP, Germany) with a 10.0 MHz linear-array transducer and at least six images were taken in each examination. In order to minimize variations between recordings, the settings for the Power Doppler system were fixed and the same settings were used in all examinations. The images were taken when the largest CL was displayed from the route of transducer latero- medial and dorso-ventral. After the transfer of these images as a DICOM format to the computer, four images with the maximum number of color pixels within the sectional planes near the maximum diameter of the CL were selected for calculating the mean blood flow. The colored area was measured using a software (Pixel Flux™, Version 1, Chameleon Software, Leipzig, Germany) and used as a semi-quantitative parameter for LBF. Data were analyzed (Descriptive Statistic, Mann Whitney U-Test, Repeated Measures Define Factors-Test) using SPSS 16.0 (SPSS Inc., Chicago, USA). CONCLUSION Injection of β-Car in addition to the GnRH injections in early pregnancy days after inseminations LS, LBF and blood serum β-Car concentrations have significantly increased compared to β-Car(-) group. It was thought that this resulted in higher pregnancy rate in β-Car(+) group.CONCLUSION There was significant increase in β-Car levels after injection of β-Car in β-Car(+) group (Graphic 1). After inseminations, it was determined that there was significant difference between β-Car(-) and β-Car(+) groups at all of the pregnancy days (except day 17) (P 0.05). There was a positive correlation (r=0.882; P<0.01) between LS and serum β-Car levels in β-Car(+) group (Table 2). RESULTS Graphic 1. Changes of the blood serum β-car concentrations in groups. INTRODUCTION β-carotene functions independently of vitamin A in regulation of ovarian functions (Lotthammer, 1999). Supplementation to the ration or injection of β-carotene increase plasma concentration of β- carotene (Arechiga et al., 1998; Wang et al., 1988; Sales, 2007). β-carotene also has a positive effect on the size of corpus luteum (Aslan et al., 1998; Agaoglu et al., 2009). The stimulation of the gene Connexin-43 and formation of Gap-junction by β-carotene shows its effect positive on functions of the corpus luteum (Arıkan and Rodway, 2000; Arıkan et al., 2002). Angio mod of the color Doppler ultrasonography is a non-invasive and safe imaging method to display blood viscosity of corpus luteum (Myamoto et al., 2005; Honnes et al., 2009). The aim of the present study was to determine the effect of administration of GnRH or GnRH+ β-carotene combinations on Luteal size (LS) and Luteal Blood Flow (LBF) in pregnant and non-pregnant cows. P*<0.05; P**<0.01 β-car (-) =P*<0.05; P**<0.01 β-car (+)=P*<0.05; P**<0.01 P*<0.05; P**<0.01 β-car (-) =a*:b*=P<0.05; b*:c*=P<0.05; a:b:c P**<0.01 β-car (+)=a:b:c=P<0.05; a:b:c:d=P<0.01 P*<0.05; P**<0.01 The mean size of CL at day 17 was determined significantly different in day 17 from other days in β-Car(-) group (P**<0.01; P*<0.05). On the other hand, size of CL at days 10, 17 and 37 was found significantly bigger than days 0 and 37 in β-Car(+) group (P**<0.01; P**<0.05) (Graphic 3). CL size at days 27 (P*<0.05) and 37 (P**<0.01) in β- Car(+) group was found to be bigger than β-Car(-) group at same days (Graphic 4). A gradually increase of luteal blood flow was detected in β-Car(+) group from day 7 (except day 37) (P<0.01). In β-Car(-) group, there was an increase in day 10 (P<0.01), a stable level in following days and no significant increase between days 10 and 37 (Graphic 5). As a result of β-Car injections, LBF in β-Car(+) group at days 7 and 27 was determined significantly higher than β-Car(-) group (P*<0.01; P**<0.01) (Graphic 6). The pregnancy rate was found to be higher in β-Car(+) group (71.4%) than in β-Car(-) group (53.3%). Graphic 2. Comparisons of blood serum β-car concentrations between groups. Graphic 3. Changes of the CL size during early pregnancy in groups. Graphic 4. Comparisons of CL size between groups during pregnancy. Graphic 5. Luteal blood flow values between day 7 and 37 of pregnancy Graphic 6. Statistical difference of luteal blood flow between day 7 and 37 of pregnancy. Table 2. Correlation ( R 2 ) between LS and blood serum β-car concentrations in groups at day -3 and 37. Table 1. Study Dizayn Groups DAYS Synchronization Inseminations βC-(n=15) : PGF 2  GnRH GnRH GnRH GnRH βC+(n=15): +βC +βC +βC +βC: days of β-car injections Groups Correlation R 2 P βC (-) CL size / Ser β-Car levels P>0.05 βC (+) CL size / Ser β-Car levels P<0.01