The Sahiwal cow is among one of the well-known dairy breed of zebu (humped) cattle, representing Bos indicus. Information on reproductive aspects is lacking in this breed. Therefore, the intentions of the first experiment was to determine the variations in flow of blood of the uterine artery (UA) based on RI and PI using color-Doppler ultrasonography, during the entire estrous cycle in Sahiwal cattle. Additionally, we characterized the ovarian follicular and luteal dynamics, and the correlation of uterine blood flow, with P4 concentrations in systemic blood. Nine (n = 9), adult, healthy, cycling, lactating Sahiwal cows were registered in the study at their spontaneous estrous. On subsequent estrus, all cows were subjected to AI twelve hours after the onset of standing heat with semen that was freeze, and pregnancy was detected on day thirty post AI. Each cow examined transrectally with B-mode and color-Doppler ultrasound on alternate days throughout the estrous cycle by the same operator. For B-mode, comprehensive pictures of the ovaries were drawn to measure the quantity, diameter, and comparative position of the follicle and CL. The day on which signs of estrus and dominant ovulatory follicle observed was carefully chosen as -1 Day, whereas the day on which dominant follicle (DF) vanish referred as Day 0. Doppler measurements were determined from flow of blood in both the left and right uterine arteries. The analysis was based on Doppler spectrum. The RI and PI were measured to reflect changes in blood flow. RI and PI were calculated from the built-in caliper for measures of blood flow parameters, which were displayed on monitor. Values were recorded when minimum three analogous and uninterrupted waveforms were noted, and three recordings of each day of each side were averaged. Mean RI readings were significantly higher (P < 0.05) at Day -1 (estrus) compared to Day 0 (ovulation). Similarly, mean RI values remained lower (P < 0.05) at Day -1 and Day 0 as compared to remaining days of estrous cycle. We observed a robust outcome of cattle and the days of entire heat cycle (P < 0.05) on RI readings but their interaction was not significant. Mean PI ix reading between -1 Day (estrus) and Day 0 (ovulation) did not differ (P > 0.05) and remained lower. Mean PI value was higher on Day 10 than on Day -1 and Day 0 (P < 0.05). We observed a robust effect of cattle and days of the entire heat cycle (P < 0.05) on PI readings but their interaction was not significant. Concentrations of P4 were greater on Day 12 (6.4 ± 1.0 ng/mL) and then started decreasing on Day 14 (5.0 ± 1.01 ng/mL) until reaching nadir. It is concluded that RI of uterine arteries, as a measure of blood flow, is considerably lower at estrus and ovulation, than during diestrus, whereas PI is substantially elevated during diestrus compared to heat and ovulation in Sahiwal cattle. The objectives of the 2nd study were to determine if there are changes in LS, progesterone (P4), and LBF between pregnant and non-pregnant Bos indicus dairy cattles during the first three weeks after insemination and if these parameters are related to each other. For this, Sahiwal cows (n = 13) of mixed parity (1 - 3) that were healthy, regularly cycling, and lactating, and of 430 ± 18 kg (mean ± SD) body weight were enrolled for the study. All cows were inseminated using frozen thawed semen 12 h after the start of standing estrus. B-mode ultrasonography was performed repeatedly with a 12 h interval to confirm the absence of POF (ovulation), and this day was referred to as Day 0 of the estrous cycle. All inseminated cows were retrospectively categorized as pregnant or nonpregnant. In order to compare the LS and LBF after AI, brightness mode and color-Doppler ultrasonography of the ovaries were performed on Days 4, 5, 6, 7 (first week); 8, 10, 12, 14, (second week); and 16, 17, 18, 19, 20, 21 (third week) in pregnant and nonpregnant cows. During the first and third weeks, ultrasonography was performed daily, while during the second week, cows were examined on alternate days. Thus, each cow had the ovaries ultrasound-mapped fourteen times, resulting in a total of 182 recordings from all cows. The stored images were then subjected to offline analysis using computer assisted image analysis software, x Image J (National Health Institute, Bethesda, MD, USA). In order to minimize the chances of error, mean values of the three images were recorded during each examination for both LS and LBF. Results revealed that the mean LS increased (P < 0.05) from Day 4 (0.9 cm2) to Day 7 (1.3 cm2) indicating the growth of luteal tissue during the first week. However, the average LS did not vary between Day 4 (first week) and Day 19 (third week). The P4 rose (P < 0.05) from Day 4 (1.7 ng/mL to Day 7 (3.0 ng/mL) during the first week, and increased (P < 0.05) further from Day 8 (3.9 ng/mL) to Day 14 (5.8 ng/mL). The LBF increased (P < 0.05) on Day 4 (0.3 cm2) to Day 7 (0.7 cm2), indicating a two-fold rise within 3 days of the first week. During the third week, LBF declined (P < 0.05) from 0.8 cm2 (Day17) to 0.2 cm2 (Day 21) in nonpregnant cows. The mean LS increased (P < 0.05) on Day 4 (1.0 cm2) to Day 7 (1.8 cm2) during the first week. In the following days, LS amplified (P < 0.05) from 1.9 cm2 (Day 8) to 2.8 cm2 (Day 21), indicating a consistent increase in luteal tissue during the first three weeks of pregnancy. The P4 showed a rise (P < 0.05) on Day 4 (1.4 ng/mL) Day 7 (2.6 ng/mL) and from 2.9 ng/mL (Day 8) to 8.4 ng/mL (Day 21). The LBF increased (P < 0.05) more than double from Day 4 (0.4 cm2) to Day 7 (0.9 cm2), as well as from Day 8 (1.0 cm2) to Day 21 (2.4 cm2) in pregnant cows. In conclusion, the present study has provided new information about relationships between LS, P4, and LBF, and indicated that LBF is a more sensitive parameter than LS and P4 to detect the differences of luteal function during the 1st three (3) weeks post AI in pregnant and nonpregnant Bos indicus dairy cattles. Furthermore, this approach could be effectively used to decrease the re-insemination interval, number of days open, and calving interval for the optimization of reproductive management in dairy cows. The comprehensive objectives of these studies are to make advancements in estrus and ovulation synchronization, re-synchronization, decreasing insemination and calving interval, early detection of pregnancy and fetal loss, and minimizing the pathological conditions of the uterus and ovary by using this novel and non-invasive technique.