| Summary: | 碩士 === 國立屏東科技大學 === 畜產系 === 94 === High temperature and humidity in hot season（May to Oct.）result in significant heat stress for dairy cattle and thus reduce their reproductive performance. Objectives of these studies were to evaluate the effectiveness of strategies including Heat-Watch monitoring, estrous synchronization and embryo transfer in improving cows’ reproductive performance in Taiwan. Automatic Heat-Watch monitoring system was applied in Experiment 1 to enhance heat detection. Estrus detection results from Heat-Watch were combined with results from ultrasonic scanner for ovary studying. These joined techniques were of benefit that detecting the ovulation timing was helpful in deciding the proper period for artificial insemination (AI) and also increasing the understanding regarding ovary development and heat behavior in hot season. Heat-Watch system was applied to 37 head of cows and 10 head of heifers. Results from cows showed that there was averaged 6.5 5.6 times of steady mounting in each cycle with duration of 2.3 0.5 seconds per mounting, and standing heat could last for 6.2 3.2 h. For heifers, three traits were averaged 10.4 7.6 times, 2.9 0.7 seconds and 10.7 5.2 h, respectively. Data from confirmed pregnant cows indicated that interval between the first steady mounting and proper AI timing was 17.6 ± 6.2 h for cows and 11.8 ± 3.6 h for heifers. In Experiment 2, exogenous PGF2α or GnRH + PGF2α were administered to synchronize estrous cycle. It was expected to concentrate the heat occurrence and thus promote heat detection rate and the efficiency of reproductive management. In hot season, exogenous hormone treatment could promote 14.2% of pregnancy rate of cows. Pregnancy rates of control group and treated group were 13.6% (6/44) and 27.8% (20/72), respectively. Effect of exogenous hormone treatment did not showed in heifers, pregnancy rates were 44.9% (22/49) for control and 48.7% (19/39) for PGF2α group. For both cattle, pregnancy rates did not differ significantly. In Experiment 3, super-ovulation and embryo flushing and collecting were proceded in cool season and transferred in hot season to skip the heat-sensitive period, seven days after fertilization, of embryo. There were 141 transferable embryos collected and among these 59 embryos were transferred. A total of 24 head of cattle were confirmed to be pregnant by rectal palpation and reach the 40.7% of pregnancy rate (24/59). During cool season (from Jan. to Apr.), 11 head of cattle were pregnant among 28 transferred cases. Pregnancy rate was 39.3% (11/28). During hot season (from May to Oct.), 13 head of cattle were pregnant among 31 transferred cases. Pregnancy rate reaching the high 41.9% (13/31) level implicated that embryo transfer is an effective strategy. In summary, results from these studies indicated that Heat-Watch monitoring, estrous synchronization and embryo transfer could improve dairy cows’ reproductive performance during hot season in Taiwan.
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