| The present experiment was worked on the treatment of postpartum cows, and long term infertility cows as well as early pregnancy diagnosis, and used B-ultrasonography technology, objective to shorten dairy cow calving interval.Experiment 1:In order to understand the effects of LRH-A2 and cloprosterol on shortening calving interval and select the optimum time for LRH-A2 treatment, 50 and 51 postpartum Holstein cows,which the milk yields were 8000kg/305d and 6000kg/305d were randomly divided into the control group, the Groupâ… (2 weeks postpartum), Groupâ…¡(20-40 days postpartum), groupâ…¢(41-60 days postpartum) ,and injected LRH-A2,cloprosterol respectively. 3 cows of each group were selected randomly and observed the changes of ovary pre-injection and post-injection with B-ultrasonography. The results showed that when LRH-A2 was injected at postpartum 2 weeks, it contributed to shortening the calving interval.Experiment 2:Cows with reproduction disease which include endometritis, ovaries cyst, inactive ovaries and infertility postpartum 80d were treated with hormone and antibiotic. The result showed as following : Qinggongye is better for endometritis.; The effect of LRH-A2 on follicle cyst and inactive ovaries is significant ; The effect of PG on corpus luteum cyst is significant ; when cows with follicular were treated with LRH-A2+PG to estrus and injectioned intramuscularly with LRH-A2 again at the time of insemination, the conception rate was improved; The conception rate of cows with corpus luteum was improved when treated with PG+ sodium selenite Vitamin E.Experiment 3:123 cows that unestrus after insemination 40d were diagnosed with B-ultrasonography in early pregnant phase. open cows were treated with hormone according to the condition of uterus and ovary. The results showed that it were early pregnancy diagnosis after insemination 28～35d and treatment of open cows in time that contributed to shortening the calving interval and improved cow's breeding rate.
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