| Summary: | 碩士 === 東海大學 === 畜產與生物科技學系 === 95 === Reduce calving intervals and increase production life of dairy cattle through endocrine regulating of the ovarian function
Reproductive management is very important for the dairy farm business. Effective management can hasten the recovery of postpartum ovarian function and improve the profit in dairy business. The purpose of this study was to investigate the relationship among various postpartum production traits , and to regulate the ovarian function to reduce the calving interval by using exogeneous hormone, hence to
increase the lifespan of dairy cattle.
Experiment 1 was conducted to observe the relationship among various blood constituents and production profiles. From calving to 45 days postpartum, five primiparous and four multiparous lactating dairy cows were used to measure body condition score(BCS)、dry matter intake(DMI)、and BW on a weekly basis；Milk were collected twice a week and milk constituents were analyzed accordingly；Blood were collected twice a week and serum were harvested for progesterone(P4)、glucose、insulin、and cholesterol analysis. The results showed that DMI、energy balance(EB)、milk yield(MY)、serum glucose、insulin、and cholesterol were starting to increase from week2 or week3 postpartum. BW was decreased after calving until week 4 postpartum. And then the lost BW was gradually recovered until week 7 postpartum. BCS was decreased from calving to week 7 postpartum.
Experiment 2 was conducted to study the effects of various systematic breeding programs on reproductive performance of postpartum dairy cattle. The Ovsynch treatment group (n=11) received an injection (100μg) of GnRH at a random stage of estrus cycle , followed 7days later by an injection of 25 mg PGF2α and a second injection of GnRH (100μg) 2 days later .Cows were inseminated at a fix time 24h after final GnRH of Ovsynch. Pregnancy diagnosis was performed 35d later by palpation per rectum of uterine contents. The Presynch treatment group(n=10) started at d24 postpartum, and two PGF2α at a 14 d interval were used to synchronize the estrus , then the Ovsynch program would be followed 12 days later. The initial step of the Resynch program(n=10) was identical to the Presynch program. After TAI, the CIDR driver was inserted and a o.6mg E2 injection was performed 13 days later. The CIDR driver was removed 7 days later and a second E2(0.6mg) injection was performed 24 hours later preparing to detect estrus and AI in 24 hours.
Presynch and Resynch groups has a better synchronization rate (P<0.05) than the Ovsynch group. Presynch protocol has higher incidence of ovulation (90% vs. 45.5%, P<0.05)、better conception rate (50% vs. 9.1%, P<0.05), and need less service per conception than Ovsynch treated cows.
In conclusion, dairy cows after calving that increase DMI can decrease negative energy balance and resumption of ovarian cyclicity postpartum. And presynchronization before treated cows with Ovsynch protocol has the potential to enhance reproductive efficiency of dairy cattle.
Key word：dairy cattle、reproductive efficiency、synchronization、Ovsynch、Presynch、Resynch
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