| Donkey industry is developing vigorously in China,but the production techniques of jennies are backward,and the greatest problem is the low fertility of jennies.In this study,Dezhou donkeys which were fed intensively were chosen for the experimental animals to establish techniques in regulating estrus and ovulation and to explore the relationship between the gestation length with the time of conception and fetal sex.In order to provide scientific theoretical guidance for the production and reproduction of donkey industry.The research was divided into four parts:(1)The effect of prostaglandin F2a analogue treatment on the estrus cycle of the jennies:intramuscular injection of 0.4 mg of cloprostenol on the 3rd day(D3),the 5th day(D5)and the 7th(D7)day after ovulation;different doses of cloprostenol(0.2 mg,0.4 mg,0.6 mg)were intramuscularly injected on the 5th day after ovulation of the jennies,and the ovaries and uterus were examined by rectal ultrasound.The corpus luteum and follicular morphology and ovulation interval were compared among treatments.(2)The effect of GnRH analogue treatment on ovulation of jennies:24 hours after intramuscular injection of GnRH analogue 1.6 mg,the follicular development status was detected by rectal ultrasound every 2 h.(3)The gestation changes in jennies during one year:Based on the field data from the National Black Donkey Beeding Center of Dong E E Jiao Group,the influences of the conception time and fetal sex on gestation length were investigated.(4)The effects of prostaglandin F2a analogues administration on estrous synchronization:the jennies were divided into 6 groups:Group A(two consecutive injections of cloprostenol+two consecutive injections of cloprostenol＋GnRH analogue);Group B(cloprostenol+cloprostenol+GnRH analogue);Group C(LUTALYSE(?)+LUTALYSE(?)+GnRH analogue);Group D(cloprostenol+LUTALYSE(?)+cloprostenol+LUTALYSE(?)+GnRH analogue);Group E(two consecutive injections of LUTALYSE(?)+two consecutive injections of LUTALYSE(?)+GnRH analogue)and control group,the synchronization,ovulation and pregnancy rates were compared among different groups.The results demonstrated that:(1)cloprostenol could effectively cause luteolysis and shorten the ovulation interval of the jennies.The interval from drug treatment to luteolysis in the D3 group was 2.93±1.52 d,which was not significantly different from the D5 group(2.33±1.52 d)and the D7 group(2.36±1.57 d)(P>0.05).However,the ovulation interval in the D3 group was 11.32±2.67 d,which was significantly shorter than the D5 group(13.33±1.63 d)and the D7 group(13.31±2.60 d)(0.01<P<0.05),while the ovulation interval was not significantly different between the D5 and D7 groups(P>0.05).Nevertheless,the difference between all treatment groups and the control group(22.76±1.16 d)was extremely significant(P<0.01).The ovulation rates(D3:97.7%;D5:93.3%;D7:90.0%;the control group:97.7%)were not different among groups(P>0.05).The follicular diameters at ovulation in the treatment groups were significantly smaller than that of the control group(D3:35.75±2.87 mm;D5:35.93±3.17 mm;D7:36.33±3.27 mm vs 36.23±3.49 mm)(0.01<P<0.05).After treatments with different doses of cloprostenol on the 5th day after ovulation,the luteolysis rate in the 0.2 mg group was 90.0%within 72 hours,93.3%in the 0.4 mg group,and 90.0%in the 0.6 mg group.The difference was not significant aomong the groups(0.01<P<0.05),and luteal phases and ovulation rates were not deffernet among the groups(P>0.05).(2)The ovulation rate was 78.95%at 32-48 h after injection of GnRH analogues,and 36-44 h was the most concentrated period of ovulation.(3)Among the five protocols,the estrous synchronization rates in Group B,Group D,and Group E were significantly higher than the control group(46.4%,41.7%,50%vs 25%,0.01<P<0.05),but the ovulation rates were not different(92.3%,90.0%,90.0%vs 87.5%,P>0.05).The pregnancy rates in the Group B and the Group D were not significantly different from that of the Group control(33.3%,33.3%vs 28.6%,0.01<P<0.05),but the pregnancy rate in the Group E was(63.2%)was significantly higher than the control group(P<0.01).(4)The gestation length of the jennies was related to the month of conception.The genstation lengths of the jennnies which were concepted from February to October gradually declined,and the shortest was in July,which was 356.61±15.38 d.The gestation lengths of more than 60%jennies were 351 to 370 d,and the average foaling interval was 411.02±48.96 d.The rate of the jennies with foaling interval more than 410 d was 33.33%,and with the interval≤365 d was only 3.70%.Conclusion:The ovulation interval was reduced to nearly the half time of the normal estrous cycle in the jennies intramuscularly injected by 0.4 mg cloprostenol on day 3 after the last ovulation.Intramuscular injection of 1.6 mg GnRH analogue could effectively control the time of ovulation.The four-injection protocol of LUTALYSE(?)could effectively promote the estrous synchronization rate of the jennise with higher pregnancy rate.The conception time affected the jenny gestation length,and the jennies concepted in July to october had the shortest gestation length. |
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