Диагностика на ранната бременност и определяне на броя и пола на плодовете при овце
Early pregnancy diagnosis and fetal number and sex determination in sheep
овце; бременност; диагностика
The sheep breeding is one of the most important branch of animal husbandry in Bulgaria. Increase of sheep population is impossible without introduction of up-to date methods in the reproductive process. Early pregnancy diagnosis is effective method for detection of non-pregnant animals, early embryonic death and some reproductive tract diseases in sheep. It allows planning of animal for replacement, imuuno-prophylactic treatments in pregnant animals and preparation of the flock for future lambing. The fetal number determination is precondition for choice of adequate nutrition and reducing of losses caused by pregnancy toxemia and dystocia. The fetal sex determination has key importance in purebred sheep breeding. The subject of the current thesis is early pregnancy diagnosis and fetal number and sex determination in three sheep breed from different directions - Trakia Merino sheep (wool), Pleven Blackhead sheep (milk) and Ille De France (meat). The investigations were carried out with 1812 sheep, 565 Trakia Merino breed, 717 Pleven Blackhead breed and Ille De France. Early pregnancy diagnosis was performed by blood progesterone concentration measurement and transrectal and transabdominal ultrasound examinations with 5 MHz linear probe until day 50 after artificial insemination. The correct criterions for early pregnancy diagnosis according to the gestational phase were defined. The effects of time for investigation, ultrasound examination approach and sheep age and breed on the parameters (accuracy, sensitivity and specificity) of used method for pregnancy diagnosis were recorded. Fetal number determination was done by ultrasound examination and progesterone level in sheep bearing one or more fetuses was measured. Foetal sex was determined between days 30 and 79 of pregnancy by ultrasound. In addition, correct criterions for fetal sex determination according to the gestational phase and effect of foetal sex on the accuracy of the method were registered. The analysis of results indicated that ultrasound examination is correct method for early pregnancy diagnosis in the used sheep breeds. The positive diagnosis and exclusion of early embryonic death is recommended to be set in observation of enlarged uterine lumen, embryo or foetus with cardiac activity and placentomas. The time for ultrasound investigation and number of fetuses have significant influence (P<0.05) on the parameters of pregnancy diagnosis method. The most appropriate period for foetal number determination and exclusion of partial embryonic death is the time between day 41 and day 50 of pregnancy. Increased accuracy of the ultrasound method is connected with single pregnancy. On day 60 of pregnancy, blood progesterone concentration is lower (P<0.05) in sheep bearing one fetus compared to animals bearing more fetuses. The most appropriate period for foetal sex determination is day 65 of pregnancy. The ultrasound examination is recommended to be done in frontal position of the fetus. The accuracy of used method tended to be increased in male fetuses than females (87% vs. 79%). On the base of the obtained data a few recommendations could be presented: initial ultrasound pregnancy examination in sheep to be made not earlier than 20 days after artificial insemination; a positive diagnosis to be based at least two or more specific criterions for pregnancy; pregnancy detection and foetal number determination by transrectal examination and probe with 5 MHz frequency is recommended until day 40 after insemination, after that a transabdominal approach is more suitable; foetal sex determination to be carried out between days 65 and 72 of pregnancy in frontal or sagittal position of the fetus. The abovementioned investigations provide additional knowledge for application of the modern diagnostic methods in sheep reproduction which could be beneficial to veterinary practice.