عنوان مقاله [English]
Introduction As pregnancy progresses, nutrient requirements of fetus and thereby ewe increases and some changes in the levels of blood metabolites including glucose, cholesterol and total protein may occur. During gestation, maternal tissues contribute to supplying energy that required for fetus resulting in changes of ewe blood metabolites; however other factors such as breed, age, feeding type of ewes during gestation and season may influence them. The study of blood metabolic changes in different phases of reproductive cycle can be helpful in detecting abnormal situations of ewes and preventing of metabolic disorders such as pregnancy toxemia and fatty liver syndrome. There is little information about the effect of different genotypes on blood metabolites and the occurrence of metabolic disorders in late pregnancy. Therefore the aim of the present study was to determine changes in blood metabolites of purebred Ghezel and ArkharMerino× Ghezel crossbred ewes during late pregnancy and effect of crossbreeding of Iranian purebred sheep with Merino sheep on metabolite level changes in these two groups of sheep and study of susceptibility to metabolic disease in late pregnancy.
Materials and Methods In the present study, fifty five pregnant Ghezel ewes (36 singles and 15 twins) and 34 pregnant crossbred ewes (20 singles and 14 twins) were used. Estrus synchronization of all ewes was done using CIDR. CIDR were removed 14 days later and all ewes were injected PMSG intramuscularly and then mated with rams. All of the ewes were grazing in the pasture during pregnancy, but in the last two months of pregnancy, feeding of ewes was manually. Blood samples were collected by vacuum tubes during four hours after feeding from the jugular vein of ewes on 15 days prior to mating period and on days 90, 120 and 140 of the pregnancy. Blood samples were centrifuged with 4000 rpm for 12 minutes to extract blood serum and then sera were frozen in -20oC until further analysis of metabolites. Measurement of blood metabolites, including total protein, calcium, glucose, cholesterol, blood urea nitrogen and albumin was done by spectrophotometer set. SAS software (2003) was used for statistical analysis. Mixed procedure of SAS software was used for statistical analysis and Tukey- Kramer test was applied for comparison of means. T-test was used for comparison of blood metabolites between ewes with single and twin lambs.
Results and Discussion The results showed that the blood glucose, total protein, albumin and calcium on days 90, 120 and 140 of pregnancy were less than 15 days prior to mating but blood urea nitrogen and cholesterol levels were increased. These variations could originate from fetus metabolism since fetus requirements for tissue growth, muscles and bones increases during pregnancy, which should be supplied from maternal body reserves. The comparison of blood metabolites on the both crossbred and purebred pregnant ewes showed that in the late pregnancy, twin pregnant ewes had less glucose, total protein and calcium and more blood urea nitrogen and cholesterol compared with single pregnant ewes because there is a higher fetus requirement for twin fetuses during gestation. Our results also showed that glucose, total protein, albumin and blood urea nitrogen levels of crossbred ewes were higher than purebred Ghezel ewes on 15 days prior to mating period. This may be due to different genetic potential of these breeds. During the gestation period, levels of mentioned metabolites except for blood urea nitrogen were higher in both single and twin crossbred pregnant ewes than purebred Ghezel ewes significantly. It is seemed that these differences may be related to variation in the genetic potential of studying animals.
Conclusion The results of present study showed that there were no signs of pregnancy toxemia in the two experimental groups; however some differences among blood metabolites of purebred and hybrid ewes were found, which may originate from genetic potential of these two groups. These differences revealed that hybrid ewes are more resistant against blood metabolite changes during late pregnancy. Study of fluctuations in the blood metabolites during several stages of pregnancy can help us to determine abnormal metabolic cases and prediction of metabolic disorders such as pregnancy toxemia or ketosis, fatty liver syndrome and disease relating to fetus and ewe metabolism.