The behavior of growth-influencing and steroid hormones in the blood plasma during pregnancy of Awassi sheep in Syria

In 11 Awassi ewes of a flock of 30 animals continuous investigations were carried out on the changes of somatogenic (growth hormone-GH, prolactin-PRL, insulin-like growth factor I-IGF-I) and steroid hormones (progesterone--PG, estradiol-17 beta-E2) in blood plasma during a gestation period. Eight animals were pregnant (3 with twins), 3 non-pregnant ewes served as control animals. Pregnancy is associated with an increase in the concentrations of the steroid hormones in blood plasma, they decrease markedly already prepartal (PG) or directly at term (E2), reflecting the placental origin of both hormones. Ewes with twins have higher concentrations of both steroid hormones in their blood plasma than animals with a single fetus. During pregnancy the concentrations of IGF-I in blood plasma increase continuously and normalize rapidly after birth. The relationship between the duration of the pregnancy and the concentration of IGF-I can be described by a quadratic regression, further positive correlations exist between the concentrations of IGF-I and PG or E2 in blood plasma, but a negative correlation between IGF-I and PRL. The concentration of PRL diminishes during the gestation, which reflects increasing seasonal influences (decreasing day length and environmental temperature). The concentration of GH shows a steady level throughout the gestation period. Both hormones increase markedly at term, which represents an attendant circumstance of the birth. From all hormones investigated in blood plasma of the ewes only the concentration of IGF-I exhibits a strong positive correlation with the birth weight of their lambs. This can be taken as a first hint to the ability of IGF-I to promote directly the fetal growth.