Changes in Thyroid Hormones Serum Profiles During Late Pregnancy and Post Lambing in the Awassi Sheep

Abstract

Thyroid gland (TG) function and thyroid hormones (TH) activities are vital to sustaining the productive performance of sheep. Changes in serum TH concentrations are an indirect measure of the changes in thyroid activity and circulating TH, which are considered indicators of the metabolic and nutritional status of the animals. Pregnant Awassi ewes (n=17) were utilized to assess the changes in the serum profiles of thyroid-stimulating hormone (TSH), 3,3',5-triiodothyronine (T3), and thyroxine (T4) 4 days prior to lambing (D/BL) and at 2,6,10,14,18 and 22 weeks post-lambing (W/PL). Our study revealed the TSH serum profile had gradually and significantly increased (p< 0.05) between 4D/BL and 22W/PL. TSH levels recorded their lowest drop at 4D/BL, while also peaking at 22W/PL. TSH levels at 22W/PL was two times as high as the TSH levels at 4D/BL. Here we demonstrated that T3 concentration didn't exhibit a particular trend throughout all intervals and that the T3 levels attained their peak levels at 2W/PL, while these levels dropped significantly at 14W/PL. Furthermore, we exhibited a significant decrease in T4 level (p < 0.01) at 6W/PL, while a significant increase (p<0.05) in its level was recorded at l0W/ PL. T4 levels did not display any specific pattern; apart from its lowest concentration at 6W/PL and its highest at 10W/PL, the T4 levels remained almost in parallel, with minor fluctuations throughout all intervals. Analysis of the T4:T3 ratio at various intervals didn't reveal any specific trend. Our study provides vital elements on the serum profiles of TH in pre-and postpartum periods, which mirrors physiological changes and allows the monitoring and manipulation of thyroid physiology, to improve animal health and production.