Season influence on 3,5,3’ triidothyronine (T3), tyroxine (T4) and testosterone (Tes) serum concentration

Abstract

The serum concentration of 3,5,3’triiodothyronine (T3), tyroxine (T4) and testosterone (Tes) was studied, from March 1996 to March 1997, in 24 three-year-old rams. Three breeds were used: Bergamacia breed, nine animals (Be), eighth Corriedale (Co) and seven Hampshire Down (Hd). The blood was collected each 30 days, as well as the meteorolgical data: wind speed (v), air temperature (Ta), globe temperature (Tg) and relative humidity (Ur). Corriedale animals presented increasing values of T3 from March (0.27ng.ml^-1) to December (0.99ng.ml^-1), decreasing in January (0.11ng.ml^-1), and returning to the March values (0.27ng.ml^-1. There was no seasonal effect (P > 0.05) on T3 concentration for the breeds Be (0.17ng.ml^-1) and Hd (0.57ng.ml^-1). As for T4, the Corriedade had lower values from March (7.67ng.ml^-1) to August (3.92ng.ml^-1), with higher ones in January (12.33ng.ml^-1). Hampshire animals presented increased T4 concentration from March (3.54ng.ml^-1) to October (5.61ng.ml^-1), decreasing until January (2.16ng.ml^-1) (summer). For the Bergamacia there was a decrease of T4 in March (4.73ng.ml^-1) and after, with the lowest value in December (3.77ng.ml^-1), and going up again in January (4.95ng.ml^-1). Serum concentration of Tes was significant (P < 0,01) for Hd, being higher from March (2.38ng.ml^-1) to December (6.75ng.ml^-1), decreasing in January (1.41ng.ml^-1), increasing again, and reaching March prior values (2.38ng.ml^-1). There was no seasonal effect (P > 0,05) on the Tes for Be (4.15ng.ml^-1) and Co (3.21ng.ml^-1).