influences of seasonal variations on thyroid activity and some biochemical parameters of cattle

ABSTRACT

Blood samples were taken from eighteen non-pregnant Holstein heifers to investigate the effects of heat stress on some serum biochemical parameters with emphasis on thyroid hormones. The entire period of study was classified into two seasons, from July to September with mean temperature of 35.5°C [Max 51°C and Min 19°C] and from January to March with mean environmental temperature of 14.5°C [Max 30°C and Min 2°C]. In each season 4 samples were collected every 3 weeks intervals. A significant difference in the concentrations of serum total protein, albumin, glucose, cholesterol BUN, Calcium, T3 and T4 and activities of AST and CK was seen between hot and cold seasons [P<0.05], whereas the concentration of serum inorganic phosphorus was not significant difference between these two seasons. The concentrations of BUN, total protein, albumin and activities of AST and CK in summer were higher than winter, in contrast, the concentrations of glucose, cholesterol, calcium, T3 and T4 were lower in summer than winter [P<0.05]. A significant correlation between T3 and serum glucose, cholesterol, AST and CK was noticed. Mean environmental temperature had a significant correlation with serum T3 glucose, cholesterol, total protein, albumin, BUN, AST and CK. The results of this study showed that very hot conditions had a profound effect on thyroid activity and some serum biochemical parameters