Long-term induced hyperthyroidism in breeder hens: Effects on blood plasma biochemical attributes, indicators of oxidative stress, and markers of liver function

Abstract

A 4-week-long administration of extra thyroxine in broiler breeder hens was suggested to reduce the cold-induced ascites in their offspring. In the present study the hypothesis was tested to disclose the plausible adverse effects of long-term maternal hyperthyroidism (100 days) on blood plasma biochemical attributes, indicators of oxidative stress, and markers of liver function in the exposed breeder hens. Also, the association between egg production rate and egg shell strength with alkaline phosphatase activity of plasma were tested. Seventy 47-week-old Cobb 500 breeder hens were randomly allotted to two treatment groups as control (CON) and hyperthyroid (HYPER), each consisting of five replicates of seven birds. Thyroxine (T4; 0.3 mg/bird/d) was orally administered to the HYPER group for 100 consecutive days; whereas the CON group received the drinking water only. Blood sampling was done every 5 week from 47 to 64 week of age for quantification of plasma T4 and T3, and biochemical attributes as well as indicators of oxidative stress. Results indicated that plasma concentration of T4 was greater for the HYPER birds (P 〈 0.05); however, that of T3 was not different between the experimental groups. Total cholesterol, HDL, LDL, and VLDL, and triglyceride concentrations were not affected by T4 administration. Induced hyperthyroidism had no apparent effect on in vitro plasma lipoperoxidation indices, including CDMax, CDAUC, and CD lag phase; whereas, CD oxidation rate and MDA were greater in HYPER group as compared with their CON counterparts. The effect of oral T4 on plasma aspartate aminotransferase and alanine aminotransferase was not significant although the plasma level alkaline phosphatase was higher in HYPER birds (P > 0.05). No significant treatment effect was observed on egg production. Hens belonging to HYPER group recorded a higher egg shell thickness than those of the CON birds, although the correlation coefficient of egg shell thickness with plasma concentration of alkaline phosphatase was not significant. Overall, apart from the changes in parameters evaluated, the values were within their biological ranges. Therefore, it might be stated that the long term administration of T4 did not adversely affect the biochemical characteristics of broiler breeder hens. Future studies are needed to make a final decision on use of this treatment to reduce the ascites incidence in offspring.