Plasma estradiol, thyroid hormones, and liver lipid content in laying hens fed different isocaloric diets

Two experiments were conducted with laying hens fed a corn-soy basal diet or diets containing fish meal, distillers dried grains with solubles (DDGS) or torula yeast formulated to be isocaloric and isonitrogenous with the basal diet. One half of the hens were kept at a temperature range of 13-24 degrees and the other half at 24-35 degrees for 49 days in experiment 2. Liver lipid content was significantly lower in hens fed DDGS (experiment 1) and DDGS or fish meal (experiment 2) than in hens fed the corn-soy basal diet, but it was not influenced by environmental temperature. Feeding DDGS or fish meal reduced lipoprotein lipase activity in adipose tissue. High temperature reduced plasma estradiol level but not thyroid hormone levels. Plasma estradiol in the hens fed DDGS or fish meal (experiment 1) and DDGS, fish meal or torula yeast (experiment 2) an plasma thyroxine and triiodothyronine in hens fed the DDGS or fish meal at 24-35 degrees in experiment 2 were significantly lower than that of hens fed the corn-soy basal diet. Significant correlations were observed between liver lipid content and plasma estradiol or thyroxine concentrations. These findings show that plasma estrogen and thyroxine levels were influenced by diet composition and that these hormones have a close relation to induction of fatty livers in laying hens.