The article assumes that any biosystem is characterized by a certain ordered interconnection between its elements. It turns the organism into a purposefully functioning system. In this regard, structural and functional unity as a general rule of the biosystem existence concerning blood gets a special significance: blood content as an integrative indicator is related to the state of the organism as a whole, to the intensity of metabolism, and to breeding and productive qualities. It is revealed not only at the level of quantitative changes in its parameters, but also at the level of the correlation relationship. The content of thyroid stimulating hormone of the pituitary gland (TSH)) in the blood of laying hens didn’t not reliably depend on the duration of the reproductive period and varied in the range of 0.40 ± 0.003 - 0.41 ± 0.009 μIU/ml. The level of triiodothyronine (T3) fluctuated practically at the same level, amounting to 3.00 ± 0.11 - 3.25 ± 0.16 pg/ml, although it had a tendency to decrease during the oviparity. The concentration of thyroxine (T4) depended more significantly on the age of laying hens. The minimum level of the hormone was contained in the blood of 26-week-old laying hens (7.45 ± 0.85 pmol/l), increasing by the 52nd week in 1.22 times; it amounts to 9.10 ± 0.26 pmol/l. At the end of oviparity (80 weeks of age), the T4 amount was 8.75 ± 0.55 pmol/l. Blood albumin directly influenced the thyroid profile of the organism in laying hens. This was due to the fact that more than 99% of thyroid hormones circulating in the blood are associated with plasma proteins, including the albumin fraction. The number of significant correlations was greatest at 26 and 52 weeks of age of laying hens, corresponding to periods of maximum egg production, i.e., egg production of laying hens is the result of the relationship between the thyroid profile of the bird’s organism and the intensity of metabolic processes. Triiodothyronine, regulating the catalytic activity of AST, maintains the appropriate intensity of catabolic processes, energy synthesis and distribution.