EFFECT OF MILD HYPERTHYROIDISM ON SEASONAL AND YEARLY EGG PRODUCTION OF FOWLS WITH ADVANCING AGE

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Abstract
A group of White Leghorn hens in their 5th laying yr., fed 10 gs. of thyropro-tein/100 lbs. complete feed, were observed to lay an av. of 93.8 eggs each during the year. Similar control hens laid an av. of 58.9 eggs each. The hens fed thyroprotein maintained egg production at a higher level during the spring and summer than the control hens. This suggests that the seasonal decline in egg production is due to reduced thyroid secretion with higher environmental temp. During a 3 yr. period in which thyroprotein has been fed continuously, those birds stimulated to a mild hyperthyroid state produced 11.2% more eggs during the 3d yr., 25.7% more during the 4th yr. and 52.5% more eggs during the 5th yr. It is concluded that a mild degree of hyperthyroidism continuously induced in fowls with advancing age tends to inhibit the rate of senescence (as measured by egg production) without affecting the mortality rate.