The aim of this study was to evaluate the physiological parameters and thermal comfort indices of commercial layers
fed diets containing different levels of vegetable glycerin. A total of 378 Hy-Line White layers at 32 weeks of age were
housed in a shed at nine birds per cage. The experiment lasted 84 days. Treatments consisted of a control diet (without
glycerin) plus five diets with increasing levels of vegetable glycerin (3, 6, 9, 12, and 15%). The black globe humidity
index (BGHI) and radiant heat load (RHL) were out of the thermal comfort zone and were higher in the afternoon period
in all production cycles. Respiratory frequency was lower in the morning, when 3% glycerin were added to the diet. The
surface temperatures of comb, wattle, back, wings, head, and feet did not differ with the glycerin levels and were higher
in the 2nd cycle, but within the range recommended for the species. Glycerin inclusion levels of up to 12% can be used
to partially replace corn in diets for layers housed in sheds covered with ceramic tiles without compromising their
thermoregulation in a hot environment.