​Effects of dietary betaine supplementation on (A) the average number of follicles per field at different follicle stages in laying hens exposed to a heat stress challenge; (B) effects of environment on the average number of follicles per field at different follicle stages in laying hens; and (C) representative images for hematoxylin and eosin staining for ovarian follicle counts. Treatments: TNCON = thermoneutral (TN) and a control diet, TNBET = TN and a control diet supplemented with dietary betaine, HSCON = heat stress and a control diet, and HSBET = Heat stress and a control diet supplemented with dietary betaine​