Effects of UVB exposure (UVB) and dietary vitamin D3 (D3) on egg weight (A), egg shell thickness (B), and egg shell stability (C) over 4 weeks. Data in the panels represented means (n = 9). Data were analyzed by two-way ANOVA with the classification factors UVB exposure, vitamin D3 in the diet, and the interaction between both factors. (A) No significant difference. (B) Effect of vitamin D3 (week 2): p<0.05, UVB × vitamin D3 (week 2): p<0.05. Effect of vitamin D3 (week 3 and 4): p<0.01, UVB × vitamin D3 (week 3 and 4): p<0.10. (C) Effect of UVB (week 2): p<0.05. Effect of UVB (week 3): p<0.10, vitamin D3 (week 3): p<0.10. Effect of UVB (week 4): p<0.01, vitamin D3 (week 4): p<0.05, UVB × vitamin D3 (week 4): p<0.05. Data were additionally analyzed by paired t-test, *significantly different from baseline.