Table 6.

Percentages of yolk, albumen, and eggshell of the eggs produced by laying hens fed rations containing different concentrations of caffeine for 12 weeks.

Caffeine in diet	Experimental period
	4 weeks	8 weeks	12 weeks
Percentage of yolk
0 (control)	28.1 ± 0.42	27.9 ± 0.41	27.4 ± 0.27a
150 ppm	28.0 ± 0.40	28.6 ± 0.35	27.6 ± 0.41a, b
300 ppm	28.4 ± 0.37	28.9 ± 0.45	28.4 ± 0.57b
450 ppm	28.2 ± 0.40	28.3 ± 0.30	28.9 ± 0.49b
p	n.s.	n.s.	<0.05
Percentage of albumen
0 (control)	62.3 ± 0.45	62.5 ± 0.47	62.7 ± 0.32
150 ppm	62.6 ± 0.43	62.3 ± 0.44	63.7 ± 0.38
300 ppm	62.6 ± 0.40	62.1 ± 0.44	63.0 ± 0.63
450 ppm	62.9 ± 0.42	63.0 ± 0.34	62.4 ± 0.50
p	n.s.	n.s.	n.s.
Percentage of eggshell
0 (control)	9.61 ± 0.14a	9.64 ± 0.11a	9.87 ± 0.14a
150 ppm	9.42 ± 0.11a	9.16 ± 0.14a, b	8.72 ± 0.18b
300 ppm	9.04 ± 0.12b	8.95 ± 0.10b	8.56 ± 0.20b
450 ppm	8.93 ± 0.14b	8.73 ± 0.15b	8.78 ± 0.17b
p	<0.001	<0.001	<0.0001

Data are shown as mean ± SEM.

^{a, b}Different letters in the same column show significant difference (p < 0.05, Kruskal-Wallis test followed by Student-Newman-Keuls test).

n.s., non-significant.

n = 24.