Table 5.

Haugh units 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
0 (control)	91.8 ± 0.74c	87.9 ± 1.10	86.8 ± 1.02b
150 ppm	92.9 ± 0.78b, c	87.5 ± 1.05	92.9 ± 0.83a
300 ppm	94.6 ± 1.25a, b	90.1 ± 1.10	91.5 ± 0.93a
450 ppm	95.7 ± 0.89a	90.2 ± 1.03	94.5 ± 1.08a
p	0.01	n.s.	<0.001

Data are shown as mean ± SEM.

^{a, b, c}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.