Effect of dietary supplementation with different levels of fennel seed (FS) on the slaughter traits of broilers. Treatment groups: C, FS10, FS20, and FS30 indicate the supplementation of fennel seed at the rate of 0, 10, 20, and 30 g/kg of diet, respectively. Variables of slaughter traits are determined as a percentage of the live body weight. Bars express the means ± standard error of means (n = 20 birds per treatment group). P-value of the linear (L) and quadratic (Q) effects of FS levels are indicated for each variable.