Table 4.

Least Squares Means (± Standard Error) of the aromatic amino acids, kynurenine, and nitrite in birds at 14 weeks of age according to their feather pecking phenotype (feather pecker: bird that displayed gentle or severe feather pecking at least once between 10–13 weeks of age).

	Gentle feather pecker (n = 103)	Non-gentle feather pecker (n = 251)	P-value
Tryptophan (TRP) (µmol/L)	99 ± 1.2	98 ± 1.0	0.822
Tyrosine (TYR) (µmol/L)	150 ± 2.5	161 ± 1.6	< 0.001
Phenylalanine (PHE) (µmol/L)	97.7 ± 0.94	98.9 ± 0.62	0.314
TRP:(PHE + TYR)	0.40 ± 0.006	0.38 ± 0.005	0.002
KYN:TRP (µmol/mmol)	3.58 ± 0.108	3.42 ± 0.095	0.549
PHE:TYR (µmol/µmol)	0.664 ± 0.0094	0.627 ± 0.0061	0.001
Kynurenine (KYN) (µmol/L)	0.35 ± 0.009	0.36 ± 0.006	0.441
Nitrite (µmol/L)	61 ± 2.3	61 ± 1.5	0.899

	Severe feather pecker (n = 56)	Non-severe feather pecker (n = 298)	P-value
Tryptophan (TRP) (µmol/L)	96.9 ± 1.45	98.8 ± 0.91	0.053
Tyrosine (TYR) (µmol/L)	155 ± 3.5	158 ± 1.5	0.407
Phenylalanine (PHE) (µmol/L)	98.5 ± 1.29	98.5 ± 0.56	0.950
TRP:(PHE + TYR)	0.38 ± 0.007	0.390 ± 0.003	0.367
KYN:TRP (µmol/mmol)	3.7 ± 0.14	3.59 ± 0.086	0.260
PHE:TYR (µmol/µmol)	0.649 ± 0.0130	0.636 ± 0.0057	0.356
Kynurenine (KYN) (µmol/L)	0.35 ± 0.013	0.35 ± 0.006	0.918
Nitrite (µmol/L)	61 ± 3.2	61 ± 1.4	0.966