Table 4. Effect of protease dietary supplementation on nutrient digestibility of dry matter, crude protein, energy, calcium, phosphorus, and amino acids in broilers¹⁾

Items (%)	CON	T1	T2	T3	SEM	p-value
Items (%)	CON	T1	T2	T3	SEM	Linear	Quadratic
Dry matter	68.24^b	70.49^ab	70.66^ab	72.58^a	0.18	0.001	0.387
Crude protein	73.42^b	76.13^a	76.32^a	76.67^a	0.21	0.048	0.604
Energy	73.15^b	75.03^b	75.16^ab	76.81^a	0.46	0.003	0.596
Ca	59.8	60.78	61.02	61.5	1.11	0.295	0.825
P	46.05	47.4	47.9	48.39	1.72	0.339	0.802
Amino acids
Lysine	84.83^b	87.72^a	89.31^a	89.87^a	0.89	0.003	0.546
Methionine	87.62^b	90.93^a	92.44^a	93.83^a	0.90	0.001	0.675
Cysteine	73.21^b	3.81^b	4.2^ab	5.92^a	0.58	0.037	0.453
Threonine	1.22^b	3.14^a	4.83^a	85.75^a	0.74	0.006	0.876
Arginine	6.43	6.91	7.32	7.72	0.77	0.234	0.432
Isoleucine	0.34^b	2.53^ab	4.31^ab	6.45^a	1.29	0.001	0.765
Leucine	77.82^b	78.94^ab	80.64^ab	81.54^a	0.82	0.002	0.568
Histidine	84.41^b	86.22^ab	88.75^a	88.81^a	1.05	0.001	0.882
Phenylalanine	82.63	83.31	83.72	83.62	0.24	0.348	0.322
Tyrosine	84.21	84.94	85.42	85.94	0.35	0.128	0.452
Tryptophan	71.83^b	73.42^ab	74.31^ab	74.64^a	0.62	0.036	0.645

Treatment groups: CON, basal diet; T1, basal diet + 0.03% protease; T2, basal diet + 0.06% protease; T3, basal diet + 0.09% protease.
Means in the same row with different superscripts differ (p < 0.05).