Table 4.

Effects of heat stress and dietary betaine on digestive enzyme activity of yellow-feathered broilers*, U/mg protein.

Dietary Betaine Levels (mg/kg)	Temperature	Duodenum		Jejunum		Ileum
		Trypsin	Lipase	Trypsin	Lipase	Trypsin	Lipase
After 5 Weeks Heat Stress
0	TN	248	1.76	351	1.69	346	1.71
0	HS	179	1.30	247	1.33	315	1.63
500	HS	172	1.72	361	2.68	380	2.25
1000	HS	196	1.05	310	1.36	335	1.65
2000	HS	189	1.36	271	1.40	333	1.55
SEM		33.1	0.518	32.6	0.491	54.0	0.462
Contrast		p-value
TN vs. HS		0.151	0.537	0.035	0.605	0.686	0.904
Linear		0.590	0.845	0.898	0.653	0.975	0.695
Quadratic		1.000	0.926	0.038	0.239	0.559	0.461
After 10 Weeks Heat Stress
0	TN	225	0.89	414	1.61	293	0.64
0	HS	116	0.55	313	0.91	243	0.60
500	HS	183	1.23	264	1.31	216	0.50
1000	HS	201	0.43	418	2.35	293	0.54
2000	HS	250	0.99	258	1.85	263	0.81
SEM		40.4	0.382	56.7	0.703	41.3	0.178
Contrast		p-value
TN vs. HS		0.105	0.528	0.296	0.488	0.406	0.865
Linear		0.044	0.767	0.972	0.249	0.480	0.287
Quadratic		0.849	0.879	0.327	0.539	0.978	0.339

* TN, thermoneutral zone; HS, heat stress; SEM, standard error of means; TN vs. HS, TN group vs. HS control (0 mg/kg betaine) group.