Table 2.

Regression equations, obtained by analysis of variance-covariance, to estimate the performance of broiler chickens supplemented with organic acids as an alternative to antibiotics, submitted or not to the microbiological challenge.

			Intercept			Age			Age × Age
Variables1	Group2		Parameter	SE	P > |t|	Parameter	SE	P > |t|	Parameter	SE	P > |t|
ADG, g	Additive	CON	−5.223	2.84	0.066	3.327	0.167	<0.001	−0.0347	0.0038	<0.001
		OA	−0.821	2.61	0.754	3.257	0.120	<0.001	−0.0341	0.0026	<0.001
		ATB	−0.123	7.68	0.987	3.874	0.604	<0.001	−0.0455	0.0143	0.002
ADFI, g	–	–	−13.39	3.30	<0.001	5.868	0.158	<0.001	−0.0345	0.0035	<0.001
FCR	Additive × Challenge	CON −	1.272	0.030	<0.001	0.0259	0.0010	<0.001	–		–
		CON +	1.170	0.127	<0.001	0.0369	0.0056	<0.001	–		–
		OA −	1.210	0.024	<0.001	0.0266	0.0007	<0.001	–		–
		OA +	1.147	0.074	<0.001	0.0307	0.0031	<0.001	–		–
		ATB −	1.225	0.063	<0.001	0.0255	0.0026	<0.001	–		–
		ATB +	1.292	0.159	<0.001	0.0181	0.0078	<0.062	–		–
VB, %	Additive × Challenge	CON −	100.4	1.52	<0.001	−0.3674	0.127	0.006	0.0086	0.0026	0.002
		CON +	254.4	132.0	0.126	−20.94	17.44	0.296	0.6139	0.5305	0.312
		OA −	99.91	0.85	<0.001	−0.3096	0.062	<0.001	0.0070	0.0013	<0.001
		OA +	90.34	129.0	0.522	0.6579	17.34	0.971	−0.0324	0.5328	0.954
		ATB −	103.3	2.03	<0.001	−0.7014	0.165	0.004	0.0154	0.0035	0.003
		ATB +	118.8	0.63	0.003	−2.648	0.086	0.021	0.0716	0.0028	0.025
PF	–	–	106.5	46.76	0.026	13.52	2.797	<0.001	−0.2415	0.0580	<0.001

¹FCR, feed conversion ratio; VB, viability; PF, production factor = (((ADG × VB)/FCR)/10).

²CON, control (without additive); OA, organic acids; ATB, antibiotics; −, without challenge; +, with challenge.