Table 1.

Performance of broiler chickens supplemented with organic acids as an alternative to antibiotics, submitted or not to microbiological challenge.

		Performance2
		ADG, g		ADFI, g		FCR		VB, %		PF
Effects1		n	LS-Means	n	LS-Means	n	LS-Means	n	LS-Means	n	LS-Means
Additive	CON	371	44.7 b3	365	85.0	367	1.85	57	91.9	54	260.1
	OA	688	45.7 b	670	84.6	673	1.78	119	93.4	113	277.8
	ATB	89	48.5 a	89	84.3	90	1.70	21	93.9	20	314.0
Challenge	–	1063	47.0	1055	84.1	1056	1.73	173	97.5	172	287.3
	+	85	45.6	69	85.1	74	1.82	24	88.7	15	280.6
Additive × Challenge	CON −	345	46.0	343	83.8	344	1.76 b A	50	97.3 a A	49	269.0
	CON +	26	43.4	22	86.2	23	1.94 c B	7	86.6 b B	5	251.2
	OA −	640	47.1	634	83.5	634	1.72 a A	106	97.7 a A	106	293.9
	OA +	48	44.3	36	85.7	39	1.83 b B	13	89.1 ab B	7	261.6
	ATB −	78	48.0	78	85.0	78	1.72 a A	17	97.6 a A	17	299.1
	ATB +	11	49.0	11	83.6	12	1.68 a A	4	90.4 a B	3	328.9
SE		0.58		1.21		0.011		0.36		6.47
Model4	Probability of fixed effects
Additive		0.007		0.918		<0.001		0.001		0.170
Challenge		0.397		0.714		0.021		<0.001		0.866
Additive × Challenge		0.241		0.614		<0.001		0.014		0.539
Age		<0.001		<0.001		<0.001		<0.001		<0.001
Age × Age		<0.001		<0.001		-		<0.001		<0.001

¹CON, control (without additive); OA, organic acids; ATB, antibiotics; −, without challenge; +, with challenge.

²FCR, feed conversion ratio; VB, viability; PF, production factor = (((ADG × VB)/FCR)/10).

³LS-Means (least square means) followed by distinct letters differ by the Tukey-Kramer's test (P < 0.05). In the interactions, lower case letters represent the comparison between the additives (within the absence or the presence of challenge), and upper case letters represent the comparison between the absence and the presence of challenge (within each additive).

⁴Studies (experiments) entered in the model as a random-effect class variable, and the variables age (average between the initial and final age of each evaluation, expressed in d) and age × age entered in the model as fixed-effect covariates.