Table 3.

Effects of ractopamine withdrawal on carcass characteristics

Item	Treatments1							Contrast2P-value
	CON	12-h RAC	2-d RAC	4-d RAC	7-d RAC	SEM3	P-value	L	Q	CON vs. RAC
No. of pens	12	12	12	12	12	—	—	—	—	—
HCW4, kg	411y	415x	416x	417x	415x	1.99	0.006	0.975	0.077	<0.001
Dressing percentage	63.94y	64.25xy	64.28xy	64.58x	64.30xy	0.209	0.069	0.650	0.210	0.017
HCW ADG5, kg/d	1.38y	1.44x	1.46x	1.48x	1.44x	.031	0.006	0.984	0.078	<0.001
Camera grading and measurements
Choice or greater, %	75.9	73.9	71.8	73.6	71.1	3.77	0.500	0.461	0.873	0.173
Sub-select, %	0.41	0.36	0.26	0.18	0.55	0.36	0.842	0.932	0.582	0.927
Marbling score6	453	447	448	454	444	7.5	0.621	0.721	0.219	0.450
YG 1 and 2, %	24.7xy	36.3z	22.8x	31.3yz	33.4yz	4.90	<0.001	0.551	0.005	0.016
YG 4 and 5, %	21.2z	14.6xy	20.5yz	18.2yz	10.9x	3.51	<0.001	0.017	<0.001	0.007
LM7 area, cm2	33.8x	35.1y	34.3x	34.8y	35.3y	0.56	0.002	0.142	0.209	<0.001
Fat thickness, cm	1.40	1.37	1.47	1.40	1.40	0.04	0.312	1.000	0.220	0.879

¹CON = control treatment, fed no ractopamine hydrochloride (RAC; Actogain 45, 100g/kg; Zoetis Inc., Parsippany, NJ); 12-h = fed RAC for 33 d with 12-h withdrawal period; 2-d = fed RAC for 33 d with 2-d withdrawal period; 4-d = fed RAC for 33 d with 4-d withdrawal period; 7-d = fed RAC for 33 d with a 7-d withdrawal period. Cattle on RAC treatments received RAC supplementation corresponding to withdrawal period i.e., 12-h started RAC on day 29 of the feeding period; 2-d started RAC on day 27; 4-d started RAC on day 25; 7-d started on day 22.

²Observed significance levels for orthogonal contrasts: L and Q = linear and quadratic; CON vs. RAC = contrast of control treatment vs. the average of the 12-h, 2-d, 4-d, and 7-d treatments.

³SE of the least square means.

⁴Initial BW used as a covariate in the model.

⁵On the basis of initial HCW (kg), which was calculated as 0.2598·(initial BW^1.1378; Tatum et al., 2012).

⁶As determined by camera; 400 = Small⁰⁰.

⁷Longissimus muscle.

^abcTreatments with unlike superscripts differ (P ≤ 0.10).