Table 5.

The effect of supplemental Zn for 79 d and ractopamine hydrochloride supplementation (300 mg·steer⁻¹d⁻¹) for 31 d on finishing steer plasma and liver mineral and plasma cAMP¹

	Treatments2							Contrast P-values3
Variable	CON	ZnAA0	ZnAA60	ZnAA90	ZnAA120	ZnAA150	SEM	LZn	QZn	CON vs. Zn
Pens	8	8	8	7	8	8
Plasma mineral,4 mg/L
Cu	1.09	1.02	1.02	1.03	1.01	0.95	0.027	0.10	0.14	0.01
Fe	2.08	2.02	1.90	2.19	2.16	1.91	0.062	0.89	0.12	0.55
Zn	1.21	1.27	1.24	1.34	1.36	1.37	0.032	0.007	0.48	0.005
Plasma cAMP5, pmol/L	0.79	0.63	0.54	0.60	0.62	0.57	0.055	0.75	0.66	0.003
Liver mineral, mg/kg DM
Day 456
Cu	346	285	277	296	261	241	26.7	0.26	0.38	0.01
Fe	173	177	185	185	194	160	11.9	0.64	0.12	0.61
Zn	96	113	122	124	115	119	8.5	0.71	0.47	0.02
Day 80 (collected at harvest)7
Cu	419	321	337	359	312	296	27.0	0.50	0.17	0.003
Fe	191	165	164	159	158	155	12.4	0.50	0.87	0.03
Zn	139	140	153	144	154	154	8.5	0.25	0.82	0.28

¹One randomly selected animal was sampled per pen.

²Treatments: a dry-rolled corn-based diet supplemented with 0 mg Zn/kg from ZnSO₄ and no supplemental ZnAA (CON; analyzed 30 mg Zn/kg DM), 60 mg Zn/kg from ZnSO₄ and no supplemental ZnAA (ZnAA0; analyzed 95 mg Zn/kg DM) or ZnAA0 diet supplemented with 60 (ZnAA60; analyzed 152 mg Zn/kg DM), 90 (ZnAA90; analyzed 188 mg Zn/kg DM), 120 (ZnAA120; analyzed 209 mg Zn/kg DM) or 150 (ZnAA150; analyzed 230 mg Zn/kg DM) mg Zn/kg DM from ZnAA.

³Contrasts: LZn = the linear effect of ZnAA; QZn = the quadratic effect of ZnAA. CON vs. Zn = CON vs. ZnAA0, ZnAA60, ZnAA90, ZnAA120, and ZnAA150.

⁴Based on repeated measures from day 0, 48, 62, and 79, treatment × day: P ≥ 0.72.

⁵cAMP = cyclic adenosine monophosphate; Based on repeated measures from day 48, 62, and 79, treatment × day P = 0.78.

⁶Liver samples were collected via biopsy (Engle and Spears, 2000).

⁷Liver samples were collected at abattoir postharvest.