Table 5.

Influence of dietary Zn and ractopamine inclusion on daily micro mineral fecal and urine excretion, and mineral retention of steers as a percent of intake during 5-d collection period

	ZNTRT1			BA1
Item	CON2	SUPZN2	P value4	NON3	RAC3	P value4	SEM
Steers (n)	16	15		15	16
Fecal excretion
Cu, %	78.2	78.9	0.89	76.7	80.5	0.49	3.67
Fe, %	62.0	60.8	0.61	60.6	62.2	0.53	1.71
Mn, %	76.7	69.4	0.06	71.9	74.2	0.50	2.32
Zn, %	64.9	65.7	0.83	63.1	67.4	0.25	2.45
Urinary excretion
Cu, %	0.14	0.11	0.25	0.13	0.12	0.81	0.017
Fe, %	0.12	0.12	0.89	0.12	0.12	0.81	0.018
Mn, %	0.16	0.12	0.37	0.15	0.13	0.50	0.027
Zn, %	0.35	0.13	<0.01	0.26	0.22	0.41	0.035
Apparent absorption
Cu, %	21.8	21.1	0.89	23.3	19.5	0.49	3.67
Fe, %	38.0	39.3	0.51	39.4	37.8	0.53	1.71
Mn, %	23.3	30.6	0.06	28.1	25.8	0.50	2.32
Zn, %	35.1	34.3	0.83	36.9	32.6	0.25	2.45
Mineral retention
Cu, %	21.6	21.0	0.90	23.2	19.4	0.49	3.68
Fe, %	37.9	39.1	0.61	39.3	37.7	0.53	1.72
Mn, %	23.2	30.5	0.05	28.0	25.7	0.50	2.32
Zn, %	34.8	34.2	0.88	36.6	32.3	0.25	2.46

¹ZNTRT (mineral supplementation strategy); BA (β-adrenergic agonist supplementation strategy).

²CON (no supplemental Zn; analyzed 32 mg Zn/kg DM); SUPZN [CON + 60 ppm ZnSO₄ + 60 ppm zinc-amino acid complex (Availa-Zn; Zinpro, Eden Prairie, MN), analyzed 145 mg Zn/kg DM].

³NON (no supplemental ractopamine HCl); RAC (300 mg steer⁻¹ d⁻¹ ractopamine HCl; Actogain 45, Zoetis, Parsippany, NJ).

⁴ZNTRT × BA interaction was not significant (P ≥ 0.19).