1475 Bioavailability of different sources of zinc using stable isotopes in male Holstein calves

Abstract

Trace minerals are an important component of ruminant nutrition. Furthermore, understanding the bioavailability of various trace mineral sources is essential for accurate dietary formulation. The objective of this trial was to determine bioavailability of Zn when provided in either an inorganic or an organic form. Sixteen weaned male Holstein calves (BW = 60 ± 2 kg [mean ± SE]) were used in a randomized compete block design. Calves were individually fed a common texturized starter formulated to meet NRC nutrient requirements. Calves were orally administered 4 or 8 mg of Zn from 2 sources: 67Zn oxide and 70Zn-methionine hydroxy analog chelate (70Zn-MHAC). Blood was collected via catheters before isotope administration and 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 36, 48, and 72 h after isotope administration for determination of isotope enrichment. Calves were euthanized 72 h after isotope administration, and target tissues were weighed and sampled for determination of isotope enrichment. Plasma area under the curve (AUC) for isotope enrichment was significantly (P < 0.01) greater with 70Zn-MHAC (2.02 ± 0.12 ppm) compared with 67Zn oxide (1.20 ± 0.12 ppm). When dose was considered, plasma AUC for isotope enrichment was significantly (P < 0.01) greater with 8 mg of labeled Zn (2.34 ± 0.12 ppm) compared with 4 mg (0.87 ± 0.12 ppm). Isotope enrichment was significantly (P < 0.01) greater with 70Zn-MHAC compared with 67Zn oxide for all tissues with the exception of omasal tissue, which tended (P = 0.07) to be greater. When dose was considered, isotope enrichment was significantly (P < 0.01) greater with 8 mg of labeled Zn compared with 4 mg for all tissues except muscle (P = 0.17) and tibia (P = 0.42). The slope for 70Zn-MHAC was significantly (P ≤ 0.01) higher compared with that of 67Zn oxide for abomasal tissue (0.036 vs. 0.011; r2 = 0.88), duodenal tissue (0.070 vs. 0.043; r2 = 0.90), ileal tissue (0.069 vs. 0.028; r2 = 0.95), jejunal tissue (0.072 vs. 0.024; r2 = 0.93), liver (0.096 vs. 0.012; r2 = 0.83), muscle (0.016 vs. −0.031; r2 = 0.89), pancreas (0.076 vs. 0.003; r2 = 0.82), thymus (0.023 vs. −0.003; r2 = 0.85), and tibia (0.007 vs. −0.003; r2 = 0.86). Together these data demonstrates using stable isotopes as a valid technique to measure bioavailability and greater bioavailability was observed from Zn-MHAC when compared with zinc oxide.