Tucker Stable Isotope Dose Plasma Response Figure

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 the suitability of stable isotopes as a marker of bioavailability and the bioavailability of Zn when provided in either an inorganic or organic form to ruminating Holstein calves. Eighteen weaned male Holstein calves were utilized in a randomized complete block design. Calves were fed a basal diet formulated to meet nutrient requirements, offered as a texturized starter on an individual basis. Calves were orally administered 0, 4, or 8 mg of Zn from 2 sources: ⁶⁷Zn sulfate (Zn-SO) and ⁷⁰Zn-methionine hydroxy analogue chelate (Zn-MHAC) as a pulse dose. Blood was collected via catheters prior to isotope administration and 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 8, 10, 12, 24, 30, 36, 48, 54, 60, and 72 h after isotope administration for determination of isotope enrichment. Calves were humanely euthanized 72 h after isotope administration and target tissues harvested, weighed, and sampled for determining isotope enrichment. No differences were observed in weight of target organs due to isotope dose, except for liver which was elevated with 4 mg compared to 0 and 8 mg. With area under the curve for plasma Zn enrichment, effect of source was not significant nor was there a significant interaction between source and isotope dose. The effect of isotope dose was significant resulting in 8 mg being greater than 4 mg and 4 mg being greater than 0 mg for plasma Zn enrichment area under the curve. When enrichment of tissues was determined for all tissues harvested, Zn-MHAC resulted in significantly greater enrichment than Zn-SO for abomasum, duodenum, hoof, ileum, lung, omasum, reticulum, skin, spleen and metatarsal bone, while heart tissue and microbial pellet tended to have greater enrichment for Zn-MHAC than Zn-SO. When 8 mg of Zn were provided, it resulted in significantly greater enrichment than 4 mg of Zn in all harvested tissues. Overall, this suggests that Zn-MHAC is absorbed to a greater extent than Zn-SO due to its ability to enrich the majority of sampled tissues at a greater level.