Influence of dietary zinc concentration and supplemental zinc source on nutrient digestibility, zinc absorption, and retention in sheep

The objective of this study was to assess whether supplemental Zn source or concentration would affect ruminant Zn retention and nutrient digestibility. Thirty-six weaned crossbred Polypay wethers, were sorted by BW to 3 periods and stagger started on a common diet (22 mg Zn/kg DM) for a 52-d depletion period. Day 52 BW was used to assign Zn treatments (3 lambs/treatment/period): no supplemental Zn (CON), or supplemental Zn (40 mg Zn/d) from Zn sulfate (ING; Zinc Nacional, Monterrey, SA, Mexico), Zn methionine (ORG; Zinpro 120; Zinpro, Eden Prairie, MN), or Zn hydroxychloride (HYD; IntelliBond Z; Micronutrients USA LLC, Indianapolis, IN). On day 53 (day 1 of Zn treatments), lambs were moved to metabolism crates for 10 d of adaptation and 5 d of total fecal and urine collection. Blood for plasma Zn analysis was collected on day 52 and day 68. Data were analyzed as a randomized complete design with fixed effects of treatment, period and the interaction, which was significant (P >= 0.19) for day 68 plasma Zn but was removed for all other variables. Contrast statements were used to separate treatment means: CON vs. ZINC (ING, ORG, HYD), ING vs. HYD, and ORG vs. HYD. Day 52 plasma Zn concentrations were similar when CON was compared with ZINC (P = 0.84), and when ING and ORG were compared with HYD (P >= 0.19). Dry matter and neutral detergent fiber digestibility were lesser in ORG compared with HYD (P = 0.05) and organic matter and acid detergent fiber digestibility tended (P <= 0.08) to be lesser in ORG compared with HYD. Intake and fecal excretion of Zn was lesser, while apparent absorption of Zn was greater, in CON compared with ZINC (P <= 0.001). Zinc retained as a percent of Zn intake was greater in CON compared with ZINC (P = 0.001). Zinc retained (mg/d) was similar in CON compared with ZINC (P = 0.58) and when ING or ORG were compared with HYD (P >= 0.83). There was a treatment x period interaction for day 68 plasma Zn where treatments did not differ for periods 1 and 3 but ORG lambs had increased plasma Zn in period 2 compared with other treatments (P = 0.02). Lambs receiving no supplemental Zn had increased apparent absorption, suggesting Zn absorption may be upregulated in these lambs. Similarities in Zn retention across treatments suggests Zn requirements of these lambs were met regardless of supplementation concentration or source. Nutrient digestibility was improved in HYD lambs compared with ORG, and further work is needed to clarify the influence of supplemental Zn source on nutrient digestion.