Apparent absorption, zinc retention and nutrient digestibility in lambs during an adrenocorticotropic hormone challenge

This study sought to determine if Zn supplementation would increase Zn retention and nutrient digestibility in lambs exposed to adrenocorticotropic hormone. Twenty-two crossbred poly-pay wethers (n = 5-6/ treatment) enrolled in a previous trial had been stagger started on a common diet (22 mg Zn/kg DM) for 52-d, and were placed in metabolism crates for 15-d of dietary treatments: CON: common diet + no supplemental Zn; ZINC: CON + 40 mg/d ZnSO4 top dressed daily in fine ground corn. On d16 lambs were assigned within diet to injected challenge treatments: Saline: 2 mL saline; ACTH: 80 IU adrenocorticotropic hormone. On d17 lambs were placed in crates to facilitate fecal and urine collection, and received injections at 0700h for d17-20. Plasma cortisol was assessed on d16 3h post-feeding, and 3h after injections 1 (d17) and 4 (d20). Data were analyzed as a 2 x 2 factorial; no interactions were found (P > 0.09). Plasma cortisol was greater in ACTH post-injection 1 and 4 (P < 0.002). Zinc intake was greater in ZINC (P < 0.001). Zinc apparent absorption was greater in CON (16.0) vs. ZINC (7.04%; P = 0.002) and tended (P = 0.12) to be lesser in ACTH (9.57%) vs. Saline (13.5%). Day-20 plasma Zn was lesser in CON (0.67) vs. ZINC (0.78 mg/L; P = 0.03). Digestibility was greater in CON vs. ZINC for NDF (45.8% vs. 41.8%) and ADF (33.3% vs. 26.7%; P < 0.03). Dry matter and OM digestibility tended (P < 0.09) to be greater in CON compared to ZINC. Retained Zn was unaffected (P > 0.24) by diet (CON: 4.09 mg/d; ZINC: 4.29 mg/d) or injection (Saline: 4.79 mg/d; ACTH: 3.59 mg/d) suggesting that Zn requirements in lambs may not increase in response to ACTH. Nutrient digestibility may also be affected by supplementation with ZnSO4.