Effects of zinc supplementation forms (ZnO, Zn-Lysine, Nano-ZnO) on growth performance and metabolic health in pre-weaned Holstein calves

The pre-weaning period is critical because early-life nutrition and management influence growth, metabolic function and Rumen development, thereby affecting subsequent productivity in dairy calves. Zinc (Zn) supplementation plays a key role in supporting these processes through its involvement in enzymatic activity, antioxidant defense systems, and metabolic regulation, but conventional sources often have bioavailability limitations due to the formation of insoluble complexes in the gastrointestinal tract. This study addresses this challenge by evaluating three Zn forms (ZnO, Zn-lysine, and nano-ZnO) to identify the most effective source for enhancing growth rates, nutrient utilization, and metabolic health. Twenty-four newborn Holstein calves, each with an initial body weight of 40.5 ± 4.24 kg, were selected and randomly allocated to receive one of three treatments: ZnO, Zn-lysine, and nano-ZnO supplementation. Each calf received 80 mg of Zn daily. Supplementation with nano-ZnO increased dry matter intake (P < 0.01), average daily gain (P < 0.01), and hip width (P < 0.01) compared to Zn-lysine and ZnO. However, there were no differences in feed conversion ratio. The treatments did not affect apparent digestibility or rumen fermentation, except for a lower rumen ammonia nitrogen concentration in the nano-ZnO group compared to the other two treatments (P < 0.01). Regarding blood parameters, calves receiving Nano-ZnO showed higher blood triglyceride concentration (P = 0.04) and superoxide dismutase activity (P < 0.01), while blood D-lactate concentration was lower in the nano-ZnO and Zn-lysine groups than in the ZnO group (P = 0.01). Additionally, both fecal consistency (P = 0.02) and nasal discharge (P < 0.01) scores were significantly reduced in the nano-ZnO group. In summary, the study suggests that nano-ZnO is a more effective Zn source and an efficient additive for improving dairy calf performance.