The objective of this study was to evaluate the effects of sodium butyrate and organic zinc supplementation, alone or combined, on performance, zinc metabolism, blood parameters, and gut health in Holstein calves highly challenged by heat and diarrhea during the pre-weaning and weaning periods. Forty-eight male calves were assigned to one of four treatments: control (CON), SB (3 g/kg of sodium butyrate in dry matter [DM]), OZn (262 mg/kg of organic zinc in DM), or SBOZn (3 g/kg of sodium butyrate and 262 mg/kg of organic zinc in DM). Calves were monitored from days 7 to 63 for feed intake, weight gain, body morphometry, fecal score, and blood parameters. Zinc balance was evaluated from days 45 to 49, and 24 calves were slaughtered on day 64 for jejunal sampling to assess tight junction gene expression. Diarrhea incidence was high (>90%) across groups. Fecal scores varied over time but did not differ between treatments. The OZn and SBOZn groups had higher Zn intake, with greater absorption and retention of the mineral compared to the CON and SB groups. Additionally, the OZn group tended to have higher serum Zn concentrations. SB and OZn, separately or combined, had limited effects and did not consistently improve the performance or health of calves highly challenged during pre-weaning and weaning.

This study aimed to evaluate the effects of an ultra-diluted complex on the health status, growth performance, and blood parameters of dairy calves during the preweaning phase in a double-blind, placebo-controlled trial. During a 75-period trial, thirty-four Holstein newborn calves at the second day of life were completely randomized individually into two treatments: (1) control (CON), oral saline supplementation (5 mL/d); and (2) oral supplementation with 5 mL/d of a ultra-diluted complex (UD): Sulfur: ${10}^{60}$ + Viola tricolor: ${10}^{14}$ + Caladium seguinum: ${10}^{30}$ + Zincum oxydatum: ${10}^{30}$ + Phosphorus: ${10}^{60}$ + Cardus marianus: ${10}^{60}$ + Colibacillinum: ${10}^{30}$ + Podophyllum: ${10}^{30}$ + Vehicle: alcohol. Free access to water and a starter was ensured during the trial period. Feed intake and fecal and health scores were monitored daily. Calves were weighed and measured weekly. Blood samples were collected at enrollment on the first day and every 21 days until the 75th day, 2 h after morning milk feeding, and tested for hematology, blood urea nitrogen, aspartate aminotransferase, gamma-glutamyl transferase, total protein albumin, globulin, and creatinine. At 70 days of age, calves were disbudded following the standard management practices of the farm. The inflammatory profile, including Immunoglobulin A, Immunoglobulin G, ceruloplasmin, transferrin, albumin, and haptoglobin, was quantified in serum samples. The ultra-diluted complex was ineffective in reducing the incidence of diseases, starter feed intake, daily weight gain, and body measurements and inflammatory profile. Blood parameters were also not affected. Thus, the ultra-diluted complex was inefficient in reducing the incidence of diseases and did not affect the performance and metabolites of pre-weaned Holstein calves.