Growth performance, metabolic, and hematological markers in Fleckvieh dairy calves fed milk replacer or whole milk

Early life is a critical phase for dairy calves, influencing their growth, metabolism, and overall health. This study aimed to evaluate the effects of feeding either whole milk (WM) or milk replacer (MR) on growth performance, metabolic markers, and hematological parameters from birth until weaning at 60 d of age in Fleckvieh dairy. Eighteen heifer calves were assigned to one of 2 dietary treatments: WM (n = 9; DM basis, 29.1% protein, 27.3% fat, and 37.3% lactose; 5.25 Mcal/kg of DM) or MR (n = 9; DM basis, 22.9% protein, 19.1% fat, and 51.73% lactose; 4.76 Mcal/kg DM; Elvor, Maen Roch, France). The MR was prepared at 130 g/L to match solids content in WM. Calves were housed in individual hutches, fed 3 L of milk twice daily until 53 d and then 3 L of milk once daily until weaning (60 d). Calves had ad libitum access to starter and intake was recorded daily. Growth performance was assessed through BW and period-specific ADG (gain per day between successive weighings), whereas metabolic and hematological markers were analyzed through plasma biomarkers and blood cell counts, respectively. Data were subjected to ANOVA using the GLM procedure for single measures and the GLIMMIX procedure for repeated measures. Despite similar total DMI, calves fed WM exhibited an overall greater BW and greater period-specific ADG (0.77 vs. 0.85 kg/d in MR and WM, respectively), and from 21 to 60 d, WM calves were 3.8 kg heavier than MR-fed calves. From the metabolism standpoint, feeding WM resulted in overall greater plasma concentrations of glucose, urea, cholesterol, alkaline phosphatase, and Ca, but lower bilirubin. Specifically, WM calves had greater paraoxonase activity at 35, 45, and 60 d (weaning), greater ceruloplasmin levels at 15, 21, and 28 d, and greater Mg at 60 d of age. Among hematological parameters, WM calves had greater circulating total leukocytes at 21 and 28 d of age due to enhanced neutrophils. Although WM calves consumed milk with greater proportions of fat and protein and lower lactose content, the intake of milk and starter DM and total energy was similar compared with MR calves. However, considering the better growth rate of WM calves (especially in the second week of life), the better balance between fat, protein, and lactose suggests that feeding WM can enhance bioavailability of nutrients. Further research is needed to explore the long-term implications of these feeding strategies on calf health and productivity, particularly in relation to sustainability and economic feasibility.