Concentrate feed intake, metabolic response and growth in German Holstein bull calves vary depending on the composition of milk replacer and starter feed

Early-life nutrition affects growth, metabolic development, and subsequent productivity of dairy calves. This study aimed to explore whether a calf starter feed composed on basis of a mixture of the native legume pea ( Pisum sativum , 30%) and rapeseed (10%), can support performance-oriented calf rearing of conventionally reared calves, and whether the responses differ between qualities of milk replacers. Therefore, forty-nine male German Holstein calves were randomly assigned to a 2 × 2 factorial design comparing milk replacers based on either skimmed or whole milk and calf starters containing either soybean meal or a mixture of pea and rapeseed extraction meal. Milk replacer and starter intake, growth performance (body weight, average daily gain, back and body length, heart girth, withers and hip height), and selected blood metabolites related to energy and lipid metabolism were recorded. Back fat thickness and rib fat thickness were measured using ultrasonography before and after weaning. Calves fed whole milk-based milk replacer had a better growth performance (body weight ( P time × MR = 0.005) and back length ( P time × MR = 0.029) during the trial and greater average daily gain during the preweaning period ( P time × MR = 0.009). Starter intake increased mainly during weaning ( P time < 0.001), with higher dry matter and energy intake observed in soybean meal-based groups ( P time × CS < 0.001). Differences in further growth parameters were minor and largely temporary. Blood metabolites reflected the metabolic shift during weaning, with glucose concentration decreasing ( P time < 0.001) and β-hydroxybutyrate levels increasing in all groups ( P time < 0.001). Milk replacer formulation influenced lipid metabolism, with higher cholesterol ( P time × MR < 0.001) and cholesterol fraction concentrations ( P time × MR < 0.001) in calves fed skimmed milk-based milk replacer. Under the condition of this study, the pea-rapeseed starter resulted in lower intake than the soybean meal-based starter and did not support starter and milk replacer-derived nutrient intake during weaning. Further work should target palatability by changing the proportion of rapeseed and legume components in the starter mixture of rapeseed-legume-based starters and evaluate longer-term effects on rumen development and performance.