Previous studies showed that hcavy milk-fed caIves often develop problems with glucose homeostasis and do not utilise dietary carbohydrates for body fat deposition. This suggests that calves may lack the metabolic capacity for synthesizing fatty acids from glucose. Poor glucose utilisation for growth may aIso be explained by the large supply of dietary fatty acids, allowing synthesis of body fat exclusivcly from dietary fatty acids. The main objective of the current study was therefore to assess encrgy balance, body fat deposition and de nova fatty acid synthesis when exchanging fat for lactose in milk replacer for veal caIves. Sixteen 1-lolstein-Friesian caIves ( 121 ±3 kg) were assigned to either a high-fat (HF: 30% fat) or a low-fat (LF; 10% fat) milk replacer for 12 weeks. This large, iso-encrgetic exchange betwcen fat and lactose did not affect growth performance, protein and energy retention. The respiratory quotient exceeded unit y during several hours per day in LF caIves, but not in HF caIves. The difference in isotope recovery in expired CO2 between two glucose isotopomers, as a proxy for de novo lipogenesis, was greater in LF caIves ( 12.9%) than in HF calves ( 1.4%), indicating incrcased fatty acid syntbesis from glucose in LF caIves. Expression of genes involved in fatty acid synthesis, desaturation and elongation, and triacylglycerol synthesis was greater in LF calves than in HF calves, and this was most pronounced in retroperitoneal adipose tissue. ln conclusion, these findings indicate that caIves are able to synthesize fatty acids from glucose when a low-fat milk replacer is fed.