AbstractThe effect of two dietary electrolyte balance (dEB, Na⁺ + K⁺ – Cl^-) levels (–135 and 145 mEq/kg diet) on heat production, energy and nitrogen retention in piglets was assessed. The experiment consisted of a 13-day adaptation period and a 7-day balance period in two open-circuit climate respiration chambers. Nine groups of three (4 weeks old) crossbred barrows were assigned to one of two diets (five and four groups for –135 and 145 mEq/kg dEB diets respectively). During the balance period, diets were provided at 2·3 times the energy requirement for maintenance in two equal meals daily. Total heat production for each group was determined every 9 minutes from the exchange of CO₂ and O₂. Faeces and urine mixture was quantitatively collected during the balance period to measure energy and nitrogen balance. Total heat production and metabolizable energy costs for maintenance tended (P 0·10) to be higher in the 145 mEq/kg dEB group (681 and 443 kJ/kg^0·75 per day respectively) than in the –135 mEq/kg dEB group (660 and 412 kJ/kg^0·75 per day respectively). Differences in total heat production between the two dEB groups mainly occurred in the daytime (light period), when significance level was P 0·01. The respiratory quotient and energy retention as fat were numerically (but not statistically significantly) lower in the 145 mEq/kg dEB group compared with –135 mEq/kg dEB. In conclusion, energy balances were similar for both treatments. However in the daytime (light period), piglets needed more energy for maintenance after ingesting a diet with a dEB level of 145 mEq/kg compared to a diet with a dEB level of –135 mEq/kg at a restricted feeding level.