Heat production by fattening pigs in deep-litter or conventional slatted floor sys- tems. The insulation and ventilation requirements for livestock buildings depend on the amount of heat and water vapour produced by the animals. Our knowledge of heat production in slatted floor build- ings must be adapted to the deep-litter system, in which there is early composting of the slurry. We isolated the effect of the husbandry system on heat and water vapour production using the same building, animals and external temperature. We compared the amount of heat and water vapour pro- duced with the deep-litter system to that predicted by models, and to that of a conventional slatted floor system, used as a reference. Twelve pigs were fattened in two identical 14 m animal enclosures, with natural ventilation, and with external and internal temperatures kept constant (13 °C and 23 °C). The total, sensible and latent heat productions were measured for the deep-litter housing during growing-finishing pigs and were equal to 302, 127 and 176 W, respectively. The litter produced a large