Intensive piggeries are generally large warehouse-like buildings or barns. Indoor pig systems allow the pigs' conditions to be monitored, ensuring minimum fatalities and increased productivity. Buildings are ventilated and their temperature regulated. Most domestic pig varieties are susceptible to sunburn and heat stress, and all pigs lack sweat glands and cannot cool themselves. Pigs have a limited tolerance to high temperatures and heat stress can lead to death. Maintaining a more specific temperature within the pig-tolerance range also maximizes growth and growth-to-feed ratio. Indoor piggeries have allowed pig farming to be undertaken in countries or areas with unsuitable climate or soil for outdoor pig raising. In an intensive operation, pigs will no longer need access to a mud, which is their natural cooling mechanism. Intensive piggeries control temperature through ventilation or drip water systems