Energy requirement of growing pigs under commercial housing conditions

Scientifically derived recommendations for the energy supply to growing pigs are generally based on estimates of the metabolisable energy (ME) requirements for maintenance (MEm) and protein (MEp) and fat (MEf) retention. It is supposed that animals are kept within the zone of thermoneutrality and that their physical activity is not elevated. These assumptions might not always be true for practical housing conditions, and it is difficult to quantify the additional energy needed for thermoregulation and physical activity. Hence, at a given ME intake, differences can occur between the actual growth rates and those predicted from the recommendations. To quantify such differences, three trials were carried out under commercial farming conditions with pigs growing from 25 to 120 kg body weight (BW). In each trial, 624 castrated male and female pigs were allocated to four feeding groups distributed over 24 double pens. The rations were provided according to the animals' feed intake capacity and BW was recorded every three weeks. Protein, fat and energy retention (RE) was derived from carcass composition and BW gain. The difference between ME intake and MEm plus ME required for growth (MEg = RE/kpf) was calculated and seen as the ME required for purposes other than maintenance and growth (MEx). MEx accounted for 2.0%, 17.0% and 21.4% of the animals' ME intake in Trials 1, 2 and 3, respectively, and was higher in female than in castrated male pigs when related to metabolic BW. It was concluded that total ME requirements of pigs kept under commercial housing conditions can be considerably higher than ME requirements predicted from feeding standards since they usually ignore MEx. MEx can be used as an indicator for the quality of housing systems. Further studies are needed to identify the key factors responsible for MEx to allow for more precise recommendations for the energy supply to commercially raised pigs.