Effect of reduced dietary protein level on energy metabolism, sow body composition and metabolites in plasma, milk and urine from gestating and lactating organic sows during temperate winter conditions

•Feed intake capacity is limiting for milk production of organic gilts during winter•No effect of 12% reduced dietary protein on sow performance during gestation•Low protein ensured adequate lysine intake in gestation but not during lactation•Insufficient feed intake caused > 1 kg/d of fat mobilization from d5-d20 in lactation•Total ME requirement of outdoor pregnant organic gilts in winter was ~ 68 MJ ME/d•Total ME requirement of organic lactating first parity sows was ~ 153 MJ ME/d Energy spent on thermoregulation and the opportunity for increased locomotive activity increases the energy requirements of outdoor relative to indoor housed sows, whilst their protein requirement most likely is comparable on a daily basis. The purpose of this study was to quantify the energy needed for maintenance, maternal retention, milk production, thermoregulation and increased locomotive activity in organic sows. A total of 47 gilts (Landrace x Yorkshire; 190 kg at insemination) were reared outdoor under organic conditions for five months during winter. To study dietary effects of protein, gilts were fed one of two iso-energetic compound feeds, where dietary protein differed by 12%. Gilts had ad libitum access to grass clover silage and were fed similar amounts of metabolisable energy (ME) from compound feed equivalent to the energy recommendations for indoor sows + 15% in both groups. Collection of plasma and urine was performed on d60 and d100 of gestation and plasma, urine and milk was collected on d5, d20 and d40 of lactation. On all collection days, sows and piglets (n=635) were weighed individually, sows were back fat scanned and heartrate and locomotive activity was registered with a tracking system. Sow body composition was estimated using the deuterium dilution technique. Live weight and back fat thickness were not affected by the dietary protein level, neither was the number of total born, still born, piglet birth weight or piglet weight gain until weaning at seven weeks (14.5 kg). There was no effect of protein level on locomotive activity. Milk yield peaked with 12.9 kg/d around d20. In total, 58% of the gross energy intake was associated with milk production at d20 including heat. Milk energy output was 69 MJ ME/d at peak lactation at d20. Sows fed the low protein compound feed had a lower milk yield from d20 to d40 as compared with control fed sows (8.0 vs.10.3 kg/d; P