Effect of energy level in lactating sows on yield and composition of milk and nutrient balance of piglets.

The effects of energy level on milk yield, milk composition and growth of the piglets were studied in 20 gilts (10 replicates of two littermates) and their litters during a 21-d lactation. The metabolizable energy (ME) levels were 14.2 and 10.4 Mcal ME X d-1 X sow-1 in the high energy (HE) and low energy (LE) groups, respectively. The daily supply of other nutrients in the diets was identical in both treatments. Milk yield measured every 4 d was lower in the LE group. But fat (8.0 vs 6.9%), energy (1.27 vs 1.14 Mcal/g) and nitrogen (.78 vs .74%) contents of milk were significantly higher in the LE gilts compared with the HE gilts. The daily output of energy and nitrogen was therefore equivalent in both treatments (respectively, 8.28 Mcal and 51.8 g/d), but the fat output was higher in the energy-restricted gilts (532 vs 490 g/d). Growth rate of the litter was similar in both treatments, but piglets suckling LE dams had higher dry matter, fat and energy contents in their body at weaning. Piglets retained 89, 54 and 55% of nitrogen, fat and energy, respectively, of milk between birth and weaning. The results suggest that the ability of sows to mobilize body lipids in order to maintain the output of energy in milk is reduced as body fat reserves are depleted.