[Energy utilization of retrograded starch by sows].

A total metabolism trial was conducted in eight adult sows to compare the energetic utilization, nitrogen balance, and passage rate of retrograded starch (RGS) with that of pregelatinized wheat starch (PWS). The starch was added at levels of 12 and 24 g/kg W0.75 to a basal ration that covered the maintenance requirement. Each animal received all four treatment combinations in a change-over design. At the start and end of the trial all sows were fed the basal ration alone. Feeding took place twice daily. During each 3-week metabolism period a complete balance measurement was performed for all animals, with 6 daily collections of feces and urine and a 48-h gas exchange measurement in a respiration chamber. The sows' heat production and energy retention were calculated by the carbon-nitrogen balance method and the RQ method. Digestibility and metabolizability of energy and energy retention were lower in the basal ration with RGS supplement than in the PWS supplemented ration. With regard to N exchange, sows supplemented with RGS excreted more N in the feces and less N in the urine, whereas N retention was equal with both rations. The production of CH4 was higher with RGS than after feeding pregelatinized wheat starch. When compared with the nonsupplemented basal ration, the fecal volume was unchanged with PWS but significantly increased with RGS. The feed passage, measured as the mean retention time of a marker in the digestive tract, was 86 h on the basal diet, falling to 75 h with PWS supplementation and 65 h with RGS. The utilization of the supplemented energy was 12% lower for RGS compared with PWS. This difference was due to a reduction in the digestibility and intermediate utilization of the energy. The amount of metabolizable energy was calculated as 16 kJ/g and the net energy as 12.5 kJ/g RGS. The results of the trial underline the importance of retrograded starch as a fiber type nutrient and the associated advantages for the bowel function. The energetic utilization on the other hand is only slightly lower than that of non-resistant starch; unlike pure fibrous feed materials, RGS can therefore not be regarded as a "low energy" substance.