Energy and Nitrogen Evaluation of Swine Diets Containing Added Fat or Corn Cobs

Twelve pigs weighing approximately 52 kg. were used to determine the digestible and metabolizable energy content, the TDN value and nitrogen balances on complete swine diets containing 16% protein and varying energy content. The results showed that the gross energy level of the diet had little influence on the digestibility of the diet components except that the digestibility of either extract increased when the level of fat in the diet increased. The addition of 10% corn cobs to the diet significantly decreased the digestibility of dry matter, nitrogen-free extract, and ether extract (P<.01) and protein (P<.05). The addition of animal fat to the diet decreased, but not significantly, the amount of nitrogen stored over a 5-day balance period, but did not influence the percent of nitrogen retained. The addition of corn cobs did not influence the amount or percent of nitrogen retained during a 5-day balance study. Determined metabolizable energy values were in close agreement with values determined by Diggs et al. (1965) for the young pig, and were similar but 3 to 6% higher than calculated values based on the metabolizable energy values presented by Titus (1955) for poultry. Digestible energy values reflected energy concentration of the diet ingredients while the energy loss through the urine was relatively constant, amounting to approximately 3% of the gross caloric content of all diets. It is estimated that 10% added corn cobs were undigested by 52 kg. swine and that the cobs increased the fecal N excretions by 10% and reduced the DE of the basal diet by a maximum of 5%. The fat used was approximately 88% digestible and did not reduce the utilization of other nutrients studied. It was estimated to contain approximately 8,200 kcal. DE per kilogram. The other data presented generally confirm the validity of using 4,400 kcal. of digestible energy per kg. of TDN as a conversion factor. Slightly lower values should be used if diets contain added fat.