The effect of either raw or boiled liquid extract from potato (Solanum tuberosum) on the digestibility of a diet based on barley in pigs

The nitrogen (N) of raw potato is poorly digested by the pig and the hypothesis tested in the experiment was that this is due to an anti‐nutritive substance present in the tuber and not simply due to the physical inaccessibility of much of the potato protein to enzyme attack or to the protein of the potato being refractory to gut enzymes. Four growing pigs, each fitted with an ileal cannula were fed on a basal diet of barley plus minerals and vitamins to which was added minced raw potato (RP) or a liquid extract of potatoes which was either freeze‐dried (LE) or boiled and concentrated (BE). These materials each contributed 12 g N day−1 for each pig. Each pig was given 2.1 kg organic matter (OM) day−1. In diet RP 25.5% of this was from potato compared with 7.2 and 7.8% in diets LE and BE, respectively. The digestibility of N determined at the terminal ileum was reduced with RP by 9.5% (NS) and with LE by 23% (P<0.01) while BE increased it by 24.7% (P<0.01) compared with the coefficient of digestibility for the N of the barley diet. The digestibility of OM was significantly (P<0.001) reduced by 9.5% with RP but with LE and BE it was similar to the control value. Over the whole gut, coefficients for N changed by −19.8% (P<0.001), −4.7% (NS) and +9.0% (P<0.05) when RP, LE or BE, respectively were included in the basal diet. Corresponding changes in OM were +2.4% (NS), +1.9% (NS) and +3.6% (P<0.05). It is suggested that the anti‐nutritive factor in potatoes should be denatured by appropriate treatment to improve the digestibility of dietary protein.