INFLUENCE OF GROWING-SEASON, TANNIN CONTENT AND AUTOCLAVE TREATMENT ON THE NUTRITIVE-VALUE OF NEAR-ISOGENIC LINES OF FABA BEANS (VICIA-FABAL.) WHEN FED TO LEGHORN CHICKS

1. The objective of this study was to determine the influence of heat- treatment (autoclaving) on the utilisation by chicks of near-isogenic lines of faba beans that were either tannin-free (Winter-white or Spri ng-white) or had tannins in the seed coat (Winter-coloured or Spring-c oloured). The effect of heat treatment on a common tannin-containing c ultivar, Diana, was also studied. 2. The nitrogen-corrected apparent m etabolisable energy (AME(n)) values of diets containing 600 g faba bea ns/kg diet were affected by tannin content and autoclave treatment of faba beans, with 59% of total variance in AME(n) being attributable to the effect of autoclaving. The AME(n) values were 9% higher for chick s fed on the autoclaved compared with those fed on diets containing th e raw faba beans, 5% higher for the near-isogenic faba beans with no t annins compared with those with tannins, and 4% higher for the Winter compared with the Spring cultivars. 3. The above study was carried out on droppings obtained by total collection. Similar but not identical trends were obtained when AME(n) was calculated using the chromic oxid e index method (r = 0.91). 4. Both autoclaving and the use of tannin-f ree faba beans improved the apparent protein digestibility (APD) of th e diets by similar amounts (4% as determined by the total collection m ethod and 6% as determined by the chromic oxide index method). 5. The digestibility of most amino acids either alone or together was affecte d by a cultivar X tannin X processing interaction. The cultivar by tan nin interaction demonstrated that autoclaving increased the digestibil ity of amino acids to a greater degree when the tannin-containing (for example, 9% for lysine) than when the tannin-free faba beans (4% for lysine) were used in the diets. 6. The improvements in AME(n), APD and total amino acid digestibilities of faba beans following heat treatme nts ranged from 18% to 33%, 5% to 16% and 5% to 11%, respectively. The results demonstrate that the method of analysis can affect the values obtained but that they do not change the overall pattern of results. The results also suggest that, in most cases, more than half of the re sponse to heat treatment is associated with the inactivation of tannin s while the balance of the response is attributable to an effect of he at treatment on the non-tannin-containing factors. In summary, heat tr eatment can improve the utilisation of faba bean by chickens especiall y when they contain tannins. 7. Chicks, unlike rats, do not seem to ad apt to tannins as the excretion of 3 amino acids that are the main con stituents of a proline-rich protein were not affected by dietary tanni ns.