Effect of pressure toasting on the rumen degradability and intestinal digestibility of whole and broken peas, lupins and faba beans and a mixture of these feedstuffs

Abstract

The effects of pressure toasting of whole and broken peas, lupins and faba beans on in situ degradability of protein and starch and intestinal digestibility of protein were studied. To test for associative effects on rumen degradability and intestinal digestibility after toasting, a mixture of peas, lupins and faba beans was examined and results were compared with weighted averages of separately processed feedstuffs. Pressure toasting for 3 min at 132°C decreased in situ protein degradability of peas, lupins and faba beans and in situ starch degradability of peas and faba beans, especially when broken versus whole seeds were processed. Undegraded intake protein (%UIP) increased after toasting whole or broken seeds from 25% to 44% and 52% for peas, from 22% to 47% and 51% for lupins and from 20% to 48% and 57% for faba beans, respectively. Undegraded intake starch (%UISTA) increased from 39% to 50% and 53% after toasting whole and broken peas and from 33% to 53% and 60% for toasted whole and broken faba beans, respectively. Total tract protein digestibility, measured after 12 h rumen and subsequent intestinal incubation, remained unchanged for peas and faba beans, but decreased from 99% to 98% for toasted whole lupins and to 97% for toasted broken lupins. For toasted whole and broken faba beans, pressure toasting increased %UISTA from 33% to 53% and 60%, respectively. After pressure toasting, washable fractions ( W) of all legume seeds decreased for both constituents, the fractional rate of degradation ( k d) of protein decreased, while the k d of starch increased. It was concluded that protein degradability decreased after pressure toasting, without seriously affecting its total tract protein digestibility. Toasting a mixture of peas, faba beans and lupins resulted in higher starch degradabilities than expected, based on the separately treated feedstuffs. The k d's of the mixtures were higher than expected: 5.49 versus 4.29% h −1 for whole seeds and 5.01 versus 4.18% h −1 for broken seeds, respectively. Consequently, %UISTA was lower than expected (47% vs. 51% for whole seeds and 50% vs. 57% for broken seeds).