The need to complement in vitro gas production measurements with residue determinations from in sacco degradabilities to improve the prediction of voluntary intake of hays

The need to complement in vitro gas production measurements with residue determination is demonstrated by the recalculation and reassessment of published data on in vitro gas production, in sacco degradabilities and voluntary dry matter intake (DMI). The in sacco degradability - gas volume ratio was determined at 24 and 48 h of incubation, termed partitioning factor (PF) and combined with rate and extent parameters of in sacco degradability and in vitro gas production to predict DMI. Ln vitro gas production and in sacco degradability characteristics (a + b) and c as described by the equation y = a + b(1-e(-ct)) explained 0.373 and 0.668 respectively of the variation in DMI of 19 legume and grass hays. The complementation of gas production parameters by the PF24 increased the R(2) value to 0.744 with PF24 accounting for 0.407 of the variation in DMI, the rate of gas production (c) for 0.218 and the extent of gas production (a + b) for 0.119 of the variation in DMI. As a single parameter, PF48 showed the highest correlation (R(2) = 0.597) with DMI but the combination of PF48 with rate and extent of in sacco or in vitro gas production measurements did not improve the correlation further, probably due to an intercorrelation between rates of fermentation and PF48. Hays which were degrade at faster rates had higher PF values indicating proportionally higher microbial yield and lower short-chain fatty acid production per unit substrate degraded. Generally, hays with high in sacco degradabilities but proportionally low gas production i.e. hays with high PF values showed higher DMI.