The relationship between variations in in vitro microbial biomass production and microbial protein
supply to the host animal was examined in 13 Malawian goats fed on stover leaves from two varieties
of maize at Bunda College, Malawi, in 1995. The in vitro parameters were analysed based on the
concept of the partitioning factor (PF) which is obtained by the combination of gas volume
measurements with determinations of the amount of substrate truly degraded. The PF reflects
substrate-dependent variation in the in vitro partitioning of degraded substrate between short chain
fatty acids (SCFA), gases and microbial biomass. The in vivo microbial protein synthesis was
estimated by the urinary excretion of the purine derivatives (PD) allantoin, uric acid and xanthine +
hypoxanthine. For the two types of stover leaves examined, the higher microbial efficiency of one
variety in vitro was reflected by different PD excretions on practically identical digestible dry matter
intakes in vivo. It is concluded that substrate-dependent variations in microbial efficiencies as detected
by the PF are also evident and relevant for in vivo microbial protein synthesis.