EFFECTS OF ANHYDROUS AMMONIA TREATMENT OF WHEAT STRAW AND STEAM COOKING OF ASPEN WOOD ON THEIR FEEDING VALUE AND ON RUMINAL MICROBIAL ACTIVITY .2. FERMENTABLE ENERGY AND MICROBIAL-GROWTH DERIVED FROM AMMONIA NITROGEN IN OVINE RUMEN

Concentrations and rates of production of volatile fatty acids (VFA) were determined in incubated whole rumen digesta (WRD) samples from 4 fistulated sheep fed 5 rations, one at a time, to all sheep. Simultaneously, WRD samples were incubated with ammonia-15N to determine N uptake and microbial growth derived from ammonia-N. Microbial growth derived from ammonia N was not affected by roughage treatment and none of the parameters related to microbial utilization of ammonia-N followed patterns related to gains of lambs fed the same rations. Rumen microbes were capable of adjusting ammonia-N uptake to maintain fairly constant assimilation and have an ability to scavenge N from ammonia pools very much reduced in size and that nitrogenous substances other than ammonia can be utilized extensively for microbial synthesis. Volatile fatty acid concentrations, rates of production and patterns of individual VFA production were reasonably consistent with liveweight gains, indicating that patterns of VFA production, in addition to being indicative of microbial response to available substrate, may also be useful indicators of ration feeding value. The VFA patterns obtained with the treated wood were similar to those characteristic of high roughage rations, while the patterns resulting from feeding the ammonia-treated straw were similar to those usually obtained only with diets containing substantial amounts of readily fermentable carbohydrates from grain.