PREDICTING THE STEADY-STATE ATTAINABILITY OF FECAL EXCRETION IN RUMINANTS WHEN RELATED TO LENGTH OF PRELIMINARY PERIOD AND FLOW-RATE OF DIGESTA

The steady-state attainment of faecal excretion in ruminants given a n ew feed was predicted by the attainability coefficient calculated usin g the Blaxter's compartmental model containing three parameters: lengt h of preliminary period, outflow rate from rumen (k(1)) and flow rate through hind-gut (k(2)) of digesta. It was theoretically predicted tha t the faecal excretion approached a steady-state closer when the lengt h of adaptation period was longer and/or the rate of digesta movement was higher. After the change of feed, the coefficient calculated for t he faecal excretion derived from a previous feed showed a decrease to approach a zero-state closer when the longer period had passed and/or the digesta moved faster. Taking 28-day preliminary period led to the attainability coefficient higher than 0.99 irrespective of flow rate, meaning that a steady-state was attained for faecal excretion. Seven-d ay adaptation gave a value higher than 0.96 to the steady-state attain ability provided both k(1) and k(2) were higher than 0.03. The applica tion of the steady-state attainability to several published studies of various feeding conditions showed that the coefficient higher than 0. 99 was given to almost all the cases in which 7-32 day adaptation was taken and flow rate was 0.014-0.085 for k(1) and 0.031-0.503 for k(2). The prediction was also applied to several other published studies wi th tropical forages where only k(1) was estimated to be 0.019-0.085 an d 7-day adaptation gave a value higher than 0.94 to the steady-state a ttainability of most cases. It is suggested that the steady-state atta inment of faecal excretion in ruminants may be predicted by the attain ability coefficient calculated using the Blaxter's model.