A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN TROPICAL ANIMAL PRODUCTION OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA.A study was conducted to validate the use of rumen liquor from slaughtered cattle as an alternative source of inoculum for estimation of in vitro digestibility of ruminant feedstuffs. The experiments were conducted in three (3) different institutions, namely Sokoine University of Agriculture (SUA), Tanzania, National Livestock Resources Research Institute (NALIRRI) Uganda and Rwanda Agricultural Board (RAB) in Rwanda. Each institution evaluated 4 diets of different nutritional quality. The dry matter digestibility (DMD) and organic matter digestibility (OMD) of the diets were determined using in vivo total collection method and in vitro two stage technique of Tilley and Terry (1963). The in vivo experiment was conducted using four rumen fistulated steers which were allocated to the 4 diets for 4 periods in a 4 x 4 Latin square design. The in vitro technique followed 2 x 4 factorial arrangement in which the 4 diets were incubated in 2 different sources of rumen liquor; that is rumen liquor collected from fistulated and from slaughtered cattle. The obtained in vitro results using rumen liquor from fistulated and slaughtered cattle from all institutions were regressed against those determined by in vivo technique to derive prediction equations. The rumen liquor collected from the experimental animals at SUA was assessed for pH and concentrations of ammonia nitrogen (NH3-N) and total volatile fatty acids (VFAs). The pH value (6.59±0.06) of the rumen liquor from fistulated cattle was not different (P > 0.05) from that of slaughtered cattle (6.53±0.06). Rumen liquor from slaughtered cattle contained higher (P < 0.05) concentration of rumen NH3-N (122.74 ± 1.71 versus 111.34 ± 1.71 mg/l) and total VFAs (151.84 ± 7.75 versus 124.04 ± 7.75 mmoles/l) than that from fistulated cattle. The in vivo DMD of the different diets at SUA ranged from 51.6% - 61.8% while in vivo OMD ranged 51.4 – 62.2% and were both significantly (P < 0.05) different. There was no significant difference (P > 0.05) on the in vivo DMD and OMD of the diets used at NALIRRI. The in vivo DMD of the diets used at RAB ranged from 84.7% - 90.5% and in vivo OMD ranged from 82.1% - 87.9% and they were both significantly (P < 0.05) different and relatively higher than the values obtained from the other institutions. The in vivo DMD and OMD of the diets in all institutions were significantly (P < 0.05) higher than the in vitro values obtained using rumen liquor from fistulated and slaughtered cattle. The in vitro DMD (42.6%) and OMD (38.8%) obtained using rumen liquor from slaughtered cattle at SUA were significantly (P < 0.05) higher than those obtained using rumen liquor from fistulated cattle (DMD = 40.0% and OMD = 36.2%). In the other institutions, there was no significant difference on the values of in vitro DMD and OMD obtained using rumen liquor from the two sources. There was also no significant difference (P > 0.05) on the prediction equations when rumen liquor from fistulated or slaughtered cattle is used in in vitro technique for predicting in vivo DMD and OMD. From this study it is concluded that, rumen liquor from slaughtered cattle may be used for estimating in vitro digestibility of ruminant feedstuffs.