Twenty four lactating Zaraibi goats in mid lactation were used in a 2 x 2 factorial experimental design to evaluate two different sources of ruminally
degradable non structural carbohydrates (high and low RDNSC) and two different sources of ruminally degradable protein (high and low RDP). Four experimental diets were formulated to study their effects on some rumen fluid parameters and microbial activities. The obtained results showed that high RDP as well as RDNSC gave
significant (P<0.05) higher values of pH. A significant (P<0.05) reduction in NH₃-N concentrations recorded with diets contained low RDP without significant differences due to RDNSC sources. No significant differences were noticed between VFA concentrations among the tested diets, except that contained high RDP with low RDNSC which gave the highest significant (P<0.05) value. It seems that the conditions in rumen environment from pH, NH₃-N and VFA concentrations was favorable for coccid form bacteria to dominate the bacterial population and the bacterial growth (TBC or OD) which was clearly reflected on the enzymatic activities, since most enzymatic activities recorded for cellulolytic group. On the other hand, the gas volume measured was higher with amylolytic and proteolytic bacterial groups than cellulolytic ones indicating for the utilization of high RDNSC and low RDP in the rumen of experimental animals. This means that bacterial groups in the rumen utilized the tested sources of RDP and RDNSC in the manner that kept most nutrients to be utilized in the lower part of digestive system. This explanation could be reasonable since the results support the energy values of tested diets which showed the superiority of low RDP with high RDNSC containing diet. Microbial protein synthesis in the rumen fluid was significantly (P<0.05) affected by RDNSC more than RDP. The highest DNA, RNA and ON values were obtained when goats fed low RDNSC with high RDP. From the above mentioned results the present study came to the conclusion that feeding low RDP with high RDNSC would be of beneficial effect on rumen environment and its bacterial activities. Since the diet contained high RDP with low RDNSC tended to give better values of rumen parameters and bacterial activities as well as microbial protein synthesis it is recommended under similar experimental conditions to use soybean meal with corn to improve the nutritive value of diets for lactating goats.