Microbial protein net synthesis in sheep fed hay-concentrate diets supplemented with different source and level of fat

Three experiments in a 4 x 4 Latin square design were carried out on four r ams fitted with rumen cannulas to investigate the effect of varying sources and levels of fat addition on microbial protein net synthesis (MN) in shee p fed a concentrate-based diet (60% of concentrate and 40% of meadow hay). In the 1(st) experiment addition of rape seed oil (RSO) was tested, linseed oil (LSO) was added in the 2(nd), and tallow (TAL) in the in 3(rd) experim ent. Treatments in all experiments were similar: a control group without fa t addition and experimental groups with 4, 8 and 10% of fat in DM of the di et. Microbial production in the rumen, purine derivatives in urine, ruminal ammonia, pH, fatty acids in the rumen were measured. In all cases fat addi tion resulted in decreased MN, however, 8% fat supplementation had the leas t deleterious effect on MN production. Fat addition significantly affected purine derivatives excretion. LSO as the supplemental fat led to a decrease in N ammonia concentration from 7.8 mmol/L in the control group to 6.39 mm ol/L in the group that received 8% LSO, whereas a significant increase to 9 .00 mmol/L was observed when 10% LSO in DM was fed. Ruminal fluid pH was no t altered by treatments. In all of the experiments, the increased fat conte nt in the diets decreased the molar percentage of acetic acid. Supplementat ion of the diet with LSO and TAL resulted in an increase of the propionic a cid level (P<0.05).