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

Abstract

Three experiments in a 4 x 4 Latin square design were carried out on four rams fitted with rumen cannulas to investigate the effect of varying sources and levels of fat addition on microbial protein net synthesis (MN) in sheep 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 experiment. Treatments in all experiments were similar: a control group without fat addition and experimental groups with 4, 8 and 10% of fat in DM of the diet. Microbial production in the rumen, purine derivatives in urine, ruminal ammonia, pH, fatty acids in the rumen were measured. In all cases fat addition resulted in decreased MN, however, 8% fat supplementation had the least 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 mmol/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 not altered by treatments. In all of the experiments, the increased fat content in the diets decreased the molar percentage of acetic acid. Supplementation of the diet with LSO and TAL resulted in an increase of the propionic acid level (P<0.05).

A note on the effect of energy sources on duodenal flow of fatty acids and bacterial nitrogen in sheep

“…The results of the experiment carried out by Hussein et al (1996) also indicated that fat supplementation from canola seed (at 5% of dietary DM), in either form, had no effects on ruminal N metabolism or flows of amino acids to the duodenum and suggest that treated whole canola seed may stimulate ruminal bacterial protein synthesis. In our previous experiment on sheep given different energy sources, we did not find a deleterious effect of fats on microbial synthesis, which tended even to be slightly higher than in animals fed control diets (Szumacher-Strabel, 1998). These results indicate that the energy available from the control diet was not a limiting factor for microbial synthesis in the rumen.…”