DEGRADABILITY OF FROZEN AND ENSILED ALFALFA PROTEINS BY SHEEP AND ASSESSMENT OF DUODENAL DIGESTA PROTEIN

Six adult ewes equipped with ruminal and duodenal cannulae were used i n a crossover experiment to determine the effect of ensiling alfalfa o n protein degradation in vivo. Frozen alfalfa and wilted silage prepar ed from the same crop were fed twice a day (08:00 and 16:00 h) with a mineral supplement. Water was available free choice. Rumen digesta out -flow rate and duodenal microbial nitrogen (N) were estimated using ch romium mordanted alfalfa and RNA respectively. Animals fed frozen alfa lfa had significantly higher (P<0.05) duodenal non-ammonia N (g day(-1 )), Ensiling alfalfa did not alter ruminal degradation of forage N, th e passage of duodenal microbial N (g day(-1)) and the apparent efficie ncy of microbial N synthesis in the rumen (g kg(-1) organic matter app arently digested in the rumen). Plasma levels of branched chain amino acids in ewes fed frozen alfalfa were significantly higher (P<0.05) th an in ewes fed silage. There were no treatment differences (P>0.05) in the composition of amino acids flowing to the duodenum. Attempts to i dentify proteins entering the duodenum indicated the presence of only low molecular weight proteins below 40 kDa for sheep fed frozen alfalf a and largely below 18 kDa for sheep fed silage. The results obtained indicate that alfalfa protein is a source of highly degradable protein with 13% and 10% undegradable protein in frozen and ensiled alfalfa r espectively, and sheep fed alfalfa silage diets had less intestinal am ino acid absorption compared with those fed frozen alfalfa.