The effect of cold exposure of sheep on digestion, rumen turnover time and efficiency of microbial synthesis

Abstract

Six closely shorn sheep were given brome grass (Bromus inermis) pellets at 1 h intervals and maintained at ambient temperatures of -1 to 1.degree. and 18-21.degree. for 28 days. Measurements of digestion were made during the last 10 days of temperature exposure. Cold exposure resulted in a reduction in apparent dry matter (DM) digestibility from 0.482-0.450, and of apparent digestibility of organic matter (OM) from 0.511-0.477. Neither apparent digestibility nor retention of nitrogen was affected. Apparent digestibility of OM in the rumen decreased from 0.300 to 0.242 with cold exposure, and was highly correlated with turnover time in the rumen of 103Ru, which was used as a particulate marker. The efficiency of microbial synthesis (g N incorporated into microbial cells/kg OM apparently digested) was correlated with the dilution rate of the solute marker (51Cr) and with the turnover time of the particulate marker (103Ru) in the rumen. Digestion in the intestine of DM and OM accounted for significantly more apparent digestion in the whole gastrointestinal tract for sheep kept in the cold than for sheep kept in the warm. The apparent digestibilities of DM and OM entering the intestines were similar in sheep on both treatments, but significantly more non-ammonia-N was digested in the intestines of cold-exposed sheep. The influence of dilution rate of rumen fluid on the efficiency of synthesis of microbial cells in the rumen is discussed.