Effects of cold exposure on digestion, microbial synthesis and nitrogen transformations in sheep

Abstract

1. Six closely shorn sheep were given brome grass (Bromus inermis) pellets at the rate of 59 or 98 g dry matter (dm)/h and maintained at ambient temperatures of 2–5° and 22–25° for 35 d. Measurements of digestion, rate of passage of digesta, and nitrogen transformations were made during the last 13 d of temperature exposure.2. Cold exposure at the lower level of intake reduced the apparent digestibility of dm and organic matter (om) approximately 0.055 units. Apparent digestibility of dm and om was further decreased approximately 0.03 units with the higher level of food intake in the cold. Apparent N digestibility was significantly depressed from 0.62 to 0.59–0.60 for sheep exposed to cold at both levels of intake.3. Exposure of sheep to cold resulted in a decrease in the turnover time of the particulate marker, 103Ru, from 19 h to 10.12 h in the rumen, a decrease in rumen volume, and a significant increase in dm and om which escaped digestion in the stomach. Volatile fatty acid and methane production in the rumen were highly correlated with the amount of om digested in the stomach. Methane production in the rumen comprised 0.81 of total production in warm sheep, and 0.68–0.74 of total production in cold-exposed sheep.4. More om and non-ammonia-N were apparently digested in the intestines of sheep exposed to cold than in warm sheep at the same food intake, but the apparent digestibilities in the intestines of dm, om and non-ammonia-N leaving the abomasum did not change significantly between treatments. The retention time of 103Ru in the intestines was 17.18 h in sheep given 59 g dm food/h at both exposure temperatures, but was reduced to 12 h for cold-exposed sheep given 98 g dm/h. Methane production in the postruminal tract was increased at the higher food intake, but there was no difference between warm and cold-exposed sheep at the same food intake.5. The rate of irreversible loss of plasma urea and rumen ammonia was measured by infusion of [15N]urea and [15N]ammonium chloride. Exposure to cold reduced the irreversible loss of plasma urea from 0.85 to 0.75–0.77 g N/g N intake, and the irreversible loss of rumen ammonia from 0.66 to 0.57–0.61 g N/g N intake. The transfer of plasma urea-N to the rumen ammonia pool was significantly greater (9.5 g N/d) in the cold-exposed sheep than the value (7.3 g N/d) in warm sheep.6. The efficiency of microbial synthesis in the rumen was increased in cold-exposed sheep, and was related to the amount of N recycled through the rumen ammonia pool from intraruminal sources. The effect of dilution rate and fermentation patterns on efficiency of microbial synthesis is discussed.

Tissue responsiveness and sensitivity to insulin in sheep fed plantain and orchardgrass and exposed to cold

“…Similar results were observed in sheep fed fresh PL and OR diets (Sano et al 2002). The tendency toward reduced BW during cold exposure may mainly be due to reduced digestibilities and water intake and enhanced energy expenditure (Kennedy et al 1976;Kennedy & Milligan 1978;Tsuda et al 1984) because feed intake was the same in both environments. Crude protein intake was estimated to be similar between the PL and OR diets (Tables 1 and 2).…”

Influence of substrate and microbial interaction on efficiency of rumen microbial growth

“…This complexity is further increased by changes in C and k with time after feeding because of decreasing particle size with progressive digestion and changes in saliva flow. Compartment B may serve as a transport or shuttle compartment between A and C (Czerkawski, 1984 (Kennedy et al, 1976 ;Kennedy and Milligan, 1978 ;Harrison et al, 1975) (fig. 2) (Faichney and Griffiths, 1978 Zinn and Owens (1983).…”

Effect of vasoactive intestinal polypeptide and environmental temperatures on feed intake, digesta flow and nutrient digestion in sheep

“…The present study with ad libitum-fed sheep showed that there were increases (P < 0.05) of rates of duodenal passage of DM, CP, OM, AA and microbial protein in the cold, compared to a thermoneutral environment. Although similar results have been reported for animals on restricted intakes (Kennedy and Milligan 1978;Kelly et al 1989), this is the first comprehensive study of this type in ad libitum fed sheep. The increased passage of nutrients into the small intestine is presumably related to enhanced forestomach motility (Titchen 1968;Christensen et al 1991;Miaron and Christopherson 1992), but it may also be secondary to increased feed intake induced by the energy demand of the environment.…”

“…An enhanced digesta flow often improves synthetic efficiency of ruminal bacteria (Kennedy et al 1976;Kennedy and Milligan 1978;Mathison et al 1995). Indeed, the increased (P < 0.05) quantitative contributions of microbial protein to the duodenal AA supply was realized by higher digesta flow induced by cold exposure in the present study.…”