Forage particle breakdown and movement in the reticulo-rumen in cattle and interactions between cold exposure and diets in sheep

Sheep, fitted with cannulas in the rumen and proximal duodenum, were given different diets as well as different physical forms of diets. The sheep were closely shorn and exposed to ambient temperatures of 22 deg. C to 24 deg. C (warm) or 1 deg. C to 5 deg. C (cold). Measurements of rates of passage, digestibility, rate of transfer of plasma urea to the rumen, feed protein degradation, microbial protein synthesis and rate of rumen fermentation were determined. The effect of cold exposure on digestion was not dependent on the physical form of the diet given at a fixed intake, but was associated with the type of diet (hay, concentrate). The greater voluntary intake was a result of increased clearance of digesta from the rumen through decreased particle size and increased frequency of reticulum contractions. The apparent digestibility of organic matter and nitrogen was reduced for hay diets in cold exposure, which increased the escape of dietary N from the abomasum and the efficiency of microbial synthesis. Cold exposure did not affect urea transfer from plasma to the rumen. Subsequently, two steers fitted with cannulas in the oesophagus and rumen were used in a 2x2 cross-over design to study the physical breakdown of different diets. Concomitantly, four steers, each fitted with a rumen cannula, were used in a 4x4 Latin square design to investigate removal of digesta components from the rumen. A combination of wet sieving and marker techniques for fluid, particulate and microbial movements was utilized. The fractional outflow rate (FOR) of 51Cr-EDTA in centrifuged rumen fluid was increased (P<0.05) from 1.78 to 2.10 per day by grinding of the hay diet, but was not influenced by the intake of an additional 257 g NaC1 per day. The FOR values of 103Ru-P in mixed rumen digesta and organic 35S in microorganisms were linearly correlated (P<0.05) and were not affected (P>0.05) by grinding and salt treatments