Proportion Of Large Particles Research Articles

Large particle breakdown by cattle eating ryegrass and alfalfa.

The proportion of large particles (LP) broken down to small, insoluble particles by primary mastication (eating), rumination, digestion and detrition (rubbing) was determined for separated leaf and stem fractions of perennial ryegrass (Lolium perenne) and alfalfa (Medicago sativa) fed to cattle cannulated at the esophagus. Large particles were defined as those particles retained during wet sieving on a screen with an aperture of 1.18 mm. Reduction in weight of particles caused by solubilizing or digestion was not considered to be particle breakdown per se, and particles were corrected for this loss in weight. The proportion of LP in the forage broken down by primary mastication was 25 +/- 1.9% (means +/- SE). Breakdown of LP by rumination was calculated from the weight of total particles regurgitated and the proportion of LP in the regurgitated and swallowed remasticated material. The weight of LP regurgitated was corrected for the dry matter lost by digestion using lignin ratio in the LP entering the rumen and of the regurgitated digesta. Rumination accounted for 50 +/- 1.5% of LP breakdown. Fecal loss accounted for 8 +/- .8% of the LP in forage. Breakdown of LP by digestion and detrition was calculated as 17 +/- 1.3% from the difference between the LP eaten and those broken down by primary mastication, rumination and passing out in the feces. The significance of these results for predicting voluntary intake from laboratory analysis is considered.

Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of 100 µm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.

Laboratory Studies of Wet Milling

American malt milled commercially in a wet mill contained a higher proportion of large particles than commercially dry milled malt and occupied 30% more volume. Wet-milled kernels fragmented less t...

Studies of cattle and sheep eating leaf and stem fractions of grasses. 3. The retention time in the rumen of large feed particles

Pangola grass (Digitavia decumbens) and Rhodes grass (Chlovis gayana) cut as 6 and 12 week regrowths were separated into leaf and stem fractions and fed ad libitum to four cattle and eight sheep fitted with ruminal fistulae to determine the importance of particle size in controlling the retention time of feed in the rumeno-reticulum (rumen). Particle size was determined by using a wet sieving technique, and based on the cumulative dry matter distribution on the sieves of faeces from cattle and sheep; all particles >1.18 mm were described as large particles. The proportion of large particles was measured in the chopped diet offered, the masticated diet, the ruminal contents and the faeces. Chopped leaf and stem fractions contained 0.85 and 0.86 g/g large particles respectively. Mastication by cattle reduced the proportion of large particles in leaf and stem to 0.58 and 0.76 (P < 0.01), and mastication by sheep to 0.56 and 0.67 (P < 0.01). The proportion of large particles in the rumen of sheep was 0.236 and 0.249 for leaf and stem respectively (P > 0.05) and in cattle 0.272 and 0.345 (P < 0.05). The faeces contained relatively few large feed particles (< 0.045 for cattle and <0.018 for sheep). Cattle eating leaf and stem produced faeces containing 0.027 and 0.040 (g/g) large particles (P <0.05), compared with only 0,008 and 0.013 (P < 0.05) in sheep. Most of the large particles entering the rumen in the masticated feed disappeared in the rumen by breakdown to smaller particles or by digestion. In cattle the proportions that disappeared were 0.978 and 0.976 (P > 0.05) for leaf and stem, and in sheep 0.993 and 0.991 (P > 0.05). Large particles in leaf and stem were retained in the rumen of the sheep for 11.0 and 11.7 h (P > 0.05). Cattle retained large particles in all diets for a longer time (P < 0.01); 16.1 h for leaf and 20,2 h for stem (P > 0.05). Differences in retention time of large particles in the rumen did not appear to be the only factor controlling the retention of dry matter in the rumen and voluntary intake. A model was developed to describe the flow of large and small particles through the rumen. Intake simulation studies indicated that the most important factor influencing dry matter retention time in the rumen was the retention time of small particles (> 1.18 mm). Changes in the rate of breakdown of large particles had a small effect on dry matter retention time.

The voluntary intake, digestibility and retention time by cattle and sheep of stem and leaf fractions of a tropical legume (Lablab purpureus)

Hay made from the tropical forage legume Lablab purpureus was chopped and separated into leaf and stem fractions by using a gravity separator. Each diet was fed to four cattle and six sheep fitted with rumen fistulae to measure the digestibilities of the dry matter (DM), organic matter (OM) and neutral detergent fibre (NDF), and the retention times of DM, OM and NDF in the rumeno-reticulum (rumen) and the rumen volume. Mean voluntary intake of the DM in the leaf fraction was 79 % higher by cattle and 61 % higher by sheep than the stem fraction, and this appeared to be associated with the shorter time it was retained in the rumen. Both leaf and stem DM were digested to a similar extent by cattle. Sheep digested the leaf fraction to the same extent as cattle. However, the DM digestibility of the stem eaten by sheep was 0,061 lower than that of the leaf fraction (P < 0.05). Cattle retained the DM, OM and NDF in all diets for longer periods in the rumen than did sheep. This difference led to a 48% higher voluntary intake (g(kg body d-1) by sheep. The proportion of large particles that disappeared within the rumen was lower (P < 0.01) for cattle (0.968) than for sheep (0.994). The large particles of the leaf and stem fraction were retained for the same mean time by sheep (5.7 and 5.6 h), which was shorter (P < 0.01) than the corresponding times for cattle (13.8 and 21.6 h). The rate of disappearance of large particles in the rumen appeared to be only a minor factor causing the longer retention time of stem fractions in the rumen. The concentrations of volatile fatty acids and ammonia in the rumen were higher for leaf than stem fractions with no differences between cattle and sheep. The proportion of acetic acid for cattle (0.75) was higher (P < 0.05) than that for sheep (0.69) while the corresponding propionic acid proportions were lower (P < 0.01) in cattle (0.14) compared with sheep (0.19). These differences were associated with a higher passage rate constant for water flowing from the rumen and a higher digestion rate constant in sheep. It was concluded that both cattle and sheep ate more of the leaf than the stem fraction of the legume Lablab purpureus and that the higher intake of leaf was associated with the shorter time that it was retained in the rumen and was not due to differences in digestibility. Cattle had a smaller relative voluntary intake of legume than sheep, a difference that was associated with the longer time that digesta was retained in the rumen.

Nodal and paranodal membrane structure in complementary freeze-fracture replicas of amphibian peripheral nerves

Complementary freeze-fracture replicas of frog peripheral nerves have revealed new details of membrane structures at the node of Ranvier and paranodal axon-Schwann cell junction. At the node both E and P fracture faces of the axolemma have high particle concentrations (approximately 1350/sq. micron and 1600/sq. micron respectively) and these particles do not overlap when tracings from the respective fracture faces are superimposed. A high proportion of the E face particles are large (> 9.5 nm) and cast long shadows while the proportion of large particles in the P face is much lower. In the paranodal region the diagonal pattern of parallel rows in the junctional axolemma always has the same orientation within a given fracture face. In the E face, the parallel rows form a positive (+ 30 degrees) angle to the groove below and in the P face, a negative (-30 degrees) angle to the ridge above. This implies that the diagonal pattern derives from asymmetric subunits that are able to associate along only one axis and are unable to 'flip over' with respect to the junctional membranes.

Determination of the Masses of Charged Particles Observed in the Photographic Plate

A study has been made of scattering of 40 protons and 160 mesons in photographic emulsions in order to determine the mass of the individual particles. The spread in the values so obtained is large, but the evidence suggests that the majority of mesons recorded by the emulsion can be identified both with the mesons, of mass 200 me, commonly observed in cloud-chamber experiments and with counters, and with the μ-mesons observed in the photographic plates. The slow particles producing nuclear disintegrations, σ-mesons, appear to contain a large proportion of particles with a mass equal to that of the π-mesons.