Influence of some digestive processes on the digestion by cattle of cereal grain fed whole

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Abstract
Pen studies were conducted with cattle in which the digestibility, rate of fermentation, site of digestion and grain loss in faeces were measured in diets comprising 4.8 kg of one or other of four cereal grains together with 2.4 kg of pasture hay. The cereals were Avon oats, Swan oats, Olympic wheat and Emblem wheat with natural weights of 48.3, 60.5, 81.3 and 78.8 kg hl-1 and particle size index 24, 35, 31 and 14, respectively. The apparent in vivo digestibility of Avon and Swan oats of 71.9 and 74.6 did not differ significantly (P > 0.05). However, there was significantly less grain cracked during initial mastication (12.5 vs. 19.2 per cent and a lower percentage of grain voided in faeces (4.3 vs. 9.3) for Avon compared with Swan oats (P < 0.05). The in vivo digestibility of wheat grain was significantly higher for Olympic than for Emblem (77.5 vs. 72.6 per cent) ;these performances were accompanied by lower percentages of grain cracked during initial mastication (17.0 vs. 22.3) and less whole grain DM voided in faeces (14.6 vs. 18.4 per cent) for Olympic compared with Emblem (P < 0.05). The major difference in the digestion of oat and wheat varieties was that rumination accounted for a high proportion of the breakdown of oat grain whereas the wheat varieties were digested by rumen fermentation with only a small proportion of grains broken down by rumination. The breakdown of whole grain in rumination was important for all rations. For the light oats, heavy oats, soft wheat and hard wheat, rumination accounted for 66 per cent, 44 per cent, 27 per cent and 17 per cent of the total breakdown respectively.