The standard method of measuring the digestibility of pasturage involves the daily cutting of fresh herbage from the field for feeding to the experimental animals (1, 2). That the herbage cut may not be representative of that consumed by animals actually grazing has been noted (1, 3, 4), but such feeding trials are likely to be valuable in connexion with work on the relation between composition of faeces and feed intake, and in studying the factors affecting digestibility. However, the method suffers from several disadvantages. Firstly, the labour involved in the daily cutting and sampling of the feeds is considerable, and various errors in sampling are introduced. Secondly, during the ten to fourteen days of the feeding trial, the grass available on the field will increase in maturity, and so will be likely to decrease in digestibility. ' Table 1 gives data from two such feeding experiments conducted during 1947. The crude protein contents of the herbage consumed by the sheep in cages during the successive four-day sub-periods of each experiment are given, and below these is recorded the digestibility of the dry matter eaten during the sub-period (these figures, over such short periods, can only be approximate). Trial Trial 1 2 % CP. % D.M % CP. % D.M eaten dig. eaten dig. Period 1 15.4 73.0 14.65 71.0 Period 2 13.15 68.4 12.95 64.5 Period 3 11.35 60.9 11.2 64.7 TABLE 1. Digestibility data for grass (average of three sheep).It is seen that as both trials progressed, the protein content of the herbage eaten by the caged sheep decreased, this being accompanied by a decrease in the dry matter digestibility of the grass. By taking aliquot samples of each day's feed, and bulking for chemical analysis, an average figure is obtained, but variation in feed quality is obviously undesirable in accurate experiments. This has been considered by Forbes and Garrigus (5) who reduced the feeding period with steers to six days in order to minimise errors due to the changing herbage composition. In the experiments of Sheehy (6) separate plots on a uniform sward were mown on 14 consecutive days, and then after 35 days growth the plots were mown in the same order throu.ghout a further 14 days, and the herbage fed to caged sheep. This method gave herbage of constant composition, but involves conditions of management which are rather artificial.Forbes and Garrigus (5) have also considered the difficulty of feeding the same weight of dry matter to the animals each day. This they overcame by carrying out a rapid moisture determination on the cut herbage each day before weighing the feeds.Ul
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