The object of this communication is to give an account of an experiment, carried through in the autumn and winter season of 1934–5, designed to determine the changes in composition involved in making silage by the ordinary, molasses and A.I.V. processes. The changes in composition included those of both crude as well as digestible nutrients.

1. Waksman's simplified scheme of fractionation was used in attempts to trace the organic transformations occurring in some tropical samples of composts, soils and peats.

2. It was found that a useful partition of the nitrogenous substances into hydrolysable and resistant fractions could be effected by boiling with 5 per cent sulphuric acid for 6 hours.

3. Two profile layers of a black calcareous Trinidadian clay soil were compared with two horizons of a prairie soil examined by Waksman & Stevens. The surface layers of both soils were found to be similar in chemical characters, but the lower subsoil layers of the Trinidadian soil gave evidence of a more advanced and profound degree of organic decomposition.

4. Serial soil samples, taken from eight undisturbed natural profiles representative of humid tropical soil types occurring in Jamaica and Trinidad, were similarly examined.

The term “guano” is applied almost wholly to the excrement of sea-birds and, since it contains a high proportion of nitrogen and phosphorus, guano forms a very valuable fertilizing material. The Union of South Africa has a large number of small islands scattered round the coast which are used as breeding grounds by various sea-birds. The deposits of guano from different islands vary considerably and are therefore systematically mixed to obtain an approximately uniform grade of material. The average analytical results for the years 1921–8 were: 10·0 per cent nitrogen, 11·2 per cent phosphoric oxide, 2·0 per cent potash.

Some time ago, the author (Hendricks, 1935a) pointed out a modification which may occasionally be desirable in the application of co-variance analysis to experimental data. It was suggested that, in some instances, it is more logical to base the analysis on the assumption that the slope of the line of regression varies from class to class than on the assumption that the regression coefficient has the same value for each class of observations.

Feeding trials with sheep, subsisting out-of-doors on typical winter rations of known dry-matter and starch-equivalent content, have been carried out during the winters of 1933–4, 1934–5 and 1935–6. Records have been kept over these periods of the live-weights of the animals and their daily consumption of dry matter and starch equivalent.

It has been found that the standards of appetite, in terms of lb. dry matter, proposed by Prof. T. B. Wood are uniformly too high, a result in harmony with the findings of Prof. J. A. S. Watson and co-workers at Oxford. It is suggested that Prof. Wood's values should be multiplied throughout by the factor 0·85 in order to obtain reasonable measures of the appetites of sheep at different live-weights.

The data from the feeding trials have been used in an attempt to decide between the old and the recently proposed standards for the maintenance starch-equivalent requirement of the 100 lb. sheep, namely, 0·74 and 1·26 lb. of starch equivalent per day. The results point to the reliability of the higher figure, and it is shown that the results of recent work on the energy metabolism of sheep are in harmony with this conclusion.

A table embodying a revision of Prof. Wood's feeding standards for sheep is included in the paper.

A technique for measuring the appetites of sheep on pasture is described.

Results are given to show that sheep consume a bigger ration, in terms of lb. dry matter, when on pasture than when subsisting out-of-doors on the winter type of diet composed of hay, swedes (or kale) and concentrates. This difference was noted even on grass that had deteriorated in quality, in one case as a result of hot, dry weather in early summer, and in a second case as a consequence of cold, dry weather in spring. With young, leafy pasturage at its best, however, the distinction is most marked.

In the March of 1934, to quote but one example, four pure-bred Suffolk wethers, of live-weight varying from 120 to 181 lb., were shown to consume, on a diet of concentrates (350 g. daily), swedes (ad lib.) and chaffed hay (ad lib.), only 80–88 per cent of the amounts of dry matter predicted on the basis of Wood's feeding standards. During the following May, when grazing leafy pasturage of very good quality (digestion coefficient of organic matter = 81·l per cent), the appetites of the same sheep (range of live-weight now from 137 to 201 lb.) were found to have undergone a striking stimulation, the mean daily consumption of dry matter now being from 104 to 117 per cent of the amounts predicted from the standards. This implied that the sheep were consuming 1·13, 1·37, 1·13 and T53 lb. respectively more dry matter per day than they would have eaten had the diet consisted of hay, concentrates and swedes. The increased appetite is to be attributed to the superior palatability of the young grass.

Experiments have been carried out from 1930 to 1935, to investigate the composition, digestibility and yield of meadow hay cut at a normal time, and also of hay cut some 3–5 weeks earlier. Due consideration has been given to the “aftermath” growth occurring on the areas cut for the early hay between the times of cutting of the early and ordinary hay.

As was expected, the early hay, being less mature, was of better composition and digestibility than the ordinary hay. The average crude protein contents were 12·2 and 7·9 per cent of the dry matter respectively.

The yield data, average of 5 years, are summarized below, stated as lb. per acre, the early hay values including the aftermath yields.

1. The solubility of the phosphorus of soils and of other phosphatic materials in solutions of sodium hydroxide has been investigated. A method for the extraction and determination of the soluble phosphorus is described.

2. With acid soils, especially when the exchangeable calcium has been removed by leaching, an approximately constant amount of phosphorus is extracted by sodium hydroxide solution of strengths from 2 per cent to 20 per cent. The soda-soluble fraction amounts to 90 per cent of the total phosphorus.

3. Soils containing free calcium carbonate vary in the solubility of their phosphorus in sodium hydroxide solutions. Some behave similarly to acid soils, whilst others show only a small fraction of their total phosphorus to be soda-soluble. The extraction is complicated by the presence of calcium carbonate, which can precipitate from solution compounds which, in its absence, are soda-soluble.

Although silage Has Been Made in this country for more than 50 years, the exact nature of the chemical and bacterial changes which occur during the period of ripening is still very imperfectly understood. There are several reasons for this.

(1) The chemical changes are compounded of those due to plant respiration and those brought about by bacterial growth, and since these take place to a large extent simultaneously, it is difficult to apportion the amount of the total change to each factor separately.

(2) There is good reason to believe that the extent and rapidity of the changes which occur in the body of the silo are influenced by such variable factors as the external temperature, the moisture content, botanical species and age of the crop, and the season of the year when cut.

(3) They are also dependent upon the method of packing at the time of ensiling, since this ensures more or less anaerobic conditions, and will therefore affect both the nature of the plant respiratory changes and the kind of bacterial flora which develops.

The investigations previously described (1) have demonstrated that the changes occurring in the early stages of silage fermentation result in simultaneous development of acidity and degradation of proteins. There seems little reason to doubt that the lactobacilli play an effective part in the former by virtue of their formation of lactic acid. Contributions to proteolysis are undoubtedly made by various groups of bacteria, and in the later stages of ripening the spore-forming anaerobes, if numerous, will cause extensive protein breakdown and formation of volatile acids, especially butyric acid. The growth of the latter group of bacteria is greatly affected by the pH of the silage, for at values below about 4·0 the only group capable of anything like active multiplication is the lactobacilli. In fact the A.I.V. method of making silage consists in the addition of mineral acids at the commencement in quantities sufficient to reduce the pH to approximately 3·5. The production of good silage with a minimum loss of feeding value, low proteolysis and the presence of only small quantities of butyric acid may therefore be regarded as depending on the formation of sufficient acid in the earlier stages to retard the activities of the obligate anaerobes and proteolytic bacteria in the later stages.

Over a 12-day fattening period the use of maize in the poultry-fattening ration has no detrimental effect on the consistency of the body fat.

When fattening is rapid and live-weight gains are satisfactory, the type of fat deposited in the bird is harder than that laid down on a normal ration containing mixed cereals and a protein supplement.