The value of artificially dried grass, silage made with added molasses and A.I.V. fodder in the diet of the dairy cow and their effect on the quality of the milk, with special reference to the value of the non-protein nitrogen

Abstract

An experiment has been carried out with dairy cows to measure the value of artificially dried grass, silage made with added molasses and A.I.V. fodder (silage made with mineral acid in quantity sufficient to bring the pH of the mass to between 3·0 and 4·0) in the diet, on the yield and quality of the milk. A preliminary period of 3 weeks when all cows were on the control diet was followed by an experimental period of 17 weeks. There were four treatments: a control ration consisting of hay, roots and concentrates; one in which artificially dried grass replaced part of the concentrates; a third in which molassed silage was fed; and a fourth including A.I.V. fodder. There were originally five blocks of four cows each, the four treatments being randomised in each block, each block of cows standing together in the cowshed to eliminate any possible effect of position. One block went dry after 8 weeks, but the remaining four blocks completed the experiment.

The losses of dry matter and digestible nutrients in low-temperature silage, with and without added molasses or mineral acids

“…Modern work has shown that the breakdown products of the "true" protein are of high nutritive value if the process has not proceeded too far, and this has been demonstrated by the authors (16). It is, therefore, more accurate to make allowance for this fact, and the corrected digestible "true" protein value is designed to meet the case.…”

“…process over ordinary or molassed silage is not so great as it is usually thought to be. The breakdown of "true" protein is reduced to a marked extent by the addition of acid, but so long as the decomposition has not proceeded too far, this, as has been pointed out (16), is no great disadvantage.…”

“…The digestible crude protein of silage is probably the best criterion of the value of the nitrogenous constituents. It has been suggested that the non-protein nitrogen compounds in silage are of equal value to the "true" protein, from which they were formed, so long as the breakdown has not proceeded beyond the stage of amino acids, and recent work at this Station (16) has confirmed this.…”

The chemical composition of grass silage

“…value is over 4-5. Below this level, the only change which occurs down to pH 2-5 is a reduction in the percentage of volatile bases from 9 to 4 per cent, a small change, negligible for most purposes. The somewhat greater formation of amino acids in molassed silage is of little import, since recent work at this Station (22) has shown that for milk production this fraction has a value which does not differ markedly from that of true protein.…”

A note on the analysis of covariance

“…These coefficients cannot, however, easily be separated from the treatment means, and for properly randomised experiments, in which the usual analysis is always a valid one, this modification would hardly ever be worth while. In a discussion (5) on this point in the design and analysis of dairy cow nutrition experiments, this conclusion was made provisionally, but has been substantiated by the actual results of an experiment conducted and analysed on the lines proposed (6).…”