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What Is the Best System of Measuring the Nutritive Energy of Farm Feeds in Practice?

U. S. Department of Agriculture

Abstract

In order to determine whether net energy, total digestible nutrients, or metabolizable energy is the best system for measuring the nutritive energy of farm feeds in practice, two sets of dry cows were fed on two different rations in such quantities that they remained at approximately uniform body weight. The average daily quantities of net energy, total digestible nutrients, and metabolizable energy consumed per cow in each of the two groups were then calculated and compared in such a way that it can be seen which of the three systems of units shows most accurately the relative values of the two rations for maintaining uniform body weight.

The rations used were, in the one case, alfalfa hay; and, in the other, timothy hay and old-process linseed meal combined in the proportions of ten parts of hay to six of meal. The feeds were analyzed by the Bureau of Chemistry. In Table 1 the results obtained are compared with the average figures given for the same feeds by Henry and Morrison. In the two other tables the figures for net energy, total digestible nutrients, and metabolizable energy were calculated from the analyses of the Bureau of Chemistry.

In Table 2 are given some results for the individual cows. The figures for net energy consumption in this table and all the figures given in Table 3 are calculated to a basis of 1,000 pounds body weight according to the two-thirds power of the weight.

Animals which are to be used in body-weight experiments to determine the nutritive energy of foods, should be mature and farrow. It will be seen from Table 2 that the animals used in this experiment were well past the stage of rapid growth, but they were not all quite mature. The immature animals were fairly evenly distributed between the two groups. All the animals used were supposed to be farrow when put on the experiment, but it turned out that one, No. 99, was about three months pregnant after the experiment had been running about ten weeks. She was, therefore, taken off the experiment after it had been running for three months.

The average results calculated in three different ways are shown in Table 3¹. In one case the results are calculated with cow 99 alone omitted. This is not considered very satisfactory, as it leaves an animal under four years old, No. 453, in the timothy and meal group with no similarly young animal to balance her in the alfalfa group. The results have, therefore, also been calculated with cows 99 and 453 both omitted, and again with all cows included. However they are calculated, they indicate that total digestible nutrients furnish a somewhat better system for calculating the nutritive energy of feeds in practice than do net energy values, and that metabolizable energy is much the best of the three systems.

It is intended to continue the experiment for some months as at present, and then to reverse the rations of the two groups of cows and continue for several months longer with the rations reversed.