219. The nutritive value of proteins for milk production. V. The effect of high temperature and of season on the nutritive value of grass proteins, the supplementary effect of the maintenance ration on the production ration, and the effect of feeding a high-protein ration

Abstract

1. As regards the nutritive value of artificially dried spring grass, the protein appears to be unaffected by the temperature of drying even to the extent of scorching the grass. Early autumn dried grass has a biological value intermediate between spring and late autumn grass, while linseed cake has a very low value.2. The supplementary effect of the maintenance on the production ration has been shown when hay was substituted for straw in the maintenance ration together with a production protein intake of poor biological value.3. With an excess of protein in the ration most of the excess nitrogen was excreted in the urine, while both the milk yield and the biological value of the food protein fell considerably. It is possible that, together with an adequate amount of lysine in the protein ingested, a certain mixture of amino-acids is essential before maximum milk yield can be obtained.4. A study of the nitrogen metabolism shows that high-temperature drying has no effect, whereas marked effects were noted with the early autumn grass and more especially with the linseed cake. The hippuric acid nitrogen output decreased with the high-temperature dried grass, possibly the effect of a loss on drying of benzoic acid. With the high-protein diet an increased excretion of creatinine was noted with no alteration in the creatinine intake. The purin metabolism varies with the total nitrogen excretion, the allantoin increasing markedly in the high-protein period. This is due to an increased intake of purin base.5. The sulphur metabolism shows the results to be expected from previous publications except in the case of the high-temperature dried grass. It appears that the high-temperature treatment has in some way affected the nature of the sulphur compounds in the grass, with a consequent diminution in the retention.