[Experimental studies on the ketogenic effect of high doses of proteins in dairy cows]. / Experimentelle Untersuchungen zur ketogenen Wirkung hoher Eiweissgaben bei Milchkühen

A 14-month feeding experiment was conducted with 16 high-yielding cows, each given a daily supplement of 2 kg soya meal regardless of milk yield or the stage of lactation, in comparison with 8 normally-fed cows. At monthly intervals various parameters of carbohydrate, fat and protein metabolism and of liver function were determined. At the end of the trial, samples of liver were obtained by biopsy for morphological and histochemical examination. Supplementation had a pronounced effect on milk yield and fat content, averaging over 900 kg of milk and 0.2% fat content more than during the preceding year. The parameters of metabolism revealed clear signs of subclinical ketosis, particularly during the first third of the trial period. Changes were greatest during the 3rd and 4th months of the trial, when the protein content of the ration was particularly high (over 3 kg) and when the energy supply ratio was particularly unfavourable (PEQ 300). At the end of the trial some abnormalities were detected in individual animals in the biochemical properties of blood and urine, and the morphological, histochemical and ultrastructural appearance of the liver. These changes included increases in KK, BTS and bilirubin concentrations in the blood; ketonuria, proteinuria; perilobular fat infiltration with glycogen depletion; changes in succinate dehydrogenase and acid phosphatase activities. In most animals the liver seemed to have become adapted to a high protein intake.