UTILIZATION BY DOGS OF THE NITROGEN OF HEATED CASEIN

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Abstract
Young dogs were fed from weaning to maturity on purified diets containing casein, unheated or heated at 140 C or 200 C for 15 or 30 min. The growth of the animals on the heated protein was inferior, particularly on that exposed to the higher temp. Little advantage was seen in the use of 24% as compared with 18% heated diet and rapid deterioration occurred in one dog when 36% heated casein was substituted for the 18% diet. The admn. of 40 g. of l-lysine dihydrochloride in 52 days to one dog caused slight but perceptible improvement in growth and serum protein level. A similar change occurred in another dog on the heated diet when 3 g. lactalbumin was given daily for 2 months. The total serum protein and albumin levels, but not the globulin level, were progressively lowered in all the animals on the heated protein. Hemoglobin concn. was also decreased although less strikingly. Total N intake was maintained equal in the paired animals on heated and unheated diets by force feeding. Nevertheless decreasing retention and eventual N loss occurred on the heated protein, with most of the excess excretion appearing in the feces. The apparent digestibility of the casein heated at 200 C was 28, of that heated at 140 C, 67, and of the unheated 91. True digestibility of the more severely heated casein in one case was found to be 30. Yellow livers, apparently fatty, were found in all the dogs fed the 200 C heated casein, and low heart and muscle creatine in one. These conditions point to possible methionine deficiency. The differences between these observations and those seen previously in rats similarly fed indicate poorer capacity on the part of the dog for absorption of any abnormal amino acid or peptide forms present in the heated casein but similar net loss of biologic value in the 2 species.

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