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The effect of dietary fat level on calcium utilization by the chick Salmon, Raymond Edward

Abstract

A series of three balance experiments were conducted to study the effect of the addition of animal fat to the diet on the utilization of calcium by growing chicks. In two experiments, the chicks were fed diets containing four levels of calcium, 0.75%, 1.0%, 1.25% and 1.50%, with a calcium: phosphorus ratio of 1.7:1. A fifth treatment was fed in which the top calcium level was adjusted to provide a calcium:phosphorus ratio of 2.5:1. All diets fed contained an excess of Vitamin D. Each of the five mineral treatments was fed as a control diet, to which no supplemental fat was added, and as a high fat diet, in which 8% of ground cellulose was replaced by 8% animal fat. In one experiment the diets contained 24% protein. In the other, the protein level was reduced to 20.6%. In the third experiment, to clarify the effect of adjusting the calcium:phosphorus ratio in the diet, three levels of calcium were fed with calcium:phosphorus ratios of approximately 1.5:1 and 2:1. As in the previous experiments, the different mineral levels were fed as low fat diets, and as high fat diets containing 8% animal fat. The diets fed in this experiment contained 23.6% protein. Criteria of calcium utilization used in all these experiments were rate of growth, feed efficiency, calcium balance (% of calcium retained) and calcium retention (calcium retained per 100 grams of gain in body weight). In addition, in the first two experiments, the percentage of bone ash was determined on a sample of chicks from each group at the conclusion of the experiment. It was found that: 1. The calcium requirement for growth and feed efficiency was not affected by the addition of 8% animal fat to the diet. The calcium requirement for maximum growth when the diet contained 24% protein appeared to be between 1.0 and 1.25% of the diet. All levels of calcium fed provided equal growth with diets containing 20.7% protein. 2. The addition of 8% fat to the diet significantly impaired bone calcification when the diet contained 24% protein. No impairment was evident at the 20.7% protein level. Diets containing 1% calcium provided calcification equal to that provided by diets containing 1.25% or 1.5% calcium. 3. Calcium balance (% of calcium retained) was found to be influenced excessively by differences in feed efficiency. A more useful index of calcium utilization was calcium retention, expressed in terms of body weight. 4. The addition of 8% animal fat to the diet impaired calcium retention (expressed as calcium retained per unit gain in weight) when the diet contained 1% to 1.5% calcium. In the case of the low fat diets, calcium retention rose as the level of calcium in the diet was increased to 1.25%, and remained constant as the calcium level was increased further to 1.5%. When fat was added to the diet, calcium retention rose more slowly as the calcium level was increased, and failed to reach the maximum retention of the low fat diets. The degree to which calcium retention was reduced was not sufficient to affect growth, in the presence of vitamin D above the usual allowance. 5. The addition of 8% animal fat to diets containing 24% protein increased the rate of growth and improved feed efficiency. The addition of fat to diets containing 20.7% protein did not affect the rate of growth and had little, if any, effect on feed efficiency. 6. Adjusting the calcium:phosphorus ratio of the diet within the limits tested did not affect growth, calcification, or calcium retention.

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