Effect of Source and Level of Protein on Mineral Utilization by the Baby Pig

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Abstract
Four lots of 4 baby pigs each were assigned to dietary treatments of moderate (16%) or high (32%) protein from two different sources, casein or isolated soy. Feed intake was 20% less when high levels of either protein were fed. Growth was not affected by dietary treatment. Serum analyses showed that serum inorganic phosphorus was reduced and alkaline phosphatase correspondingly increased when high levels of soy protein were fed. Mineral balance studies showed that calcium and magnesium retention was greater when casein was the source of dietary protein. Increasing casein content of the diet enhanced the utilization of calcium, phosphorus and magnesium. Increasing the amount of isolated soy protein in the diet, however, was found to suppress the utilization of these elements. Optimum bone mineralization did not occur when soy protein was fed at the higher level. The lower level of isolated soy protein in the diet, however, allowed proper utilization of minerals for compact bone formation as did casein diets at either level of protein intake. This experiment indicates that as the amount of isolated soy protein in the diet increases, the availability of phosphorus, calcium and magnesium decreases if the total phosphorus content of the diet remains constant. It may be concluded that sufficient minerals are assimilated for optimum bone mineralization when isolated soy protein constitutes 20% of the diet, but not when it constitutes 40% of the diet.