Relation of Dietary Protein Levels to Reproduction in the Rat

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Abstract
The relation of dietary protein levels to reproduction has been studied in adult rats placed the day of breeding on purified diets supplemented with all known dietary essentials and containing casein as the source of protein. Under these conditions the 5% protein (6% casein) level was apparently the critical level, as above this level reproductive performance was normal but below it reproduction was severely disturbed. Pregnancy on the protein-free and low protein (2.5%) diets was characterized by a high incidence (70 to 100%) and early occurrence of resorptions. The resorptive process was rapid and implantation sites were often not detectable at the end of gestation. Marked decreases in maternal body weight also occurred. With the exception of loss of maternal body weight, the general picture is similar to that observed for pregnancy in the B6-deficient rat and in the hypophysectomized rat, and suggests the possibility of hormonal deficiencies in these animals. The critical need for protein during the earliest stages of placental and fetal development is in contrast with the reproductive success which resulted when a protein deficiency was instituted only shortly after implantation. The normality of pair-fed controls when the protein level was raised to 30% eliminated the factors of food restriction and of other dietary deficiencies as causes for these reproductive disturbances. No young with macroscopic congenital abnormalities were observed in any group on the protein-free diet.

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