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Dietary Protein Quality, Protein Quantity and Food Intake: Effects on Lactation and on Protein Synthesis and Tissue composition in Mammary Tissue and Liver in Rats^1,2,

Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523

Rate of protein synthesis in mammary tissue and liver as well as pup weight and milk yield were measured at d 15 of lactation in rats fed throughout gestation and lactation diets that varied in protein quality (wheat, wheat supplemented with lysine and threonine or casein supplemented with methionine), protein quantity [11 or 21% (wt/wt)] and feeding level (ad libitum or pair-fed to 100 or 85% of the consumption of dams fed wheat ad libitum). Improvement in dietary protein quality or quantity at the ad libitum feeding level produced large increases in mammary protein synthesis and pup weight; pair-feeding at 100 or 85% of the ad libitum wheat consumption level reduced or eliminated these increases. Increases in protein synthesis and pup weight associated with protein quality improvement were of similar magnitude to those associated with nearly doubling protein content of maternal diets. The responses of liver protein synthesis to dietary manipulation were qualitatively similar to those seen in mammary tissue. These data demonstrate that maternal dietary protein quality, protein quantity and feeding level all affect mammary protein synthesis and pup weight, and that, considered across all diets, changes in mammary protein synthesis are highly correlated with changes in pup weight and protein nutritional value.

KEY WORDS: • protein synthesis • mammary tissue • lactation • dietary protein quality and quantity • liver

¹ Supported by U.S. Department of Agriculture (USDA) Competitive Grants Programs in Human Nutrition, Grant no. 59-2081-1-1-648-0.

² Preliminary report presented at the annual meeting of the Federation of American Societies for Experimental Biology, 3 April 1984, St. Louis, MO. Sampson, D. A., Hunsaker, H. & Jansen, G. R. (1984) Mammary protein synthesis in lactating rats fed diets varying in protein quality, quantity and feeding level. Fed. Proc. 43, 668 (abs. #2243).

³ Current address: USDA/ARS (Agricultural Research Service), Western Human Nutrition Research Center, P.O. Box 29997, Presidio of San Francisco, CA 94129.

Manuscript received 19 February 1985. Revision accepted 20 November 1985.