Nitrogen metabolism of lactating ewes fed rumen-protected methionine and lysine.

Twenty multiparous, crossbred, black-faced ewes and their newborn twin lambs were assigned to one of four dietary treatments in a 2 x 2 factorial experiment to examine the effects of increased supply of CP or a mixture of encapsulated methionine and lysine or both on the performance of ewes and their nursing twin lambs. Ewes were fed ad libitum amounts of either a 10.2% low CP diet or a 16.2% moderate CP diet with or without additional encapsulated amino acids. Nitrogen metabolism trials were conducted simultaneously on both ewes and lambs at wk 2, 4, and 8 of lactation. Analyses were conducted for blood urea N, plasma 3-hydroxybutyrate, lactate, NEFA, insulin, and amino acids (plasma, feed, and milk). Ewe DMI, BW, BW gain, and milk yield were not changed by dietary treatments. Balance of N and N digested were increased by moderate CP treatment. The portion of retained N used for milk synthesis was increased by low CP treatment. Methionine and total branched-chain amino acids were increased by encapsulated amino acids and by protein treatment. Gains in BW and N balance were increased in lambs nursing ewes fed protected amino acids. Increased growth of nursing lambs would be an important beneficial effect of supplementing diets of ewes with encapsulated methionine and lysine.