Forty eight crossbred ewes at the last two months of pregnancy were divided into two similar groups (24 in each). Ewes in the first group were fed untreated concentrate feed mixture (UPP), while in the second group were fed concentrate feed mixture treated with formaldehyde (1% of CP) (PP). Wheat straw was offered ad lib for the two groups. Born lambs from both the two groups suckled their dams until weaning at 12 weeks of age. Results obtained showed that the digestibility coefficients of all nutrients and nutritive values and the intake of DM, TDN and DCP by ewes were significantly higher (P<0.05) for PP than UPP ration. The yield of colostrums and milk and their contents of fat, protein, SNF and TS and the concentrations of immunoglobulin fractions (IgG, IgM and IgA) in colostrum were significantly higher (P<0.05) for PP than UPP. Moreover, milk yield for both groups increased with advancing lactation period up to 8 weeks and decreased afterwards, while the contents of all milk constituents showed opposite trend. The number of weaned lambs per ewe was significantly higher (P<0.05) and the mortality rate was significantly lower (P<0.05) for PP than UPP, but it was nearly similar for male and female lambs. The birth and weaning weight, total and daily weight gain of lambs as well as total birth and weaned weight and weight gain of lambs per ewe were significantly higher (P<0.05) for PP compared with UPP as well as for male than female. Net revenue of lambs was significantly higher (P<0.05) for PP than UPP and for male than female. The count of red and white blood cells and the concentrations of total protein, albumin, globulin, IgG, IgM and IgA in plasma were significantly higher (P<0.05) for PP compared with UPP and increased significantly (P<0.05) with the progresses of suckling period, but nearly similar for male and female. The incidence of diarrhea, respiratory, septicemia, navel and general weakness were significantly lower (P<0.05) for PP than UPP, decreased markedly with the progresses of suckling period and nearly similar for male and female lambs.