This work was conducted at Ras Sudr Research Station, which locates in South Sinai Governorate, belonging to Desert Research Center, to investigate the effect of short- term feeding (90 days) Barki lambs on Kochia indica shrubs as forage (treated group, T) compared with clover hay (control group, C). The physiological responses were body fluids distribution, water balance, some plasma electrolyte concentrations (Sodium, Na⁺ and Potassium, K⁺), in-vivo body composition and growth performance during summer. The results revealed that, live body weight (LBW) changes over the experimental period were generally positive in both T and C groups without significant difference. The rates of LBW change in the two experimental groups represented +32.79 and +32.97%, respectively. Regarding the effect of period on body fluids distribution, the rates of changes in total body water (TBW), extracellular fluids (ECF), intracellular fluids (ICF) and interstitial fluids  (ISF) were highly significant (P<0.01) in the two groups with values being +36.27, +24.68, +43.37 and +18.33% vs. +36.27, +33.25, +38.47 and +32.43% respectively for T and C groups. The averages of daily-retained water were 44.6 and 46.6 g/head for T and C groups with respective ratios of daily gain in live body weight of 65.8 and 68.7%.  Plasma electrolytes showed that lambs fed Kochia indica elevated plasma Na⁺ concentration (P<0.01), while control group kept their plasma Na⁺ concentration approximately constant. Plasma K⁺ concentration increased significantly for both groups, with higher increase in lambs fed Kochia indica (+26.38%) than lambs fed clover hay (+2.71%).  By the end of experimental period, the mean values of plasma, blood and red cells volumes increased in both groups, this increase was more for lambs fed Kochia indica than those fed clover hay.  For the Antipyrine dilution technique, the prediction equations showed no variations in body composition and growth performance between treated and control groups. Also results showed no significant effect for Kochia indica on in-vivo body composition fractions since total body protein (TBP), total body fat (TBF) and total body ash (TBA) increased throughout the experimental period (P<0.01) without significant differences between treated and control groups.  The averages of daily body weight gain throughout the study period were the same values of 67.8 g/h/d in the two groups.     Water balance indicated that lambs fed Kochia indica showed higher water turnover rate i.e total water