121 pH and ammonia nitrogen (NH 3 -N) were similar among the treatments. Plasma urea nitrogen (PUN) in treatments II and III were significantly (P<0.05) less than the control (14.87 and 18.60 vs. 25.15 mg/dl, SE = 1.637) (P<0.05). Concentrate restriction and its substitution by liquid whey in feeding of Holstein steers A.R Bayat, R. Valizadeh and A.A. Naserian Department of Animal Science, College of Agriculture, Ferdowsi University P.O. Box: 91775-1163, Mashhad, Iran Email: arbayat2001@yahoo.com Introduction A large quantity of whey is produced in Iran and mostly is discharged into streams and seasonal rivers, which cause environmental pollution. Whey as a nutritious dairy by-product can effectively be fed to ruminants (Bayat et al. 2002). This experiment was conducted to study the effects of concentrate substitution by liquid whey on performance, rumen and blood parameters of the Holstein steers. Materials and Methods Twelve Holstein steers with average body weight of 150 kg (s.d. 27) were selected and stratified based on weight into 3 groups and randomly assigned to the treatments. Experimental design was Completely Randomized Design with three treatments and four replications. Lucerne hay was fed at the level of 0.7 percent (DM Basis) of body weight. Liquid whey was given ad lib. No drinking water was provided. Experimental treatments were: І. Normal concentrate feeding (ad lib) as control, II. Concentrate restricted at the level of two third of concentrate intake of the control, III. Concentrate restricted at the level of one third of concentrate intake of the control. The experimental period was 100 days including 15 days adaptation and 85 days sample collection period. Lucerne hay and concentrate were fed separately. Diet was formulated based on NRC (1989) recommendations for 3-6 month growing calves. Blood samples from jugular vein were taken 3h after morning feeding and immediately centrifuged (3000 rpm and 10 minutes) to obtain their plasma. Rumen liquor samples were taken 3h after morning feeding by stomach tube and evacuation pump. Analyses of feed and feces were conducted based on AOAC (1984). Analyses of NDF and ADF were conducted based of Van Soest method (Georging and Van Soest 1970). Acid insoluble ash (AIA) was used as internal marker for apparent digestibility determination (Van Keulen and Young 1977). Data were analyzed by SAS software (1996). Results Whey consumption of treatment III increased by 12.68 percent in comparison to treatments I and II (Table1). The steers in treatments I, II and III obtained 41.2, 49.3 and 55.7 percent of their daily dry matter intake (DMI) from whey respectively. There was a significant difference among total DMI. The lowest and highest intakes were observed in treatments III and I respectively. Lucerne intake in treatment III was higher than treatments I and II (P<0.05). Table 1 Feed intakes of the steers (kg/d) Table 2 Nutrient apparent digestibilities (g/g) Among the nutrient apparent digestibilities (Table 2) only apparent digestibility of ADF in treatment III was significantly increased in comparison to the control (P<0.05). Average daily weight gain (ADG) and feed conversion ratio (FCR) are shown in Table 3. Increasing concentrate restriction leads to linear decrease in ADG although it was not significant. There was no significant difference among feed conversion ratios obtained in this study. Rumen and blood Table 3 Average daily gain and feed conversion ratio. Treatment I II III SE ADG (kg/d) 1.415 1.247 1.103 0.096 FCR (kg/kg) 4.56 4.42 5.26 0.410 Conclusions It can be concluded from the results of this experiment that substitution of concentrate by liquid whey in an appropriate ratio could be efficient and economical feeding strategy in the area. Although this conclusion is highly attributed to the market price of feed ingredients. References AOAC. 1984. Official Methods of Analyses. Association of official analytic chemists, Washington, DC. Bayat, A.R. Valizadeh, R. and Naserian A.A. 2002. Replacement of water by whey and its influence on performance of Holstein steers. Proceedings of BSAS. UK. Georging, H. K. and Van Soest, P.J. 1970. Forage fiber analyses (Apparatus, Reagents, Procedures and some Applications). Agric. Handbook No. 379. USDA-ARS, Washington, DC. National Research Council. 1989. Nutrient requirements of dairy cattle. National academy press. Washington, DC. Van Keulenl, J. and B.A. Young. 1977. Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. Journal of Animal Science: 44: 282. Treatment I II III SEM DM 0.76 0.82 0.87 0.034 OM 0.77 0.83 0.88 0.032 CP 0.80 0.85 0.91 0.030 CF 0.34 0.52 0.63 0.090 NDF 0.41 0.58 0.64 0.086 ADF 0.24 0.49 0.64 0.082 Treatment I II III SEM Whey As Fed 48.4 8 48.5 0 54.64 4.125 DM 2.63 2.63 2.96 0.224 Lucerne (DM) 1.11 1.22 1.45 0.067 Concentrate(DM) 2.64 1.58 0.90 0.139 Total DMI 6.38 5.43 5.31 0.118