Holzer, Z., Agricultural Research Organization, Institute of Animal Science, Nve Ya'ar Experiment Station, PO Haifa, Israel
Levy, D., Agricultural Research Organization, Institute of Animal Science, Nve Ya'ar Experiment Station, PO Haifa, Israel
Folman, Y., Agricultural Research Organization, Institute of Animal Science, Nve Ya'ar Experiment Station, PO Haifa, Israel

The fattening process of male cattle was divided into three weight stages: 150 to 250kg, 250 to 400kg, 400 to 490kg. Seventy animals were fed either a control (C) diet containing 10·3 MJ/kg metabolizable energy and some hay, or an experimental (E) diet containing 8 4 MJ/kg, in which NaOH-treated wheat straw (450g/kg) and long straw (50 g/kg) were incorporated. The diets were given during the three weight stages to five treatment groups as follows: 1. C-C-C. 2. E-E-E. 3. C-E-E, 4. C-E-C, and 5. E-E-C. The average daily gain and metabolizable energy conversion ratios were: 1344, 980, 1127, 1145, 1094g/day and 71·4, 90·6, 77·3, 73·7, 79·8 MJ/kg live weight, respectively. The saving of concentrates plus hay in groups 2 to 5 compared with group 1 was 1·33, 1·65, 0·84 and 0·91 kg/kg live weight respectively, and the concentrates plus hay by straw replacement ratio was 3·80, 2·12, 2·00 and 3·06, respectively. Dressing percentage and percentage of fat in the large depots of the animals in groups 1 to 5 were 57·2, 58·7, 58·3, 57·8, 57·9 and 3·88, 2·28, 2·52, 3·42, 2·81, respectively. The results suggest that it is not economical to feed the E-diet to animals before they reach a weight of 250 kg, and that termination of the feeding process by a highly concentrated diet is not advantageous. © 1980, British Society of Animal Science. All rights reserved.