Levy, D., Agricultural Research Organization, Nve-Ya'ar Regional Experiment Station, PO, Haifa, Israel
Holzer, Z., Agricultural Research Organization, Nve-Ya'ar Regional Experiment Station, PO, Haifa, Israel
Ilan, D., Ministry of Agriculture, Extension Service, Israel

Four groups of 14 3-month-old Israeli Friesian male cattle were each given monensin supplement in their concentrates at the following rates: between 3 and 6 months of age, 0, 0, 25 and 35 p.p.m.; and between 6 months and slaughter, 0, 35, 35 and 35 p.p.m. They were offered hay at approximately 0·3 % of their live weight and concentrates ad libitum. Daily gain between 3 and 6 months was 1·36, 1·40, 1·50 and 1·57 kg/day, respectively; between 6 months and slaughter it was 1·22, 1·32, 1·33 and 1·24 kg/day, respectively. Differences in intake of concentrates were small. There were no significant differences in slaughter data. Daily carcass gain throughout the experiment was 0·71, 0·74, 0·77 and 0·76 kg/day, respectively. Monensin-supplemented animals were approximately 9% more efficient in the conversion of metabolizable energy into live weight or carcass weight than the control animals. Production of propionate in the rumen was significantly increased in response to monensin supplementation, and the acetate to propionate ratio was significantly reduced. © 1979, British Society of Animal Science. All rights reserved.