Energy cost of eating in cattle given diets of different form

1. Energy costs of eating were determined from the increased rates of oxygen uptake by five steers aged 18 to 20 months and weighing 298 to 407 kg. 2. Five diets were tested: pelleted concentrate (500 g barley grain per kg, 400 g lucerne meal per kg, 90 g soya bean meal per kg, and 10 g NaCl, trace mineral and vitamin supplement per kg); pelleted lucerne; lucerne hay; chopped-grass hay (700 g brome per kg, 300 g fescue per kg); and chopped fresh turnips. The dry-matter concentration of the pellets and hays was approximately 900 g per kg while the turnips contained only 140 g per kg. 3. The rates of ingestion differed markedly between diets during the (15 to 50 min) twice-daily (morning and evening) feeding periods. On a dry-matter basis, the pellets were consumed most rapidly at a rate of 130 to 138 g per min, while the hays were consumed at approximately 38 g per min and the turnips at 30 g per min. 4. The energy costs per min spent eating were similar for all rations (27·6 to 35·6 J/ kg live weight). However, because of different rates of ingestion, the energy costs per kg DM ingested were different: 222 to 238 J/kg live weight for the pelleted foods, 1029 J/kg live weight for the hays and 1427 J/kg live weight for the turnips. 5. The energy cost of eating is more a function of time spent eating than a function of the amount of food ingested. Thus, rate of ingestion and duration of the meal are key factors in determining the energy cost of eating in cattle.