A previous experiment (Sutton, Abdalla, Phipps, Cammell and Humphries, 1995) showed that low digestibility is a major cause of the poor utilisation of urea-treated whole crop wheat (WCW) by lactating cows. The purpose of the present experiment was to examine energy balance in more detail by means of indirect calorimetry.

Four multiparous Holstein-Friesian cows were offered diets based on spring wheat (cv Axona), harvested on 11 August at 603 g dry matter (DM)/kg and preserved with 20 or 40 g urea/kgDM (WCW-20, WCW-40), and first-cut perennial ryegrass silage (GS). For GS, WCW-20 and WCW-40 respectively, DM was 213, 801 and 712 g/kg; crude protein (CP) 124, 163 and 171 g/kg DM; ammonia-N 3.1, 4.6 and 7.6 g/kg DM; pH 3.9, 6.7 and 7.2. The cows were offered four diets in a 4 X 4 latin square with 4-week periods starting 10 weeks after calving. In week 4 of each period urine and faeces were collected for 6 days and gas exchange was measured for 3 days in respiration chambers.