Estimation of feed and energy intake of grazing cattle using faecal nitrogen and n-alkane method

Feed and energy intake of cattle grazed on low input grassland were investigated by experiments in 1996 and 1997. The investigations were carried out by using the n-alkane dotriacontane (C-32) as external marker according to Mayes et al. (1986) in combination with faecal nitrogen as internal marker according to Schmidt et al.(1999a). Galloway and Charolais steers were used in 1996 and heifers of Holstein Friesian and Deutsche Rotbunte in 1997, 10 animals per breed and year respectively. Average live weight was in the range of 430 to 525 kg. Mean daily live weight gain ranged from 540 up to 860 g with a rather big variation between individual animals. By means of combination of the two marker methods, the intake was determined to be 7 - 9 kg of organic matter and 75 - 100 MJ of metabolisable energy per head and per day on average. Considering the respective live weight and daily weight gain, results agreed in most cases well with the requirement figures from literature and feed tables. It was found that the differences between individual animals in live weight gain were much more caused by differences in feed intake rather than by different selectivity of grazing. Relationships were established between determined energy intake and daily live weight gain of the individual animals. The regression equations deduced from the obtained experimental data were applied for the estimation of the energy requirement of grazing cattle.