THE EFFECT OF DIFFERING FORAGE CONCENTRATE RATIO AND RESTRICTING FEED-INTAKE ON THE ENERGY AND NITROGEN-UTILIZATION BY BEEF-CATTLE/

Six Charolais cross steers (mean live weight 459 kg) were used in a pa rtially balanced changeover design experiment with four 4-week periods . The energy and nitrogen utilization by cattle offered diets differin g in forage:concentrate (F:C) ratio, but of equal metabolizable energy intake (MEI), were measured. The three diets were (1) high digestibil ity (D) grass silage offered ad libitum; (2) low D silage offered ad l ibitum and supplemented with sufficient concentrates to provide the sa me MEI as (1); (3) high D silage supplemented with the same F:C ratio as (2) and with intake restricted to the same MEI as (1) and (2). Thes e three diet types were offered at two levels of energy intake, the hi gher level of energy intake having been achieved by adding further con centrates to diets 1 to 3. Gross energy intake (GEI) and faecal, urina ry and methane outputs and heat productions were measured in respirati on chambers for three days at the end of each period. When values were adjusted to equal MEI across the three diets, animals offered the res tricted diet produced significantly less methane, expressed as a propo rtion of GEI (P < 0.001), than those offered the other two diets. Howe ver, there was no difference in energy retention or the efficiency of utilization of energy for growth between the three diet types used in this study. (C) 1997 Elsevier Science B.V.