Twelve young Friesian bull calves were individually fed for 6 weeks on one of three diets containing buttermilk powder (BMP): (i) a low energy diet (Low) to provide for 0.45 kg live-weight gain (LWG) /day; (ii) a diet isonitrogenous to (i) of BMP supplemented with beef tallow to provide for 0.68 kg LWG/day (High Tallow); (iii) an isoenergetic diet to (ii) consisting of BMP alone to provide for 0.68 kg LWG/day (High). Energy and nitrogen (N) balance techniques were used to study the utilisation of tallow as a supplementary source of dietary energy. Tallow supplementation reduced the incidence and severity of diarrhoea. There were no treatment effects on the apparent digestibilities of gross energy, N, or ether extract (EE), the average coefficients being 94.9, 91.1, and 93.5 respectively. Digestibility of EE increased from 91.7 at 3 weeks to 95.0 at 6 weeks, (P 0.01). Live-weight gains were not significantly affected by treatments. Gross energy intake and energy retention (measured by indirect calorimetery) by the calves were in the order High i= High Tallow Low (P 0.01). The pooled efficiency of utilisation of metabolisable energy (ME) above maintenance was 78 and the estimated requirement for maintenance was 0.556 MJ ME/(kg0.75day). Nitrogen intake was in the order High High Tallow = Low (P 0.01), whereas N retention was in the order High High Tallow Low (P 0.05). Percentage of digested N retained was significantly higher in High Tallow than in the other two treatments (P 0.01).
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