The combined effects of animal species (sheep versus cattle) and level of feeding on digestible and metabolizable energy concentrations in grass-based diets of cattle

A total of 317 dairy and beef cattle, offered grass silage-based diets, have been subjected to energy metabolism measurements in calorimetric chambers in 11 feeding experiments at this Institute. In addition the silages (no. = 33) were also given individually to sheep as a sole food at maintenance feeding level for measurement of energy intake and outputs (faeces and urine). The digestible (DE) and metabolizable (ME) energy concentrations of mixed diets for sheep at maintenance were estimated using these measured silage data, predicted silage methane energy output and tabulated energy values of concentrates. The objective of the present study was to use treatment mean data (no. = 59), derived from the cattle (production level) (ME(prod) or DE(prod)) and the sheep (maintenance level) (ME(maint) or DE(maint)), to evaluate the combined effects of animal species and level of feeding on dietary ME or DE concentration. The mean-square prediction error technique and the sensitivity test both indicated that there was little bias derived from the deviation of the slope (line bias) when relating ME(prod) (DE(prod)) with cattle to ME(maint) (DE(maint)) with sheep. Relating feeding level to the decline in ME or DE concentration (from maintenance to production level) revealed that the constant had no significant effect on the relationship, suggesting that there was little difference in dietary ME or DE concentration between sheep and cattle when given food at maintenance. ME(prod) and DE(prod) were significantly related to ME(maint) and DE(maint) (P < 0.001) respectively. These two relationships were however influenced (P < 0.001) by level of feeding above maintenance (FL-1). There was little effect of silage DM proportion in the total diets (S/T) on the depression of ME concentration from maintenance to production levels, while this effect on the depression of DE concentration was significant (P < 0.001). Therefore, the following two equations are recommended to calculate ME(prod) and DE(prod) concentrations respectively for cattle using data obtained with sheep at maintenance. Alternatively, with each unit increase in feeding level above maintenance, dietary ME and DE concentrations respectively were reduced by proportionately 0.016 and 0.025 for grass silage-based diets, irrespective of the effect of forage proportion on the latter.