The influence of wilting and forage additive type on the energy utilisation of grass silage by growing cattle

A two period, partially balanced change-over design study, using 12 steers (416 sd 34.1 kg), was set up to examine the effect of rapid wilting of perennial ryegrass herbage, and type of forage additive applied, prior to ensiling on energy utilisation by growing cattle. The forages used were either unwilted or wilted for 26 h (mean DM 193 and 450 g/kg respectively) each conserved using either a bacterial inoculant to stimulate, or formic acid to restrict, fermentation. Six feeding treatments, comprising the two unwilted silages (inoculated and acid treated) each offered ad libitum, the two wilted silages (inoculated and acid treated) each offered ad libitum and restricted to 0.7 of ad libitum intake were offered to two animals per period during a 19-day feeding period. Ration digestibility and data on energy exchange determined using indirect open-circuit respiration calorimetry, were recorded during the last 9 and 3 days of each period respectively. The data were analysed by analysis of variance according to the two silage types (wilted, unwilted), *2 additive (inoculant, acid) factorial structure to test for the main effects of each factor and interactions. There were no significant interactions in any of the measurements. Regression analyses were used to compare the energy utilisation variables for the wilted and unwilted silages at equal ME intakes. At equal ME intakes heat production, energy retention and efficiency of ME utilisation for tissue gain kg were not influenced by wilting of the forage. Neither did additive type (stimulant, restrictor) influence these variables. Overall regression analysis of energy retention against ME intake indicated a maintenance ME requirement of 0.62 MJ kg W0.75and kg of 0.39. These values support the recent published figures from this Institute and add weight to the view that maintenance energy requirements are above those traditionally adopted in the UK feeding systems.