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 ad 34.1 kg), was set up to examine the effect of rapid wilting of pere nnial ryegrass herbage, and type of forage additive applied, prior to ensil ing on energy utilisation by growing cattle. The forages used were either u nwilted or wilted for 26 h (mean DM 193 and 450 g/kg respectively) each con served using either a bacterial inoculant to stimulate, or formic acid to r estrict, fermentation. Six feeding treatments, comprising the two unwilted silages (inoculated and acid treated) each offered ad libitum, the two wilt ed silages (inoculated and acid treated) each offered ad libitum and restri cted to 0.7 of ad libitum intake were offered to two animals per period dur ing a 19-day feeding period. Ration digestibility and data on energy exchan ge determined using indirect open-circuit respiration calorimetry, were rec orded during the last 9 and 3 days of each period respectively. The data we re analysed by analysis of variance according to the two silage types (wilt ed, unwilted), *2 additive (inoculant, acid) factorial structure to test fo r the main effects of each factor and interactions. There were no significa nt interactions in any of the measurements. Regression analyses were used t o compare the energy utilisation variables for the wilted and unwilted sila ges at equal ME intakes, At equal ME intakes heat production, energy retent ion and efficiency of ME utilisation for tissue gain k(g) were not influenc ed by wilting of the forage. Neither did additive type (stimulant, restrict or) influence these variables. Overall regression analysis of energy retent ion against ME intake indicated a maintenance ME requirement of 0.62 MJ kg W-0.75 and k(g) of 0.39. These values support the recent published figures from this Institute and add weight to the view that maintenance energy requ irements are above these traditionally adopted in the UK feeding systems. ( C) 1999 Elsevier Science B.V. All rights reserved.