Intake and growth of steers offered different allowances of autumn grass and concentrates

The aim of this experiment was to quantify the relationship between autumn grass supply and concentrate supplementation level on grass intake and anim al performance. Once hundred and ten continental steers (567 kg) were assig ned to 10 treatments. The experimental design was a three grass allowances (6, 12 and 18 kg dry matter (DM) per head daily) by three concentrate level s: (0, 2.5 and 5 kg per head daily) factorial with a positive control group offered concentrates and libitum and no grass. Grass allowance was offered daily and concentrates were given individually. The experiment began on 22 August and all animals were slaughtered after a mean experimental period o f 95 days. Grass intake was calculated using the n-alkane technique and die t digestibility using ytterbium acetate as an indigestible marker. There wa s an interaction (P < 0.05) between grass allowance and concentrate level f or grass intake. At the low grass allowance there was no effect of offering animals supplementary concentrates on grass intake, at the medium and high grass allowances, supplementary concentrates reduced grass intake by 0.43 and 0.81 kg DM respectively per kg DM concentrate offered. Increasing grass allowance increased (P < 0.001) complete diet organic matter (OM) digestib ility at all concentrate levels and supplementary concentrates increased (P < 0.001) complete diet OM digestibility only at the low grass allowance. B oth offering animals supplementary concentrates (P < 0.001) and increasing daily grass allowance (P < 0.001) increased their carcass growth rate. Rela tive to the animals offered the low grass allowance and no concentrate, sup plementing with concentrate increased carcass growth by 116 g/kg concentrat e DM eaten whereas increasing the grass allowance, increased carcass growth by 38 g/kg DM grass eaten. As a strategy for increasing the performance of cattle grazing autumn grass, offering supplementary concentrates offers mo re scope than altering grass allowance.