The summer nutrition of weaner sheep: The voluntary feed intake, body weight change, and wool production of sheep grazing the mature herbage of sown pasture in relation to the intake of dietary energy under a supplementary feeding regime

The effect on herbage intake of feeding energy-rich supplements to weaner sheep during periods of summer drought was examined in two field studies in a Mediterranean environment. The total intake of digestible energy (DE) and of dry matter (DM) by each sheep was also measured, and the relation of DE intake to body weight, body weight change, and wool production was studied under these supplementary feeding regimes. In both experiments the sheep grazed sown pastures which provided low quality mature herbage (DM digestibility 45-49 %) in plentiful amounts (> 800 kg DM/acre). A new method of estimating herbage digestibility based on direct weighings of the animal before and after a period of restricted grazing, was used in one experiment. The estimate of DM intake by this method was less by 5% than the value derived from a regression equation based on faecal nitrogen concentration. The results of the two studies were in good agreement. For each 100 g supplement (up to levels of 400 g DM/day) the intake of herbage decreased by 65-69 g. The daily digestible energy intake needed to maintain wool-free body weight was 176 kcalDE/kg W0.75 (equivalent to about 144 kcal metabolizable energy/kg W0.75). This value is substantially higher than the results recorded for pen-feeding experiments but is comparable with other results recorded for the grazing sheep. The production of each additional gram of clean wool was associated with an increased intake of 52 g digestible DM (230 kcal DE). However, because herbage intake was reduced when a supplement was fed, it was in fact necessary to provide 86 g DE as a supplement (i.e. 65 % more than is indicated by the previous value) in order to produce an additional gram of clean wool.