The effect of concentrate level on the intake of grass silages by ewes in late pregnancy

Abstract

In two experiments, six silages were offered either alone or with constant daily levels of a barley-based concentrate (450 or 900 g fresh weight per ewe) to Finn Dorset ewes carrying between one and four foetuses in the last 6 weeks of pregnancy. The silages (SI to S3, experiment 1 and S4 to S6, experiment 2) had dry matter (DM) concentrations of 256, 190, 278 and 294, 216, 201 g/kg fresh weight and crude protein (CP) concentrations of 106, 164, 212 and 119, 148, 194 g/kg DM. Mean metabolizable energy (ME) concentrations of the silages (digestible energy × 0·81), in weeks 16 and 20, were 9·2, 10·3, 12·0 and 8·8, 10·9, 11·0 MJ/kg DM. Total ME intakes were 12·6, 13·5, 18·6 and 14·5, 15·1, 16·8 MJ/day in week 16 of gestation and were 11·6, 11·2, 17·2 and 12·2, 11·8, 13·3 MJ/day in week 20. Total ME intakes were increased by offering higher levels of concentrates and for levels of 0, 450 or 900 g/day these were 12·3, 14·8, 17·9 MJ/day in week 16 and 9·6, 12·8, 15·5 MJ/day in week 20. Intakes were similar for ewes carrying twins or multiples in experiment 1, but in experiment 2, intakes by ewes with twins or multiples were proportionately 0·97 and 0·85 of those for ewes with singles. Replacement rates of forage by concentrates were —0·09, —0·08, —0·60 and —0·06, —0·25, —0·38 g silage organic matter (OM) per g concentrates OM for silages SI to S3 and S4 to S6. Only on silage S6 did the replacement rate differ significantly from zero.