The effects of supplementing grazing dairy cows with straw-based mixtures of differing composition

Two groups of grazing lactating dairy cows (no. = 10) were offered straw/su gar-beet pulp mixtures of different straw and sugar-beet pulp content. The low straw mixture (LS) contained 310, 592, 65, 9 and 24 g/kg dry matter (DM ) of barley straw, sugar-beet pulp, cane molasses, urea and minerals respec tively. The high straw mixture (HS) contained 540, 359, 65, 12 and 24 g/kg DM of these ingredients. This resulted in metabolizable energy and DM degra dability values of 10.4 and 8.4 MJ/kg DM and 0.48 and 0.42 for mixture LS a nd HS, respectively. In experiment 1, the mixtures were offered for 1 h aft er each milking while in experiment 2 the amount of LS available was restri cted to the intake of the HS mixture. The animals continuously grazed a per ennial ryegrass sward with sward height maintained at 7.5 and 6.9 cm respec tively for experiment 1 and 2. Forage intakes in both experiments were meas ured using the n-alkane technique. In experiment 1, intakes of the forage s upplement were 5.3 and 2.3 kg DM per day (s.e.d. = 0.51, P < 0.001), while herbage intake was 11.5 and 14.5 kg DM per day (s.e.d. = 0.77, P = 0.004), resulting in total forage intakes of 16.9 and 16.7 kg DM per day for treatm ents LS and HS respectively. No significant differences in terms of time sp ent grazing, ruminating and eating forage supplement were observed. No sign ificant differences in terms of animal performance were observed. In experi ment 2 intakes of the forage supplements were 2.8 kg DM per day for both tr eatments while herbage intake was 13.0 and 13.2 kg DM per day (s.e.d. = 1.1 0) resulting in total daily intakes of 15.8 and 16.0 kg DM (s.e.d. = 1,24) for treatment LS and HS, respectively. No significant differences in terms of grazing time, rumination time or animal performance were defected. It wa s concluded that under conditions when herbage was readily available, highe r amounts of high energy/high degradability forage supplement were consumed than of low energy low degradability forage supplements. However, total dr y matter intakes were equal. Intake from forage supplements seem to be affe cted by short-term fill effects in this situation.