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

Abstract

AbstractTwo groups of grazing lactating dairy cows (no. = 10) were offered straw/sugar-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 respectively. 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 degradability values of 10·4 and 8·4 MJ/kg DM and 0·48 and 0·42 for mixture LS and HS, respectively. In experiment 1, the mixtures were offered for 1 h after each milking while in experiment 2 the amount of LS available was restricted to the intake of the HS mixture. The animals continuously grazed a perennial ryegrass sward with sward height maintained at 7·5 and 6·9 cm respectively for experiment 1 and 2. Forage intakes in both experiments were measured using the n-alkane technique. In experiment 1, intakes of the forage supplement 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 treatments LS and HS respectively. No significant differences in terms of time spent grazing, ruminating and eating forage supplement were observed. No significant differences in terms of animal performance were observed. In experiment 2 intakes of the forage supplements were 2·8 kg DM per day for both treatments while herbage intake was 13·0 and 13·2 kg DM per day (s.e.d. = 110) 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 detected. It was concluded that under conditions when herbage was readily available, higher amounts of high energy/high degradability forage supplement were consumed than of low energy low degradability forage supplements. However, total dry matter intakes were equal. Intake from forage supplements seem to be affected by short-term fill effects in this situation.