Two 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.

In order to establish the response of dairy cow performance to concentrate supplementation in contrasting grazing conditions and for cows differing in milk yield at turn-out, three experiments were conducted. Each year, two levels of herbage allowance were studied in interaction with four (experiment 1) or three (experiments 2 and 3) levels of concentrate on two groups of 30 to 40 mid-lactation Holstein cows producing between 20 and 46 kg milk at turnout. Amount of concentrate and herbage allowance ranged from 0 to 6 kg fresh weight and from 12 to 22 kg dry matter (DM) per cow per day respectively. The supplementation led to average responses, per kg DM concentrate, of 104 kg milk, +66 g/day body-weight gain, +0·19 g/kg milk protein and -0·57 g/kg milk fat. These responses remained linear up to 4 or 6 kg according to the years and treatments. The response to the concentrate did not vary with the milk yield or composition at turn-out. The increase in the herbage allowance from 12 to 16 kg DM per cow per day (experiment 1) improved milk yield (+1·2 kg/day) and milk protein (+0·7 g/kg) while the increase from 16 to 22 kg DM (experiments 2 and 3) had less effect (+0·5 kg/day milk yield and +0·4 g/kg milk protein). There was no clear interaction between concentrate supplementation and herbage allowance. Under the usual conditions of spring pasture, with cows in mid lactation, the use of a constant level of concentrate at grazing proves to be a technique of some interest.