Abstract

<jats:p>
Summary. Two experiments were conducted on feeding grain
supplements to dairy cows during summer. In experiment 1, dairy cows in
mid–late lactation were offered one of 2 pasture allowances (about 20
and 40 kg DM/cow.day) with and without a supplement of a grain mix (5 kg
of a 70 : 30 mixture of barley and lupins). This experiment was conducted
twice over 2 consecutive summer–autumn periods (years 1 and 2). Milk
yields were higher at the high pasture allowance and with grain feeding. The
marginal response to grain feeding (kg milk/kg grain DM consumed) was 0.7
at both pasture allowances in year 1, and 1.1 and 0.8 at the low and high
pasture allowance, respectively, in year 2. Diet had no significant effect on
milk composition. Pasture intake was reduced by supplementary feeding and the
level of substitution depended on pasture allowance.
The alkane-based and sward sampling techniques were used to estimate pasture
intake and diet digestibility. Estimates of pasture substitution, based on
measurements made with the alkane technique, were 0.3 and 0.6 kg DM reduction
in pasture/kg DM grain consumed at the low and high pasture allowance,
respectively, in both years. In year 1, the pasture substitution measured with
the pasture difference method was 1 kg pasture DM/kg grain DM at both
pasture allowances. In year 2, estimates of substitution calculated using the
pasture difference method were 0.2 and 0.5 kg pasture DM/kg grain DM at
the low and high pasture allowance respectively.
In the second experiment (year 3), the effects of level of feeding barley on
pasture intake, diet digestibility and milk production were measured during
summer. The 4 levels of grain consumed were 0, 1.8, 3.4 and 6.7 kg barley
DM/cow. day. Higher grain intake resulted in higher milk yield, higher
protein concentration and yields of fat, protein and lactose. Milk yield
responses per kilogram of barley diminished from 1.6 at the low barley intake
to 0.8 kg milk/kg barley DM at the highest barley intake. It is suggested
that higher levels of substitution and a potentially less efficient use of
grain contributed to the poorer production responses at higher levels of grain
feeding.</jats:p>