The effect of the proportion of clover in the diet (200, 500 or
800 g/kg
total dry matter (DM)) on milk production of cows housed indoors and fed
on a
mixture of perennial rye-grass and white clover was measured in mid (Expt
I) and
late (Expt II) lactation. Higher clover contents increased the nutritive
value of the
diets, resulting in increased energy and protein intakes. DM intakes of
cows offered
500 or 800 g clover/kg DM diets ad lib. (Expt I and Expt II,
Period 1) were not
significantly different but were 11–17% greater
(P<0·05) than intakes of cows fed
on 200 g clover/kg total DM diets. Cows offered restricted allowances
(Expt II,
Period 2) had similar intakes irrespective of diet. In Expt I cows fed
on 500 or 800 g
clover/kg DM diets ad lib. produced 30 or 33% respectively
more milk
(P<0·05)
than cows fed on 200 g clover/kg total DM diets. During Expt II, Period
1, cows fed
on 500 or 800 g clover/kg DM diets ad lib. produced 18 or
16% more milk
(P<0·05)
respectively than cows given 200 g clover/kg total DM diets. In both
these
experiments the increased milk yields were due to increased intake and
the higher
nutritive value of the high clover diets. There was no difference in the
feed conversion
efficiencies of cows if maintenance energy requirements were taken into
account.
However, cows on restricted allowances (Expt II, Period 2) showed no significant
difference in milk yield, indicating that the effect of increased nutritive
value was
very slight. There were no consistent effects on milk fat, protein or lactose
concentrations. Concentrations of blood and milk urea increased as the
clover
content of the diet increased (Expt 1 only), and this was associated with
increased
milk non-protein N and a decreased ratio of casein N[ratio ]total N. Both
trials indicated
an optimum clover content in the diet for milk production of 600–700
g/kg total DM.