This paper reports the results of three experiments designed to attempt to
improve the efficiency of milk production from diets based on a 1 : 2 dry m
atter (DM) mixture of grass silage and whole-crop wheat (WCW) harvested at
550 to 600 g DM per kg and treated with 40 g urea per kg DM. In the first e
xperiment a control diet of the forage mixture offered ad libitum with 9 kg
fresh weight (FW) per day of a concentrate mix was compared with seven tre
atments in which the forage or the concentrates were varied. Eight multipar
ous cows were used in a four-period incomplete change-over design with 4-we
ek periods. Caustic treatment of the WCW increased DM intake (P < 0.001) bu
t tendencies for higher yields of milk and milk protein were not significan
t. Replacement of 2 kg FW concentrates per day by the same weight of molass
es as a 24-h pre-soak of the forage (molasses pre-treatment) or added to th
e forage at feeding increased DM intake (P < 0.001) but did not increase mi
lk yield or yield of milk solids. Molasses pre-treatment and molasses added
to the concentrates reduced milk protein concentration (P < 0.05). Replace
ment of 2 kg FW concentrates per day by the same weight of ground wheat inc
reased DM intake when added to the concentrates (P < 0.001) but not when ad
ded to the forage and milk yield was unaffected by either method of additio
n. The ground wheat tended to result in higher milk protein concentrations
than the molasses. Increasing the digestible undegradable protein content o
f the concentrates had no significant effect on food intake or milk product
ion. In the second experiment diet digestibility and energy and nitrogen (N
) balance were measured for the control diet and three of the treatments fr
om experiment I in four multiparous cows in a 4 X 4 Latin-square experiment
with 5-week periods. There were no significant effects on food intake or m
ilk yield. Caustic treatment reduced starch digestibility (P < 0.001) and i
ncreased neutral-detergent fibre (NDF) digestibility (P < 0.05) but had no
effects on energy utilization. It also reduced N intake (P < 0.01) and urin
e N losses (P < 0.001) by reducing the ammonia concentration of the WCW. Mo
lasses added to the forage or concentrates reduced milk protein concentrati
on (P < 0.05) and digestibility of both starch and NDF (P < 0.05) but energ
y utilization was unaffected. In a further Latin-square experiment with the
same treatments and four fistulated lactating cows, caustic treatment redu
ced daily mean ammonia concentration (P < 0.01) and increased daily mean pH
(P < 0.01) in the rumen. It is concluded that these treatments did not gen
erally improve the value of WCW although caustic treatment increased milk y
ield and milk protein yield consistently but not significantly. However pra
ctical problems may limit its use on the farm. Urea-treated WCW must be acc
epted as being a relatively low-energy food although with high intake chara
cteristics, and future work should concentrate on evaluating WCW harvested
at an earlier stage of maturity.