Many farmers in southern Victoria grow fodder turnips as a summer feed for
lactating dairy cows. This paper reports on 2 experiments that measured the
milk yields and liveweight changes of cows offered a basal forage diet and
combinations of turnips, barley and protein supplements (cottonseed meal or
lupins).
A stall feeding experiment was conducted over 26 days with 40 Friesian cows in
mid lactation offered 1 of 5 dietary treatments. All cows were offered 10 kg
DM/day of a basal diet comprising pasture, pasture hay and pasture silage
which is similar to that available on many southern Victorian dairy farms
during summer. Cows in a control group did not receive additional feed
supplements. Cows in the other 4 groups were offered a supplement of 5 kg
DM/cow.day of either turnips, barley or a mixture containing 3 kg
DM/cow.day of turnips and 2.0 kg DM/cow.day of either crushed lupins
or cottonseed meal. The marginal milk responses from barley, turnips, turnips
+ lupins and turnips + cottonseed meal were 0.80, 0.92, 1.15 and
1.00 L/kg DM of supplement eaten. There were no significant differences
(P>0.05) in the liveweight changes of the
supplemented groups. Samples of the feeds used in this experiment were placed
in nylon bags and incubated in the rumen of non-lactating dairy cows. The
‘Ørskov’ protein degradation parameters for these feeds are
compared with the published values for a range of Australian feeds. The rate
and extent of degradation of protein from the turnip leaves, turnip bulbs and
crushed barley were all similar.
A grazing experiment was conducted over 65 days with 56 Friesian cows in mid
lactation, offered 1 of 4 dietary treatments. All groups were allowed to graze
pasture (5 kg DM/cow.day), were offered 3 kg DM/cow.day of pasture
silage and were fed different combinations of barley, cottonseed meal and
lupins. In addition, 3 of the groups separately strip-grazed turnips (about 5
kg DM/cow.day). The group fed a supplement of 8.0 kg/cow.day of barley
yielded similar quantities (18.3 L/cow.day) of milk and milk constituents
as another group fed 4.0 kg DM/cow.day of barley and 4.5 kg DM/cow.day
of turnips. Furthermore, when either 1.5 kg DM of cottonseed meal or 2.0 kg of
lupins were fed in place of barley, milk yield increased by 1.4 L/cow.day.
Dietary treatment had no significant (P>0.05) effects
on liveweight changes. From this grazing experiment it is concluded that
turnips can be used as a cheaper alternative to barley in order to maintain
high levels of milk production in summer–autumn. We estimate that if the
above quantities of protein supplement were fed with turnips, at 1997–98
prices, lupins would increase profits by 12 cents/cow.day, but there would
be no financial benefit from the cottonseed meal.
The findings from both experiments show that supplements of rumen-degradable
protein (lupins) can produce an economic milk response when fed to cows on
typical summer diets (pasture/silage/barley and turnips) in southern
Victoria.
Integrating spot short-term measurements of carbon emissions and backward dietary energy partition calculations to estimate intake in lactating dairy cows fed ad libitum or restricted
