Turnips and protein supplements for lactating dairy cows

Abstract

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.