Turnips and Protein Supplements for Lactating Dairy Cows
Moate, PJ and Dalley, DE and Roche, JR and Grainger, C and Hannah, M and Martin, K, Turnips and Protein Supplements for Lactating Dairy Cows, Australian Journal of Experimental Agriculture, 39 pp. 389-400. ISSN 0816-1089 (1999) [Refereed Article]
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 'φrskov' 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.