An important goal in dairy systems is to increase production while achieving environmental targets associated with lower nitrate leaching from soils. One approach is to identify forages that grow more at a given level of nitrogen (N) input and result in a lower N intake per kilogram dry matter (DM) consumed. However, while N responses have been well described for perennial ryegrasses, less information is available for alternative grasses, legumes and herbs. In the present study, conducted on the Canterbury Plains, New Zealand, six species (perennial ryegrass, Italian ryegrass, white clover, lucerne, chicory and plantain) were grown at six N-fertiliser rates ranging from 0 to 450 kg N/ha.year and managed under irrigation and cutting management. Herbage DM yield and N concentration were measured over 12 months. As N-fertiliser rate increased from 0 to 450 kg N/ha, annual herbage yield increased linearly (from 4794 to 14 329 kg DM/ha.year in grasses and from 7146 to 13 177 kg DM/ha.year in herbs). In contrast, annual herbage yield for legumes was unaffected by N-fertiliser rate and ranged from 11 874 to 13 112 kg DM/ha. Additionally, there were contrasting responses in herbage N concentration between species. At all N-fertiliser rates, herbage N concentration was highest in legumes (43.4 g N/kg DM), then herbs (30.7 g N/kg DM), and lowest in grasses (25.8 g N/kg DM). The N concentration of legume DM was unaffected by increasing N-fertiliser rate, whereas in grasses and herbs it increased. Results suggested that there were no benefits in using herbs instead of grasses for reducing N intake in livestock in an irrigated Canterbury environment.

Our objective was to determine if there were serious deleterious effects of wheat naturally contaminated with vomitoxin (deoxynivalenol) on nonlactating dairy cows. Comparisons were between two Quebec spring wheat sources contaminated with Fusarium graminearum in a feeding trial involving 10 nonlactating Holstein dairy cattle offered good quality hay for ad libitum intake supplemented with wheat-oats concentrate (1 kg concentrate/100 kg body weight). Initially, for 3 wk all cows were fed hay plus wheat-oats containing 1.5 mg vomitoxin/kg. Each week thereafter two more cows, chosen at random, were switched to a second wheat-oats concentrate containing higher mycotoxin concentration (6.4 mg vomitoxin/kg). After the last two cows had been on the latter diet for 6 wk, all cows were returned to the previous wheat-oats concentrate containing the lower mycotoxin concentration (1.5 mg vomitoxin/kg). No unusual symptoms of illness that might be attributed to the mycotoxin-contaminated wheat were observed. In body weight gains, the data reflected a linear growth pattern with no apparent effect of changing from low to high vomitoxin content in the concentrate. Generally, consumption of the wheat-oats ration containing 6.4 mg vomitoxin/kg was lower than the 1.5 mg vomitoxin/kg concentrate. The progressive, linear decrease of hay consumption was not affected by source of contaminated wheat-oats diet.

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.

Summary. Recently, many dairy farmers in Victoria have grown turnips as a summer fodder crop for lactating dairy cows. This paper reports on a 1 month experiment in which cows were individually fed indoors, and milk yield responses to feeding combinations of turnips and barley were measured. Forty cows in mid lactation were evenly allocated to 5 treatment groups. The control group were offered a basal diet of pasture hay and pasture silage which is similar to that available on many Victorian dairy farms during summer. Cows in the other 4 groups were offered the basal diet and various combinations of turnips and/or barley. Marginal milk responses from barley, turnips and a 50 : 50 mixture of turnips and barley were 0.62, 0.49 and 0.59 L/kg dry matter of supplement eaten. Milk composition of all groups was similar. Despite diets differing greatly in the proportions and physical form of dietary constituents, the mean milk production of each group was accurately predicted by their mean dry matter intake. Measurement of plasma minerals (calcium, magnesium, sodium, potassium and phosphorus) and rumen fluid pH showed that dietary treatments caused some significant (P<0.05) differences but all values were within the normal range. In this experiment, the milk production responses from barley, turnips and combinations of barley and turnips were similar. Since the cost of turnips is generally about half that of barley, it is concluded that turnips are an economic alternative to barley as a feed supplement for summer milk production.

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