Energy value and digestibility
Metabolizable energy was about 8.7 MJ/kg DM (NDF 48% DM) in foliage harvested in mid-October (Lindberg et al., 1986). Net energy for lactation was 5-6 MJ/kg DM for forage harvested late in October prior to tuber harvesting. The latter values were similar to the ones obtained on sunflower green fodder (Petkov et al., 1997a).
Cell wall and lignin of the green foliage increased the proportion of rumen undegradable fractions and thus decreased the DM and OM rumen degradability (Lindberg et al., 1986), as well as the in vivo OM digestibility (Petkov et al., 1997a). At the flowering stage, the whole plant showed an in vitro DM digestibility of about 60% that was lower than that observed for sunflower forage (Seiler, 1993). The substitution of alfalfa by up to 30% of Jerusalem artichoke foliage at full bloom did not affect the in vitro digestibility of the diet (Fazaeli et al., 2009).
Rumen nitrogen degradability of Jerusalem artichoke fodder depends on the stage of maturity. Reported values for the effective degradability of N were about 67% for the whole plant, i.e. around 90% of that of alfalfa (Lindberg et al., 1986) and 65% for Jerusalem artichoke leaves, similar to alfalfa (Ma et al., 2010).
Compared to maintenance requirements of ruminants, the mineral contents of Jerusalem artichoke forage at the flowering stage appear adequate for Ca, Mg, K, but inadequate for P, and excessive in terms of the Ca:P ratio (Seiler et al., 2004; Seiler et al., 2006).
Animal performance and palatability
Few studies have investigated the effect of feeding Jerusalem artichoke forage on animal performance. Moreover, because of the high variability of its composition and nutritive values, recommendations for its utilization as green fodder for ruminants can differ greatly. Jerusalem artichoke can be either regarded as fully suitable for intensive feed production (Nadezhkin, 1997) or only used as a supplement (Petkov et al., 1997a). For dairy cows, fresh Jerusalem artichoke tends to increase lactose and fat contents in the milk, but should not be included at more than 20 kg fresh material (6-7 kg DM) per day (Kuppers-Sonnenberg, 1977). In field trials, Jerusalem artichoke forage was either completely or nearly completely rejected by grazing lambs when compared to other perennial grasses (Marten et al., 1987). For roe deer, the quantity of Jerusalem artichoke fodder should be limited in practice (Ma et al., 2010). The mineral content of Jerusalem artichoke varieties (especially sulphur, molybdenum, chlorine and lead) and the total phenol content of leaves could influence the feeding preference of fallow deer (Gleich et al., 1998).
The aboveground parts of Jerusalem artichoke can be stored as silage for winter feeding, which is more palatable than dried forage (Kays et al., 2008b). However, Jerusalem artichoke silage contains less nutrients, and in vitro organic matter digestibility and energy values are lower compared with the fresh plant. For this reason Jerusalem artichoke whole plant is regarded as a green forage, which can be ensiled if necessary (Karsı et al., 2009). Addition of 5% molasses into the green mass improved fermentation and increased digestibility of the Jerusalem artichoke silage (Bingöl et al., 2010). When molasses is added to the Jerusalem artichoke silage, dry matter intakes were higher than that would have been predicted for other grass silages of similar composition (Hay et al., 1992).
Energy value, digestibility and degradability
The energy and nitrogen digestibilities of Jerusalem artichoke tuber meal measured in dairy cows were 73 and 62% respectively, and the net energy for lactation was 5.5 MJ/kg DM (Zhao et al., 2011). In sheep, a much higher net energy value of 7.7 MJ/kg DM (ME 12.7 MJ/kg DM) was recorded, comparable to that estimated for root crops such as fodder beets (Petkov et al., 1997b).
Effective rumen degradability of the tuber nitrogen is very high (almost 80%, Chapoutot, 1998). The NDF undegradable fraction is lower than 30% (Chapoutot et al., 2010). The fructosan fraction is highly fermentable in the rumen, more so than cellulose, starch and pectins, resulting in a higher in vivo and in vitro digestibility compared to other feeds rich in starch or fiber, but also in higher methane emissions (Hindrichsen et al., 2004; Hindrichsen et al., 2005). Tubers induced the highest volatile fatty acids and lactate accumulation, with the largest drop in pH (Vervuert et al., 2005).
The K:(Ca+Mg) ratio of Jerusalem artichoke tubers is more than twice higher than the prescribed ratio for cattle feed (Terzic et al., 2012). The high content of potassium could explain the higher urine volume observed when increasing the inclusion rate of tubers in the diet (Hindrichsen et al., 2006). Inversely, the Ca:P ratio in tubers (about 1:1) corresponds to the desired ratio for cattle feed, contrary to the leaves that contain much more Ca than P.
Use of Jerusalem artichoke tubers in cattle
When included up to 30% in the diet of dairy cows, the Jerusalem artichoke meal did not change significantly milk yield and milk component contents (Zhao et al., 2011). In dairy cows, using Jerusalem artichoke tubers as a concentrate in a forage/concentrate (1:1) diet caused higher urinary energy loss but better energy utilization compared to soybean hulls, and did not result in clear differences in energy retention (Hindrichsen et al., 2006).
In growing steers, Jerusalem artichoke tubers could substitute for 20% of steam-flaked maize without altering DM and protein digestibility and nitrogen retention (Bramble et al., 2000).