Traditionally in Mediterranean vineyards vine leaves and shoots have been grazed by sheep and goats after the harvest. They also provide feed when pasture is scarce or of poor quality (Magnier, 1991; Kamalak, 2007). However, they generally have a poor nutritive value, roughly similar to hay for the leaves and to straw for the shoots, and should, therefore, be fed to livestock with low nutritional needs (Magnier, 1991). As a general rule, they should not be fed alone but supplemented with sources of energy and protein (Pinto, 1990). In spite of their widespread use, information about the use of grape leaves and shoots is limited.
Palatability and intake
The palatability of grape leaves and vine shoots is variable and is probably positively correlated to the amount of green matter they contain. Fresh vine leaves appear to be very palatable: the spontaneous grazing of vine leaves by sheep used for vineyard weeding is such a problem that aversion training methods (based on associating nausea with leaf consumption) have been developed to prevent this behaviour (Fusté et al., 2014; Burritt et al., 2013). Voluntary DM intake of female sheep offered grape leaves was also relatively high (1 kg/day), and the tannin content did not appear to be a problem (Romero et al., 2000). Conversely, some authors report that vine shoots are of low palatability and that salt should be added to increase consumption (Magnier, 1991). DM intake of vine shoots in sheep was found to be low, in the 28-29 g/kg W0.75 range for 35-55 kg sheep, below the minimum requirements and less than half that of fresh leaves (Vonghia et al., 1983). Ensiled vine shoots mixed with bran, molasses and middling have been reported as highly palatable for all classes of livestock (Pau, 1940).
Digestibility and degradability
The digestibility of fresh grape leaves is generally medium to good, though information about it is scarce. In Turkey, in vitro DM digestibility of leaves ranged from 60 to 75% depending on grape variety, fibre and tannin contents (Kamalak, 2005). In Spain, in vivo OM digestibility in sheep was 47%, well below that of oat-vetch hay (61%) (Romero et al., 2000). The OM digestibility of vine shoots is generally low though highly variable. A Tunisian trial reported a very low value of 15%, while a Spanish trial reported much higher values: 44-53% (Rouaissi, 1986; Vonghia et al., 1983). A DM digestibility value of 40% was reported for ensiled vine shoots (Rebolé et al., 1988). OM degradability of vine shoots was slightly higher in buffaloes (25%) than in cattle (23%) (Settineri et al., 1995). Nitrogen digestibility of leaves and vine shoots are sometimes negative and, therefore, unreliable. Nitrogen degradability values reported for leaves and vine shoots are in the 45-55% range (Gurbuz, 2007; Molina-Alcaide et al., 2008).
Several Italian trials have tried to increase the feeding value of vine shoots by treating them with urea (Pinto et al., 1985; Marsico et al., 1985) or NaOH (Pinto et al., 1983), but neither method was satisfactory because of cost and limited efficiency.
In Italy, dried and ground vine shoots fed to fattening calves at up to 30% of the diet gave satisfactory feed intake, growth and carcass characteristics (Bosticco et al., 1969). A trial with Friesian calves showed that feeding diets containing vine shoots collected one month after pruning resulted in a relative improvement in production, while dry vine shoots collected 5-12 months after pruning were more lignified and less digestible (Tartari et al., 1979a; Tartari et al., 1979b).
In Romania, wool growth and body weight of ewes during pregnancy and lactation, and condition and growth of their lambs, were about the same with 1.5 kg ensiled vine crop residues as with feed based on maize silage (Timariu et al., 1965). A series of Italian trials have assessed the value of vine shoots for sheep. The general conclusion was that vine shoots had limited palatability and digestibility and should preferably be used fresh and chopped in diets balanced for energy and protein, at a maximum of 33% of the diet (Pinto et al., 1983; Vonghia et al., 1983; Pinto et al., 1985; Marsico et al., 1985; Vonghia et al., 1985; Pinto, 1990).