Grape seeds and grape seed oil meal are poor in protein, rich in fibre and in tannins and therefore poorly digestible by ruminants. Grape seeds have a higher energy value than grape seed oil meal due to their higher lipid content and can be used at up to 20% in ruminant diets (Magnier, 1991). Some authors have considered that grape seed oil meal should not be fed to ruminants due to its poor nutritive value and that it should be used as carrier for molasses instead (El Boushy et al., 2000; Ferrando et al., 1966). However, studies have shown that grape seed oil meal can be included safely up to 10% in ruminant diets and higher inclusion rates have been reported (Magnier, 1991).
There is scarce information on the palatability of grape seeds and grape seed oil meal. It can be expected that the high tannin content is detrimental to palatability. A trial in Spain found that calves and dairy diets containing 30-50% solvent-extracted grape seed oil meal were not readily accepted at first, but were eaten readily later (Bayon, 1971).
Digestibility and degradability
A comparison of the fractions of grape pomace found that the seed fraction had the lowest in vitro OM digestibility: 13-16% vs 21-23 for the pulp fraction (Eraso Luca de Tena et al., 1992). In vivo OM digestibility values for grape seed oil meal were 24-28% (Cottyn et al., 1981). A value of 40% has been reported for the whole seeds (Magnier, 1991). Nitrogen degradability for both grape seeds and grape seed oil meal is in the 50-55% range (De Boever et al., 1984).
Effect on methane emissions
Grape seed oil meal has been investigated for its potential reducing effect on methane emissions. Using rumen simulation (Rusitec), corn distillers (DDGS) mixed with grape seed oil meal (up to 20% in the mixture, corresponding to 5% grape seed oil meal in the diet) was found to modulate favourably ruminal fermentation by lowering methane formation without adverse effect on fibre degradation. It may also be beneficial to rumen health and animal production by forming complexes with some rapidly degradable carbohydrates and thus may help to stabilize rumen pH in grain-rich diets (Khiaosa-ard et al., 2015).
Grape seed oil meal
A trial in Spain found that calves given diets containing 30% solvent-extracted grape seed oil had the same growth as calves fed a cereal-based diet. Diets could include up to 50% grape seed oil meal without detrimental effects on health and carcass characteristics (Bayon, 1971). A series of trials in Belgium concluded that 10% grape seed oil meal could be successfully incorporated in complete dry rations for bull fattening, resulting in good performance and carcass characteristics. Its feed value could be compared to that of linseed chaff. Treatment with NaOH did not improve its nutritional value (Cottyn et al., 1978; Cottyn et al., 1981).
Early trials found that whole grape seeds could be included up to 20% (Hogan et al., 1982) or even 30% (Accardi et al., 1977) in lamb diets. More recently, whole grape seed meal included in lamb diets at 10% dietary level produced weight gains and final live weights greater than those produced with the control feed. 20% dietary level gave feed conversion indexes similar to those obtained using the control feed. Slaughtering data, pH measurements, dissection data and meat chemical composition were not influenced by the type of feed. Increasing levels of grape seed meal decreased saturated fatty acids, increased unsaturated fatty acids and improved dietary characteristics of the meat with the best indices of atherogeniticy and thrombogenicity (Ragni et al., 2014).
In Italy, a series of experiments with dairy ewes investigated the effects of dietary inclusion of grape seeds (300 g/d), alone or in combination with linseed (220 g/d), on milk production and milk quality. These dietary treatments had no adverse effects on milk production and health status (Nudda et al., 2015). They decreased the milk concentration of de novo synthesized fatty acids C10:0, C12:0, and C14:0, showing that grape seeds could be useful to increase the concentration of polyunsaturated fatty acids with potential health benefits, especially when it was included together with linseed (Correddu et al., 2016). The addition of grape seeds (when combined with linseed) reduced the extent of light-induced oxidation of the total unsaturated fatty acids in milk (Correddu et al., 2015b). However, grape seeds were not effective in decreasing the biohydrogenation of dietary polyunsaturated fatty acids (Correddu et al., 2015a).
Grape seed oil meal
In France, grape seed oil meal given as sole feed to sheep caused weight loss and it was concluded that it was not suitable for sheep feeding (Ferrando et al., 1966). In Cyprus, lambs could be fed diets containing 40% grape seed oil meal with no detrimental effect on weight gain. However, feed intake was higher than for lambs fed the control barley-based diet and feed conversion efficiency was lower. The increased intake was reflected in increased gut-fill and correspondingly lower carcass yield (Mavrogenis et al., 1973).