Grape seeds and grape seed oil meal are low in protein, rich in fibre and tannins and, therefore, poorly digested 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). It has been suggested that grape seed oil meal should not be fed to ruminants due to its low nutritive value, and instead it should be used as a carrier for molasses (El Boushy et al., 2000; Ferrando et al., 1966). However, studies have shown that grape seed oil meal can be included safely at up to 10% in ruminant diets, and higher inclusion rates have been reported (Magnier, 1991).
Palatability
There is little 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 calf and dairy cow diets containing 30-50% solvent-extracted grape seed oil meal needed an introductory phase to overcome palatability problems (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 technique, corn distillers grain (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 rumen fermentation by lowering methane production without adverse effects 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).
Beef cattle
Grape seed oil meal
In Spain, a trial found that calves given diets containing 30% solvent-extracted grape seed oil meal had the same growth rate as calves fed a cereal-based diet. Up to 50% grape seed oil meal in the diet was possible without detrimental effects on health and carcass characteristics (Bayon, 1971). In Belgium, a series of trials concluded that 10% grape seed oil meal could be successfully incorporated in complete dry rations for fattening bulls, resulting in good performance and carcass characteristics. The feed value of grape seed oil meal 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).
Sheep
Grape seeds
Early trials found that whole grape seeds could be included in diets for lambs at up to 20% (Hogan et al., 1982) or 30% (Accardi et al., 1977). More recently, whole grape seed meal included in lamb diets at 10% of the diet produced weight gains and final live weights greater than those produced with the control feed. A 20% inclusion in the diet gave feed conversion indexes similar to those obtained using the control feed. Slaughter data, pH measurements, dissection data and chemical composition of the meat 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 atherogenicity 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 for the consumer, especially when they were 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 the 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, in lambs fed diets containing 40% grape seed oil meal there was 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 a correspondingly lower carcass yield (Mavrogenis et al., 1973).
