This study determined the chemical composition and metabolizable energy (ME) value for ruminants of seeds and pulps from grape pomaces (GP), which were produced from white and red Vitis vinifera cultivars in Italy and California (USA). Six Italian (i.e., three white and three red) and five California red cultivars were collected after the crush of grape juice had been completed and were ensiled in micro-silos for 45 d. Fresh and ensiled samples were manually sieved to separate seeds from the pulp plus skin fraction and an overall inventory of 44 samples was obtained from the 24 Italian and 20 California samples (i.e., seeds and pulp fractions, fresh or ensiled from 6 or 5 cultivars, respectively). Both in seeds and pulp, the red Italian samples had higher organic matter (P<0.01), ether extract (P<0.05), neutral detergent fiber (aNDF, P<0.01), acid detergent fiber (ADF, P<0.01), lignin(sa, P<0.01) and Cu (P=0.02 and P<0.01, respectively) relative to the California red samples. In addition, K (P<0.01), Fe (P<0.01) and Zn (P=0.03 and P<0.01, respectively in seeds and pulps) were higher in red samples from California versus those from Italy. Italian white samples had higher saponins in pulp (SAP, P<0.05) and tended to have higher total extractable phenolics both in seeds and pulps (P=0.07 and P=0.10, respectively) than did Italian reds. Both in seeds and pulps, ensiling increased concentrations of aNDF (P<0.01 and P=0.08, respectively), ADF (P<0.01) and lignin(sa) (P<0.01 and P=0.03, respectively), had no impact on mineral levels and decreased concentrations anthocyanins (P=0.05) and SAP (P=0.01), respectively in seeds and pulp. Samples were fermented in diluted rumen fluid to measure in vitro rumen fermentability in terms of gas production, which was used to predict ME. Gas production from seeds of different origin were similar, with the exception of higher values at 48 h in red California cultivars with respect to those from Italy (19.2 ml versus 18.0 ml, P<0.05). In pulps, Italian reds did not differ from Italian whites, but had lower gas production than the red California samples (9.2 ml versus 12.2 ml, 16.6 ml versus 21.3 ml, 26.3 versus 32.7, P<0.01, at 4, 24 and 48 h respectively). Ensiling reduced gas production in seeds at 24 and 48 h of incubation (P<0.01) and in pulps at 48 h (P=0.09). Seeds from Italian red samples were lower (P<0.01) in ME than Italian whites (6.23 MJ/kg DM versus 6.89 MJ/kg DM, P<0.01) and higher (P<0.01) than the California samples (5.58 MJ/kg DM). There were no differences between ME of the groups of pulps, but ensiling reduced estimated ME content in seeds (5.94 MJ/kg DM versus 6.54 MJ/kg DM, P<0.01), but not in pulps. On the basis of our results, and in agreement with other recent papers and/or textbook data, the potential to use de-seeded GP as a feed in diets of high producing ruminants is limited
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