Ethanol
Ethanol is the main fermentation end product in apple pomace silage, with reported ethanol content as high as 17% of DM. It had thus been recommended to limit the quantities of pomace fed to livestock, or to feed it for relatively short periods (Alibes et al., 1984). In a silage made of whole, crushed apples, the ethanol level reached 22-29% of DM, which may have been caused by yeast alcoholic fermentation. It was impossible to decrease the pH, and the silage could not reach a stable state: it was, therefore, recommended to add a dry and fibrous material such as straw up to 30% of the DM (Rodrigues et al., 2008).
Pesticide residue
Culled apples and apple pomace include the skin, which retains a substantial proportion of the residues of lipophilic pesticides (Amvrazi, 2012). Ingested pesticides can be stored in fat tissues (Rumsey et al., 1977) and in milk, although at low levels (Chase et al., 1987). Hundreds of pesticides are registered and in use for apple production all over the world (up to 799 in the USA) (Drogué et al., 2012), and pesticide residues have been reported in several recent studies (Lozowicka et al., 2015; Pogăcean et al., 2014; Likudis et al., 2014; Szpyrka et al., 2013; Jardim et al., 2012; Latif et al., 2011). Although in most cases the contents of residues were below the Maximum Residue Levels established by local regulation, some have been found beyond this threshold. Residues observed on fresh fruits may not be present at the same level after fruit processing, because fruits are washed and brushed before being pressed. If apple pomace is to be used in ruminant feeding it must be verified that the level of pesticide residue is low. According to the Codex Alimentarius, the Maximum Residue Levels in dry apple pomace are 0.3 mg/kg for Fenarimol, 40 mg/kg for Fenbutatin Oxide, 120 mg/kg for Permethrin and 80 mg/kg for Propargite (Codex Alimentarius, 2003).
Choking
Like other fruits, apples can be dangerous to cattle and sheep when swallowed whole, as they may lodge in the oesophagus, causing obstruction. Cattle grazing in apple orchards are at risk as they are fond of picking apples hanging from the lowest branches (Tran, personal communication).