Walnut oil meal and kernels
Walnut oil meal and other oil-containing walnut products can readily turn rancid and become unpalatable to livestock (Göhl, 1982). It was observed in the 19th century that meat from animals fed rancid walnut oil meal was of poor quality and had an unpleasant texture and smell (Cornevin, 1892).
Leaves
Phenolic acids and flavonoids have been found in walnut leaves (Amaral et al., 2004). The total phenolic content in leaves ranged from 0.055 to 0.477 g/kg DM according to the variety and the season (Cosmolescu et al., 2011). Juglans regia leaves also contain progesterone (Pauli et al., 2010), which could cause reproductive problems in animals. However, this effect has not been demonstrated and walnut leaves are usually not fed to livestock.