grumpy // I understand that this is due to the belief that cows and hens do not give their milk or eggs voluntarily.//
Cows don't lactate unless they have given birth. The calves are taken off the mothers less than 24 hours after birth. Female ones are then fed powdered milk until weaning, male ones often killed or sold to Europe for the veal trade. Dairy is one of the most heartbreaking forms of farming, for something only humans seem to consume, the milk of another mammal.
Hens, well this is another story. Vegans cannot understand that hens will lay eggs even if they are nowhere near a cockerill. They will sit on those eggs if they are not collected until the eggs go rotten. The only cruel thing about eggs was when they were produced in battery cages which are now illegal, thanks in part to the huge campaign by Compassion in World Farming.