Cage or battery farms supply 89% of eggs in New Zealand. A cage is usually just over half a square metre, while so-called enriched cages are larger and have a perch, nest box and dust bath. Cage floors are made of mesh and are gently sloped, allowing the eggs to roll out. Eggs are collected by hand or in an automated system by conveyor belt. Feed is available from a trough in front of the cage, and water from dispensers. Manure drops through the mesh floor of the cage, and in automated systems is carried away by conveyor belt.
Even in the early days of the poultry industry, hen housing was a matter for debate. An article in the 1910 issue of the Journal of Agriculture stated that ‘The proper housing of fowls is one of the most discussed questions of the day. … The old, closed in and ill ventilated house must go. The open front and draught proof structure is the ideal’. 1
Free-range farms supply 9.7% of eggs in New Zealand. The typical, medium-sized farm has 5,000–10,000 birds, while small farms can have as few as 3,000 hens and larger operations up to 60,000. The birds move freely inside a shed, which is fitted with nest boxes and perches. Pop-holes provide access to an outdoor area called the range, although it is not known whether all the hens spend time there.
Barn production systems supply 1.4% of eggs. The birds live inside a shed fitted with nest boxes and perches, but never go outside.
Out, damned spot
Occasionally you might find a blood spot on a yolk. They are caused during the egg’s formation by a ruptured blood vessel on the yolk’s surface. Less than 1% of eggs sold have blood spots, as they are normally removed during quality checking. You can eat the egg as usual, or remove the spot.
After the eggs have been collected, they are examined for quality. In a process called candling, a bright light is shone through the egg to show up defects. Dirty, cracked or thin-shelled ones are removed. Those with cracks – about 15% – are processed into liquid or dried form, and used in commercial baking and cooking.
Whole eggs that have been approved by candling are graded for packing. The minimum size for gradings are 35 grams for a pullet (size 4), 44 grams for a medium (size 5), 53 grams for a standard (size 6), 62 grams for a large (size 7), and 68 grams for a jumbo (size 8). Mixed-grade eggs vary in size.
Double-yolked eggs are sometimes produced by birds when they first start laying. They are caused when the bird’s ovaries release two yolks at once which grow together within a single shell. Eggs with two yolks are often larger, although sometimes they are small but heavy for their size. About one in every 1,000 eggs has two yolks.
Shell and yolk colour
Eggshell colour varies from white to caramel-brown. There is no difference in quality or taste between eggs of different colours. Shell colour is genetically determined – breeds derived from the Rhode Island Red (such as the Shaver Brown and Hyline Brown) produce brown eggs, while those from the Leghorn (such as the Shaver White and Hyline White) produce white eggs. The colour of a hen’s eggs can be determined by examining her feathers and ear lobes – hens with red feathers and ear lobes produce brown eggs, while those with white feathers and ear lobes produce white eggs. New Zealand customers tend to prefer brown eggs, which in 2009 made up 95% of eggs.
What’s in a yolk?
The yolk makes up a third of the liquid weight of an egg. It contains all of the fat and just under half the protein. All of the egg's zinc and vitamins A, D and E are in the yolk, which also contains more phosphorus, manganese, iron, iodine, copper, and calcium than the white. Yolk colour depends on the hen’s diet – hens fed corn produce the golden yolks preferred by most New Zealanders, while those fed wheat or barley lay paler yolks.
In the 2000s a wider range of eggs has become available, including organic, omega-3-enriched, and those produced by hens given whole-grain or vegetarian feed.
The welfare of laying hens is guided by the Animal Welfare (Layer Hen) Code of Welfare 2005, which was created by the National Animal Welfare Advisory Committee, a ministerial committee made up of animal-welfare experts and advisors.