In an industrial egg-producing facility, about half of the chicks will be male and would grow up to be roosters, which do not lay eggs and therefore provide no incentive for the breeder to preserve. Most of the male chicks are usually killed shortly after being sexed.

A typical cage is about the size of a filing cabinet drawer and holds eight to 10 hens.

The young piglets stay with their mothers for two to three weeks, after which their teeth are clipped, tails cut and the males are castrated – all without anaesthetic, according to the Canadian Coalition for Farm Animals. "The piglets are taken away to be fattened in nursery pens on concrete floors, then to “grower” pens, and finally to “finisher” pens until they reach slaughter weight of 250 pounds at six months old," the CCFA adds.

The CCFA says pigs may be legally transported in Canada without water, food or rest, for 36 hours. Photo: Pigs from Manitoba destined for Mexico died enroute in Texas after being left for days in a transport trailer without water in temperatures of over 90 degrees Farenheit.

The Canadian Coalition for Farm Animals estimates that 98 per cent of Canada's 26 million egg-laying hens are kept in small, crammed "battery cages." Pictured here is a feces-covered hen at an Ontario egg farm.

Each bird has less space than a sheet of notebook paper, according to the Canadian Coalition for Farm Animals.

Unlike free range hens pictured here, hens in cages are not able to perform natural behaviours such as nesting, perching, dust-bathing and stretching a wing or walking around.

Out of the 30 million pigs produced every year in Canada for slaughter, most are born to sows who are kept in two-feet-wide metal gestation crates, where they are unable to even turn around during their four-month pregnancy, says the Canadian Coalition for Farm Animals.

The European Union banned battery cages as of January 1, 2012. Photo: Former battery hens roost in the barn of their new home.

Early battery cages were often used for selecting hens based on performance since it is easy to track how many eggs each hen is laying if only one hen is placed in a cage. Later, this was combined with artificial insemination, giving a technique where each egg's parentage is known. This method is still used today.

The passage of California Proposition 2 in 2008 aimed to reduce or eliminate problems associated with battery cages. A standard for space relative to free movement and wingspan was set, rather than cage size.

Spatial restriction can lead to a wide range of abnormal behaviours, some of which are injurious to the hens or their cagemates.

Being indoors, hens in battery cages do not see sunlight. While there is no scientific evidence for this being a welfare problem, some animal advocates indicate it is a concern.

According to World's Poultry Science Journal, flocks are sometimes force molted, rather than being slaughtered, to reinvigorate egg-laying. This involves complete withdrawal of food (and sometimes water) for 7 to 14 days or sufficiently long to cause a body weight loss of 25 to 35%