Not exactly conservation and environment, tho somewhat related - and related to H5N1 and wild birds, as well as SARS (which evidently originated in farms with civet cats, in China). Article in the Guardian tells of factory farming, especially poultry. Includes:
In its Animal Welfare Guidelines, the US National Chicken Council indicates an appropriate stocking density to be eight-tenths of a square foot per bird. Try to picture it. Find a piece of printer paper and imagine a full-grown bird shaped something like a football with legs standing on it. Imagine 25,000 of these rectangles in a grid. Now enclose the grid with windowless walls and put a ceiling on top. Run in automated (drug-laced) feed, water, heating, and ventilation systems. This is a farm.
Now to the farming. First, find a chicken that will grow big fast on as little feed as possible. The muscles and fat tissues of the newly engineered broiler birds – chickens that become meat, as opposed to layers, chickens that lay eggs – grow significantly faster than their bones, leading to deformities and disease. Somewhere between 1% and 4% of the birds will die writhing in convulsions from sudden-death syndrome, a condition virtually unknown outside of factory farms. Three out of four will have some degree of walking impairment, and common sense suggests they are in chronic pain.
For broilers, leave the lights on about 24 hours a day for the first week or so of the chicks' lives. This encourages them to eat more.
Air-chilling reduces the weight of a bird's carcass, but water-chilling causes a dead bird to soak up water (the "faecal soup"). One study has shown that simply placing the chicken carcasses in sealed plastic bags during the chilling stage would eliminate cross-contamination. But that would also eliminate an opportunity to turn waste-water into tens of millions of dollars' worth of additional weight in poultry products.
What I've described is not exceptional. It isn't the result of masochistic workers, defective machinery, or "bad apples". It is the rule. More than 99% of all chickens sold for meat in America live and die like this. For each food species, animal agriculture is now dominated by the factory farm – 97% of laying hens, 99% of turkeys, 95% of pigs and 78% of cattle.
Today six billion chickens are raised in roughly these conditions each year in the EU, over nine billion in America, and more than seven billion in China. All told, there are 50 billion factory-farmed birds worldwide. Every year 50 billion birds are made to live and die like this.