Because he’s too fat. Broiler chickens (the ones raised for meat) are essentially a cash crop, grown much like wheat or corn. When the chicken is ripe it’s harvested. The Grim Reaper. We admit to not knowing much about poultry science and the business it supports, but because of our interest in bird flu we have been learning. There is a some well founded suspicion intensive poultry farming is one of the enabling conditions for the evolution and spread of bird flu.
These birds are raised under very difficult conditions and lead their short lives in extraordinary population densities, often more than a hundred pounds of birds per square meter. I’m not sure how many birds this represents but modern methods of poultry husbandry have greatly accelerated chicken growth rates, which have increased 300% since the middle of the last century. These birds used to gain about 25 grams (just under an ounce) a day. They now gain about 4 ounces a day (100 grams). And with that growth comes “leg disorders.” Translation: they can’t walk. A very large survey of leg disorders in commercially raised broilers has just been published in PLoS ONE, an open access journal. You can read it here. Here’s the gist.
A team of veterinarians in the UK assessed the ability of 51,00 birds to walk, using a standardized gait scoring method. The birds were in flocks from five different companies, representing an estimated 4.8 million birds in 176 different flocks ( about half the UK’s productive capacity). In addition information was obtained from the companies on 150 management practices in an effort to see if any were significantly associated with poor leg health. These practices are used throughout the global industry of industrial poultry farming.
Over a quarter of the birds had significant difficulty walking and over 3% couldn’t walk at all at 40 weeks, a typical age at slaughter. The paper includes (at the end) download links to short movies illustrating each of the six gait categories (warning: clicking these links will download a .mov file of sizes 2 and 5 MB respectively; 0 is normal [2.19 MB], 5 is unable to walk [5.71 MB]). There was also considerable variation in the flock gait scores in different companies. Some were much better than others.
But many factors were associated with gait score besides company. First was season. The lowest (i.e., best) gait scores were in March, the highest (worst) in September. It is interesting to note this puts gait score roughly in phase with influenza seasonality. They are probably not related but the reason for the seasonality is unclear. The older the bird the worse the gait score. Interestingly bird genotype was also a factor. Commercial poultry are of roughly two genetic stocks, representing two different international breeding companies that supply most of them. Most flocks have both genetic stocks, but the higher the percentage of the genotype the authors labeled “A” the worse the average flock gait. Increase in wheat in the diet was also associated with better gait. Poultry food is pelletized to reduce wastage but some of it is poorly pelletized and becomes powdery. Poorly pelletized food is also associated with better gait. The reason in both instance is probably the same: the birds don’t grow as fast. Birds also don’t feed in the dark, so the length of darkness in the sheds (many are lit 24 hours a day) also correlated with better gait.
Two other management practices deserve mention. One is the use of antibiotics. Antibiotics are routinely used in all poultry operations. This routine use couldn’t be studied because “variables have to vary.” But some companies use extra antibiotics and this seems to improve locomotion, presumably (so the companies believe) because the birds are healthier. The other major factor affecting bird welfare as measured by the ability to walk is stocking density, densities which are shockingly high. Whether the effect on locomotion is merely that the birds can’t move around or because of the huge accumulation of their own waste they live in is unclear. But it is no real surprise, whatever the explanation.
These birds are raised to maximize profit, not maximize animal welfare. That much is obvious. But it doesn’t mean that animal welfare considerations are irrelevant, even from the purely commercial point of view:
The study indicates that modern husbandry and genotypes, biased towards economics of production, have been detrimental to poultry welfare in compromising the ability of chickens to walk. However, we demonstrate that within the current framework there is variation in the magnitude of the problem between different flocks, and so some scope to improve walking ability through alterations in husbandry practice. Work needs to be carried out on the predictability of these risks, and the economics of improved welfare practices, for them to gain industry acceptance. An informed balance could then be drawn between profitability and our moral obligation to maintain good standards of animal welfare. The agreement, in May 2007, within the EU of new regulations governing the conditions under which broilers may be reared is a recognition of the problems associated with modern broiler production and is an attempt at a first step towards remedying the situation.
Research shows that consumers currently know little about how broiler chickens are reared but can be shocked when presented with information about current commercial practices. Since the sustainability of intensive broiler production depends on continued consumer acceptance of the farming practices involved, the broiler industry will need to work with the scientific community to develop more robust and healthier genotypes and to ensure that optimal husbandry and management practices are fully implemented. (my emphasis; cites omitted; Knowles TG, Kestin SC, Haslam SM, Brown SN, Green LE, et al. (2008) Leg Disorders in Broiler Chickens: Prevalence, Risk Factors and Prevention. PLoS ONE 3(2): e1545. doi:10.1371/journal.pone.0001545).
So here’s the question: Leg or breast?