Stocking density is a farming term that refers to the relationship between the number of livestock and the size of the space within which they are kept. Low stocking rates in livestock – in this case, chickens – may result in inefficient production for farmers and loss of profits. However, studies have shown changes in behavior, production capability and mortality rates when the density rates are too high. Animal welfare advocates also promote lower stocking density due to the stress that crowded conditions can cause for birds.
Broiler Chickens
When raising meat birds in an industrial environment, a Danish study correlated higher stocking densities with poorer leg health. Since this made it painful for the birds to walk, they were less able to access food and therefore ended up at a lighter weight than the control group of less-crowded birds. A Japanese study showed that high stocking density increased chicken mortality in the winter and summer seasons, as well as lowered summertime body weights. This suggests that not only does reducing stocking density increase animal welfare, but it also improves the production value for farmers.
Higher stocking densities can also result in housing issues that can affect the health of chickens. If ventilation is poor, ammonia levels can become dangerous. Chickens may be unable to access feed and water as effectively, and both temperature and humidity may rise to unhealthy levels. A study at the University of Oxford suggested that the birds’ mortality rates improved in companies that used litter to reduce moisture and improved ventilation to reduce ammonia. However, the study also acknowledged that stocking density affected animal welfare in more ways than mortality rates.
Egg Layers
Laying hens are also affected by high stocking density in caged environments. In multiple studies, high stocking density was correlated with lower egg production and lower egg weight. One study in “Tropical Animal Health and Production” (2021) found that hens raised with lower stocking density and high light levels reached maturity before other tested groups. This same study showed that hens at high stocking density had poorer feed ratios. A California study showed that birds in low stocking density environments had fewer feathers broken or missing than those birds raised in a more crowded environment.
Interestingly, few studies could be found on density in outdoor environments. One research article from Australia in 2017 showed little difference in birds raised in high or low stocking density environments. Egg production and quality were similar in all groups. However, it was noted that birds in the low-density groups were more likely to use the provided outdoor range compared to those in more densely populated groups. This suggests a possible difference in the nutritional quality of the eggs.
Effects on the Young
The effects of high-density conditions can also be seen in chicks and pullets. The University of Hohenheim in Germany tested birds by varying the stocking density until seven weeks of age, and then keeping all birds in areas of 2.4 birds/m2 until twenty-eight weeks of age. Despite having a comparable environment as adults, the birds raised in crowded areas as chicks displayed more pecking behaviors, poorer physical condition and poorer health as adults.
It is important to note that other studies have shown that non-brooded chicks – those without a hen to care for them – show higher levels of these behaviors compared to those raised by a broody hen. These are common behaviors when the chicks are given stocking densities of those commonly used in industrial chicken raising. However, a Danish study in 2015 showed that dark brooders can mitigate some of these anti-social behaviors. This suggests that either density is not entirely responsible for these behaviors, or that the effects may be mitigated by other factors.
This article about stocking density was written for Chickens magazine. Click here to subscribe.
