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basslerChickens on Grassland - Who Gains?

Arnd Bassler
Department of Animal Nutrition and Management
The Swedish University of Agricultural Sciences
June 2002


I am working with broiler production in organic agriculture. In conventional agriculture, broilers are kept indoors all the time. "Organic" implies that the broilers have to be raised on grassland. I investigate how this affects the broilers' nutrition, health - and the land they are kept on. Today, organic broiler production is quite uncommon. But increasing environmental and animal welfare concerns give it a potential for the future. I try to improve broiler production on grassland. My investigation might provide arguments in favor of this way of raising broilers but also help to face its limitations.


Given access to grassland, broilers are instinctively searching the land for food. They move around and scratch and in this way get gymnastic exercises, but also affect the grassland's growth and condition. My research project has to do with the interaction between chickens and grassland.

I focus on three questions:


1. The broilers find some extra feed on the grass range. But is that a relevant contribution to their feed ration? Broilers cannot eat much herbage. Their digestive system is different from that of cattle, sheep or horses. However, they have the ability to "pick" out the youngest grass and clover leaves, which are highest in energy and protein. In addition they "hunt" earthworms and insects which are even more nutritious for them. In an experiment I compared broilers raised on grassland with broilers raised under the same conditions - including amount of given feed - but outdoors on straw. I found the grassland broilers to be some five percent heavier at slaughter day. I conclude that this difference is due to extra feed intake from grassland. In a second experiment, I will again keep the birds on grassland compared with outdoors on straw but use a different method:


Instead of feeding them with a balanced feed, the broilers are simultaneously offered single feed components like wheat (high in energy) or fishmeal (high in protein) and may freely choose among them according to their appetite. I assume here that the birds are "wise enough" to compose their diet according to their needs. By then comparing the self-selected diets of the groups on grassland and straw, I will get a more detailed picture of the nutrients the broilers find on the grassland.


2. Physical exercise is known to strengthen bones. Does grassland sufficiently stimulate physical activity to achieve that?
Modern broiler breeds often have too weak legs, which is an unwanted side effect of fast growth: The muscles (i.e. meat) grow faster than other organs. This can lead to a deformation of the bones and make movements painful. I want to find out, whether access to grassland stimulates physical activity and improves leg health. Again I compare broilers on grassland and outdoors on straw, but here in addition also indoors on wood shavings, since this is the environment most broilers are raised in. I do behavioral observations, paying special attention to the behavior that includes leg activity, like running or scratching the ground. In addition to the behavioral studies, I do a scoring of the leg health of the living birds with the help of a veterinarian: Using a method called "gait scoring", I judge how the individual broiler walks. Abnormalities are regarded as symptoms of leg problems.


3. Do broilers benefit or wear out the grassland they are kept on?

The grasslands' herbage production often is used first of all by cattle. Broilers can consume only a small part of the grass that grows on the land they are kept on. A farmer, who wants to combine cattle and broilers therefore needs to know what impact the broilers have on the grassland: Does their selective grazing affect the growth of the grass and clover or is it negligible? And what is the effect of scratching and manure on the grassland? All factors might also work together, enhancing or compensating one another. I cut grassland samples before and after the broilers have been on the land and parallel samples where no broilers have been at all. The samples are analyzed for grass and clover content and overall yield.

The results of my research will support the decision making of farmers who consider to keep broilers on grassland or are already doing this and want to improve their system. It finally might also have influence on the rules that are applied in organic agriculture.