Written by: Dr. Jacquie Jacob, University of Kentucky
Free-range chickens eat low to moderate levels of forage, or crops in a pasture. Currently, researchers do not have a clear understanding of the effects of forage intake. To begin with, variation exists related to pasture systems in which chickens feed. The amount and type of outdoor access varies depending on the management system; the quality of the pasture used varies; and the same pasture can produce different results in different seasons. Moreover, the nutritional value of forage as well as the effects of forage intake on microbial contamination of poultry and quality of poultry products are not clear.
The nutritional value of the forage and insects consumed by chickens that have outdoor access remains unclear. Some researchers have reported decreased carcass yield and only marginal effects on vitamin E and cholesterol content of meat from pasture-raised chickens. Others have documented increased vitamin E and alpha-linolenic acid contents and decreased cholesterol content in meat from pasture-raised chickens.
Fiber is another factor that can be affected by allowing chickens to free-range or feed on pasture. Fiber is an indigestible carbohydrate (compound made up of carbon, hydrogen, and oxygen). It is the part of plant foods that the body cannot digest or absorb. The two types of fiber are soluble fiber and insoluble fiber. Soluble fiber increases the viscosity and reduces the flow rate of the digestive gut contents, thereby decreasing digestion efficiency. Insoluble fiber, on the other hand, acts as bulking agent and has been shown to increase the rate of passage of digestive gut contents. Traditionally, dietary fiber has been considered to dilute the nutrient content of diets and is often classified as an antinutritional factor. However, moderate amounts of fiber have been shown to be beneficial. For example, fiber has been shown to increase the gut immune system and encourage growth of beneficial bacteria. Also, diets high in insoluble fiber are effective in reducing cannibalism in poultry flocks.
The diet of chickens that free-range or feed on pasture can be supplemented with dietary fiber. Dietary fiber has been shown to increase the nutrient availability of different feedstuffs, including wheat, oats, and soybean meal. Examples of high-fiber ingredients commonly used in poultry diets include alfalfa, brewer's spent grains, rice bran, and wheat middlings. Most feed labels indicate a maximum of dietary fiber in the product, and some producers believe labels should state the minimum level of dietary fiber in the product as well.
The response to dietary fiber depends on the source and level of dietary fiber and on other ingredients in the diet. Moderate levels (2 to 3 percent) of insoluble fiber, such as oat hulls, usually improves growth performance of broilers. Dietary fiber had no beneficial effect while raising replacement pullets, and there was no effect on subsequent laying house performance. However, dietary fiber has been shown to reduce total manure ammonia emission of a laying house.
Whether eating forage or prepared feeds, poultry are constantly exposed to a wide variety of microbes. Although some of these microbes can cause disease, few chickens succumb to infection due to the innate immune system. For example, Salmonella species and Campylobacter commonly inhabit the digestive tract of food animals without those animals exhibiting any obvious clinical signs. (These bacteria, however, are excreted in the feces and can contaminate the carcasses of meat poultry, such as chickens and turkeys.) There may be ways to further protect chickens from disease-causing microbes. Researchers have looked at feed ingredients as a way to stimulate the innate immune system. Such ingredients are referred to as bioactive food components. For example, using alfalfa in an induced molting program results in chickens having a more functional immune response than those molted by feed withdrawal. The immune response was comparable to that of fully fed hens.
Research regarding comparison of meat attributes for poultry raised in different systems has produced varied results. Some taste panels have preferred the meat from grazing animals, whereas other taste panels could not detect any differences.