Compost is a mixture of plant materials that contain carbon or nitrogen. Carbon sources include dead leaves, sawdust, and shredded paper. Nitrogen can be found in grass clippings, salad waste and trimmings, and manures from herbivorous animals. Manures from carnivorous animals, such as dogs and cats, should not be used in home compost piles.
Depending on the diets and digestive systems of different animal species, the quality and nitrogen content of manures used for composting may vary. Understanding these factors will allow you to choose the best manure for the compost you want to make. The manures most commonly available are horse, cow, pig, chicken, and rabbit. While all are very useful in compost piles, each can have advantages and disadvantages.
Horse manure comes from stables, and is usually mixed with the straw or wood shavings that were used as bedding for the animals. Although it is moderately high in nitrogen, some of that nitrogen will get used up by the chemical and biological breakdown of the bedding materials.
Horse manure often contains weed seeds from plants the animal ate, which can pass intact and still viable through its digestive system. Thorough hot composting will kill some of those weed seeds, many are likely to remain. Even so, its wide availability makes horse manure a valuable addition to the compost pile.
Cow and Pig Manures
While cows eat many of the same plants eaten by horses, weed seeds do not survive in a cow's digestive system. Cattle (along with goats, sheep, deer, and some other animals) are ruminants that have a system of two stomachs to double-digest their food. Cattle manure is often collected as a slurry, does not have bedding materials mixed in with it, and will break down easily. For these reasons, cow manure is better than horse manure in a compost pile. Nitrogen level is lower than that for horse manure.
Pig (hog) manure is collected as a slurry. Its high odor level will diminish when it is combined with dry carboniferous materials. Its nitrogen and other nutrient levels are similar to cow manure.
Chicken manure has long been a favorite of gardeners. Its high nitrogen content makes it ideal to "fire up" a compost pile that has a lot of carbon, but it also means that it should not be added to the soil directly around plants---it may burn the roots. The strong ammonia smell of chicken manure almost disappears when it is mixed with carboniferous materials such as dead leaves. As a general rule, it is best to compost chicken manure rather than add it directly to the soil.
Rabbit manure is not as widely available as horse, cow, or chicken manures, but its high nitrogen level and phosphorus content makes it worth seeking. It is almost odorless, and the small pellets break down easily.
Many people who have a worm farm (vermicompost) use rabbit manure mixed with other materials, such as shredded newspaper, to feed the worms. Rabbit manure can also be used to make high quality compost tea.
The nutrient content and nitrogen level of animal manures varies with the species, the age and condition of the animal, the time of year, and manure storage conditions. However, when properly composted all herbivorous animal manures are a valuable addition to the compost pile. When the finished compost is added to your garden soil, it will increase its organic content, and improve its nutrient- and water-holding ability.