Different animals select, bite off, and chew plants differently. Each animal type has a tool or set of tools that help them gather food (prehension), grind it (mastication), and swallow (deglutition). Pigs use their snout to get the process started. Poultry scoop up food bits. This section discusses the main livestock involved in forage production, beef and dairy cows, horses, sheep, and goats. Forage-livestock managers should consider the differences in livestock chewing in establishing grazing programs.
Equipped with a long and dexterous tongue, the cow can wrap its tongue around plant parts and pull the food into its mouth where it is placed between its lower jaw and a pad on the upper surface. Once in the mouth, the cow swings its head to severe the plant parts and chews the food slightly, and mixes it with saliva before swallowing. Later the cow will regurgitate the food to chew and grind it again. This process is called rumination or chewing the cud. The actual chewing portion of a cow's day consumes eight hours and ruminating takes about 12 hours. Cows can take around 890 bites per hour for about 8 hours a day. Due to the design of the cow's lips, teeth, and jaw a cow can't easily get closer than 2 inches from the soil. An ideal height of grass is about 6 inches, higher or lower than that will consume more time and energy for the cow. Cows will not graze much longer than 8 hours, so grass at the proper height will increase intake and improve animal nutrition. Cows also prefer not to eat around their own paddies but are willing to graze after a different type of animal has defecated. Cows like to graze on rolling land, although they are able to graze anywhere.
A horse will eat more often than a ruminant animal because it doesn't spend time ruminating, but it will eat a smaller amount per session because its stomach is smaller on a per body weight basis. Horses have upper and lower sets of front incisor teeth used primarily for biting while the back set of molars are used mainly for grinding food. A strong, sensitive, upper lip gathers the food and brings it to the incisors. Its short tongue is less essential to the eating process. The upper teeth are wider which causes wear on the teeth from grinding and sometimes there is a need for their teeth to be filed. Horses can graze a pasture to the soil level because the teeth and head can get so close to the sod. They tend to section off their pastures into eating and spoiling areas.
While cows may best utilize their tongue, sheep use their lips and teeth as their primary forage gathering tools. Cleft lips move away from their teeth on the lower jaw and help bring food in, while the upper jaw has a dental pad that is about 1.6 inches wide. Together, the teeth on the lower jaw and the pad on the upper jaw sever the leaf blades. Such a mouth structure allows sheep to bite closer to the ground than cows and the ability to be more selective. The ideal grass height for sheep is about 4 inches.
Both cows and sheep are ruminant animals which mean they have four stomachs through which they cycle feed. This requires time for rumination or the regurgitation of the bolus that was made from bites of forage and rechewing, preparing for easier digestion. So, cows and sheep need time for both eating and ruminating. Maximum efficiency is achieved by providing abundant forage at an optimal height.
Much like sheep, goats also have teeth on their lower jaw and a strong dental pad on their upper lip. The upper lip is incredibly mobile and with the help of a strong tongue, goats can selectively grab and are able to avoid thorns and spines. Goats select woodier browse and will choose young, tender leaves and twigs, before grasses and legumes. Thus, young trees will need to be protected in agroforestry systems.