Grazers

Digestion Caecal System: Rumen System: The horse has this type of digestive system Rumen System: "Ruminants" include the wild ungulates, cattle, goats, and sheep. For wild ungulates, the type of digestive system they possess controls food selection. Among ungulates there are two types of digestive systems rumen system and ceacal system. Both systems enable ungulates to digest large plant carbohydrates such as cellulose, using microbial fermentation. While both systems use similar fermentation processes, the sites of the actual fermentation process differ. This difference can have important management implications for maintaining sustainable forage bases. Rumen System: "Ruminants" include the wild ungulates, cattle, goats, and sheep. Caecal System: The horse has this type of digestive system. Rumen system Fermintation process occurs before the stomach in an area called the rumen. When roughage is eaten, it is chewed on, soaked with saliva, and then swallowed. This bolus of food is called “the cud”. It continues down to the rumen to be digested by micro-organisms in a fermintation process. At regular intervals the cud is brought back up to be chewed on some more to break down large particles and create greater surface areas for the microbes to work on. Then it is swallowed again. This entire process is called rumination. Caecal system Fermintation process occurs after the stomach in a large pouch called the caecum (an enlarged pouch of the large intestine).

Comparison The ruminant advantages The caecal advantages Longer food retention time Fermentation – protein source The caecal advantages Shorter food retention time – greater amount of material at lower quality Two sets of teeth The ruminant has two advantages over the caecal digester: More digestion of cellulose - Ruminants have longer food retention time and larger digestive surface area due to regurgitation and re-chewing. As a result, there is greater digestion of the cellulose in ruminants. Added source of protein - Ruminants have the fermentation (digestion) chamber before the stomach. This allows for the digestion of dead microbe bodies from the fermentation process. Digested protein from the dead microbes bodies becomes an important source of protein for these ungulates. The caecal digester has two advantages over the ruminant: Lower quality diet - Food spends less time in the caecal digestive track. As a reult, they can process a much greater amount of material. This means they can exist on a much lower quality diet than the ruminants. Horses have two sets of teeth rather than just the lowers possessed by cattle and wild ungulates. This allows for shearing of plants much closer to the ground.

Three Types of Ruminants Selective feeders/Browsers Roughage feeders/Grazers Intermediate feeders/Mixed forages There are three types of ruminants: Selective feeders/Browsers - feed on forbs and shrubs. With the exception of domestic goats they do not do well on mature grass, although they will consume green grass if shrubs and forbs are not available. In addition to the domestic goat, browsers include moose, pronghorn antelope, mule deer, and white tail deer. Roughage feeders/Grazers - feed predominantly on grasses. Grazers include cattle, elk, bighorn sheep, mountain goats, musk oxen and bison. Intermediate feeders/Mixed foragers - have the greatest ability to adjust their feeding habits to whatever forage is available. Domestic sheep are the most adaptable domestic ungulate and will use whatever forage is available. Burros and caribou are also considered to be intermediate feeders. Table 1 shows the forage selection by various herbivores.

What are forbs? Non-wooded, broad leaved plant other than grass Weed "Most weeds are forbs, but all forbs are not necessarily weeds.“ A forb is a non-wooded, broad leaved plant other than grass, especially one growing in a field, prairie, or meadow. A more common term for them is "weed". However, many forbs have significant food value for livestock as well as wildlife, and the animals may even prefer them to grasses. Some have greater protein content. Photo: Clockwise from top left: pale purple coneflower, ashy sunflower, white clover, wild carrot.

What are Shrubs? Woody plant less than 15 feet high, either: without a distinct main stem, or with branches persisting on the main stem almost to its base. A shrub is a woody plant less than 5 meters (approx. 15 feet) high, either without a distinct main stem, or with branches persisting on the main stem almost to its base. Shrubs serve as habitat and food for many wildlife species. Flowers provide nectar for bees, butterflies and hummingbirds. Berries provide food for songbirds, upland game birds, and mammals. Leaves, twigs, and buds provide food, shelter and nesting habitat. Photo: Clockwise from top left: chokecherry, service berry, russian olive, huckleberry.

Forage Selection

Seasonal Trends Food choice dependent upon: Spring, Summer, Early Fall Availability Time of Year Palatability Spring, Summer, Early Fall Wild ungulates – soluble carbohydrates Winter Trees and shrubs The type of forage selected is also dependent on the availability of the food source and the time of year, and palatability at that time. Each plant species has a different nutrient content at different times of the year. Early in the season the amounts of digestible carbohydrates, proteins, and vitamins are the greatest and fibre content is lower. As the season progresses the amount of fiber increases while the others decrease.   Spring Summer Early Fall: Wild ungulates tend to consume a greater amount of soluble carbohydrate (found in rapidly growing portions of plants) and cellulose during spring, summer and early fall. This allows for accumulation of energy stored as fat, which will be utilized during the winter. Winter: The diet changes to trees and shrubs in winter since they are a better source of protein at that time. This allows for the maintenance of muscle mass. In addition, the female needs protein to maintain gestation during the winter and to produce milk for the young in the spring. For successful reproduction, protein in sufficient amounts is required through this time. Shrubs maintain a greater amount of protein and carotene throughout the winter. This percent difference is great enough to maintain muscle mass, gestation and lactation. The grasses and forbs do not maintain the minimum percent protein and carotene needed. This seasonal difference in nutrient and fiber composition is reflected in the percentage of grasses, forbs and shrubs eaten in different seasons. Table 2 illustrates this point.

Seasonal Changes

Density and Mix of Animals Density – how well animals co-exist Type of animal mixture Deer with sheet, goats, and cattle Antelope and cattle Because of the digestive system requirements (and limitations) - the density and mix of livestock and wildlife animals determines how well they co-exist. For example, it has been shown that as livestock stocking rates increase, the number of white-tailed deer decreases (Merrill et al. 1957; McMahan 1964; Readon et al. 1978). However, the decline in deer numbers is dependent upon the type of livestock animals. Deer numbers decline more in pastures with sheep and goats than those stocked with cattle. This can be attributed to the fact that the dietary overlap with sheep, goats, and white-tailed deer is much greater than with cattle and deer. Deer are browsers, cattle are grazers - and therefore, they are not competing for the same food source (Bryant et al. 1979; Blankenship et al. 1985). Photo: Antelope are primarily browsers and cattle are primarily grazers.