Browsers and grazers
27-10-2022
Vegetable material is relatively difficult to digest due to the presence of fiber-rich cell walls. Due to these cell walls, chewing and digesting plant material takes more energy. To break down these cell walls and release energy, herbivores depend on certain bacteria during the fermentation process. In addition, the nutritional value of plant material is much lower than that of animal products, so that the food intake of many herbivores is higher than that of carnivores and omnivores.
Differences between browse and grasses
There are major differences between the plant material eaten by herbivores. The main differences are between the categories: grasses and browse (see table). First of all, grasses consist of thicker, slow-digesting fibers (cellulose) and weeds consist of thin, fast-digesting fibers. In contrast, browse often contains more indigestible fibers of lignin. The thickness and amount of indigestible fibers depend on the season, so that the nutritional value of browse fluctuates more strongly. In contrast, grasses are more stable throughout the year. Secondly, there is a difference between the protection mechanisms of grasses and browse. For example, grasses have more silica, which causes teeth to wear off; and browse more tannins, which reduce digestibility. Thirdly, there is a difference between the way of growing, which makes grasses a more stable form of food for large herbivores, while browse brings more diversity in the diet.
Source: (Shipley, 1999)
Classification of browsers and grazers
Different herbivores use different plant parts. According to Hofmann and Stewart (1972) there are three groups: 1) Grazers, where <25% of the diet is browse; 2) Browsers, where >75% is browse; or 3) Intermediates, who select both grasses and browse. Eating different plant parts allows many different species of herbivores to live in the same place without directly competing with each other for food. According to Hofmann (1989), herbivores can be classified as 25% grazers, 40% browsers, and 35% intermediates. The table below shows an example of such a layout. In which group an animal is classified is partly on a subjective basis and therefore not black and white.
Source: (Hofmann, 1989)
Difference in digestion between browsers and grazers
The digestive systems of browsers and grazers are specialized to digest the food from their preferred diet as well as possible. Grazers benefit from teeth with a high crown, short roots and extra enamel due to rapid tooth wear from fibrous and silica-rich material. In contrast, browsers have shorter crowns and longer tooth roots. The shape of the muzzle also differs between the two; grazers often have a larger snout so that more material can be eaten, but this means that they are less able to graze selectively. Browsers have a narrower snout, longer tongue and relatively larger mouth opening. With this, food can be properly selected by, for example, stripping leaves from a branch.
Management
In order to provide all herbivores with a good diet, it is important to know which category they belong to. In general, fruit is not recommended and a salt stone is recommended. Furthermore, grazers can be fed with different types of hay and possibly a small amount of browse. Browsers can be fed with different browser variants and additionally with some roughage (such as alfalfa). Intermediates can be fed with both hays and browses, with a ratio of 50:50 recommended. Both hay types and browse varieties can be fed dry and fresh in combination.
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