When grazing, ruminants swallow their food rapidly, sending large amounts into the largest chamber of the stomach, the rumen, where it is stored and partly digested before regurgitation and chewing when the animal is resting. Rumination is an adaption by which herbivores can spend as little time as possible feeding when they are most vulnerable to predation and then later digest their food in safer surroundings.
Muscular contractions of the stomach move food back and forth between the rumen and the second stomach chamber, the reticulum, which is often called the honeycomb due to the complex appearance of its inner lining. Bacteria and microorganisms in the rumen which can digest cellulose begin the digestion of the plant fibers. Fine fibers are broken down, so providing protein, vitamins, and organic acids which are then absorbed into the bloodstream of the animal. Coarser plant fibers are passed from the rumen to the reticulum, where further bacterial fermentation takes place, and the food is formed into soft chunks called the cud.
The cud is regurgitated and ground thoroughly between the molars with an almost circular motion of the lower jaw.
As ruminants develop, the reticulorumen and omasum grow rapidly and account for increasing proportions of the total stomach area. In mature cattle, the abomasum encompasses only 21 percent of the total stomach capacity, whereas the reticulorumen and omasum make up 62 and 24 percent, respectively, of the total stomach area.
Rumen papillae sites of nutrient absorption lengthen and decrease in numbers as part of rumen development. Because immature ruminants do not have a functional rumen, feeding recommendations differ for developing ruminants compared with adult ruminants. For instance, it is recommended immature ruminants are not allowed access to feeds containing non-protein nitrogen such as urea.
Developing ruminants are also more sensitive to gossypol and dietary fat levels than mature ruminants. Design nutritional programs for ruminants considering animal age. The relative sizes of various digestive system organs differ by ruminant feeding type, creating differences in feeding adaptations. Knowledge of grazing preferences and adaptations amongst ruminant livestock species helps in planning grazing systems for each individual species and also for multiple species grazed together or on the same acreage.
Concentrate selectors have a small reticulorumen in relation to body size and selectively browse trees and shrubs. Deer and giraffes are examples of concentrate selectors. Animals in this group of ruminants select plants and plant parts high in easily digestible, nutrient dense substances such as plant starch, protein, and fat. For example, deer prefer legumes over grasses.
Concentrate selectors are very limited in their ability to digest the fibers and cellulose in plant cell walls. These ruminants depend on diets of grasses and other fibrous plant material.
They prefer diets of fresh grasses over legumes but can adequately manage rapidly fermenting feedstuffs. Goats are classified as intermediate types and prefer forbs and browse such as woody, shrubby type plants.
They have a fair though limited capacity to digest cellulose in plant cell walls. On high-forage diets ruminants often ruminate or regurgitate ingested forage. As ruminants are transitioned to higher concentrate grain-based diets, they ruminate less. Once inside the reticulorumen, forage is exposed to a unique population of microbes that begin to ferment and digest the plant cell wall components and break these components down into carbohydrates and sugars.
Rumen microbes use carbohydrates along with ammonia and amino acids to grow. The microbes ferment sugars to produce VFAs acetate, propionate, butyrate , methane, hydrogen sulfide, and carbon dioxide. The VFAs are then absorbed across the rumen wall, where they go to the liver.
Once at the liver, the VFAs are converted to glucose via gluconeogenesis. Because plant cell walls are slow to digest, this acid production is very slow. Coupled with routine rumination chewing and rechewing of the cud that increases salivary flow, this makes for a rather stable pH environment around 6. When ruminants are fed high-grain or concentrate rations, the digestion process is similar to forage digestion, with a few exceptions.
Additionally, most grains have a high concentration of readily digestible carbohydrates, unlike the more structural carbohydrates found in plant cell walls. This readily digestible carbohydrate is rapidly digested, resulting in an increase in VFA production. The relative concentrations of the VFAs are also changed, with propionate being produced in the greatest quantity, followed by acetate and butyrate.
Less methane and heat are produced as well. The increase in VFA production leads to a more acidic environment pH 5. It also causes a shift in the microbial population by decreasing the forage using microbial population and potentially leading to a decrease in digestibility of forages.
Lactic acid, a strong acid, is a byproduct of starch fermentation. The acidic environment leads to tissue damage within the rumen and can lead to ulcerations of the rumen wall.
Take care to provide adequate forage and avoid situations that might lead to acidosis when feeding ruminants high-concentrate diets. Two sources of protein are available for the ruminant to use: protein from feed and microbial protein from the microbes that inhabit its rumen.
A ruminant is unique in that it has a symbiotic relationship with these microbes. Like other living creatures, these microbes have requirements for protein and energy to facilitate growth and reproduction. Each feedstuff such as cottonseed meal, soybean hulls, and annual ryegrass forage has different proportions of each protein type. Rumen microbes break down the DIP into ammonia NH3 amino acids, and peptides, which are used by the microbes along with energy from carbohydrate digestion for growth and reproduction.
Excess ammonia is absorbed via the rumen wall and converted into urea in the liver, where it returns in the blood to the saliva or is excreted by the body. Urea toxicity comes from overfeeding urea to ruminants. Ingested urea is immediately degraded to ammonia in the rumen. When more ammonia than energy is available for building protein from the nitrogen supplied by urea, the excess ammonia is absorbed through the rumen wall.
This can kill the animal. However, with sufficient energy, microbes use ammonia and amino acids to grow and reproduce. As fermentation proceeds, feedstuffs are reduced to smaller and smaller sizes and microbes constantly proliferate.
Ruminal contractions constantly flush lighter solids back into the rumen. The smaller and more dense material tends to be pushed into the reticulum and cranial sac of the rumen, from which it is ejected with microbe-laden liquid through the reticulo-omasal orifice into the omasum.
The function of the omasum is rather poorly understood. It may function to absorb residual volatile fatty acids and bicarbonate. The tendency is for fluid to pass rapidly through the omasal canal, but for particulate matter to be retained between omasal leaves. Periodic contractions of the omasum knocks flakes of material out of the leaves for passage into the abomasum.
The abomasum is a true, glandular stomach which secretes acid and otherwise functions very similarly to the stomach of a monogastric. One fascinating specialization of this organ relates to its need to process large masses of bacteria. In contrast to the stomach of non-ruminants, the abomasum secretes lysozyme , an enzyme that efficiently breaks down bacterial cell walls.
The processes described above apply to adult ruminants. For the first month or so of life, the ruminant is functionally a monogastric. The forestomachs are formed, but are not yet fully developed. If milk is introduced into such a rumen, it basically rots rather than being fermented. To avoid this problem in such young ruminants, suckling causes a reflex closure of muscular folds that form a channel from the esophageal orifice toward the omasum the esophageal groove , shunting milk away from the rumen and straight toward the stomach where it can be curdled by rennin and eventually digested enzymatically.
An orderly pattern of ruminal motility is initiated early in life and, except for temporary periods of disruption, persists for the lifetime of the animal.
These movements serve to mix the ingesta, aid in eructation of gas, and propel fluid and fermented foodstuffs into the omasum. If motility is suppressed for a significant length of time, ruminal impaction may result. A cycle of contractions occurs 1 to 3 times per minute. The highest frequency is seen during feeding, and the lowest when the animal is resting. Two types of contractions are identified:. The animation below is based on data collected by radiographing sheep Wyburn, and should impart at least some appreciation of the complexity of ruminal motility.
0コメント