Je, ni vyema kua mnyama-mcheuzi?

There is no animal that can digest and get nutrients from plants by themselves because most of the nutrients are tied up as cellulose. Cellulose is a complex and fibrous carbohydrate found in the cell walls of plants. All animals that eat plants have bacteria somewhere in the system that help them to break down the plant material so that they can absorb it. This process is similar to fermentation and it can either happen before the main stomach where acids help in digestion, or after the stomach. We call these two options either foregut fermentation or hind-gut fermentation depending on where it happens.

Most of us are familiar with the ruminants. All the antelopes, goats, sheep, and giraffe are ruminants. Our common hind-gut fermenters are the zebras, rhinos, elephants and hyraxes. 

Ruminants have a special digestive system that involves four stomach chambers that help them digest cellulose. In ruminants it occurs in the first chambers of the ruminant system. When a ruminant eats, it first basically just swallows the food and it goes into the rumen, the first chamber. Once this is full, the animal settles down to chew the cud. The coarse plant matter is regurgitated and re-chewed and mixed with saliva that keeps it at the right pH for the bacteria. In the case of buffalo, this means producing up to 100lts of saliva per day. Meanwhile, the rumen contents are being stirred, the finest chewed food sinks to the bottom where it passes through the reticulum into the omasum where it is filtered again before being pumped into the real stomach called the abomasum. This is why the particles in ruminant dung are so fine.

Bacteria reproduce very quickly and in large quantities because they do not live very long. The bacteria that are constantly reproducing also provide an excellent source of protein when they die, this is important because animals need protein in order to survive.

Hind-gut fermenters are generally not as efficient as foregut fermenters in getting nutrition from plants. In non-ruminants the fermentation happens in a part called the ceacum. Some hindgut fermenters like hares eat their feces again so that it goes through their system twice. This is called coprophagy.  In zebra and elephant, before a baby can start to eat and digest plants, it usually eats some of its mother’s dung, so that it gets the right bacteria in the stomach.

Is one system better than another? As always, the answer isn’t a straight yes or no. Most of the time, ruminants are able extract more nutrition out of their food than the hind-gut fermenters, but as the quality of the food they eat decreases it gets to a point where as efficient as they are, the food just doesn’t have enough nutrients for them. Because of having to wait for the whole rumination process to happen before they can eat more, they start to suffer. Meanwhile, the hind-gut fermenters like zebras don’t have to stop to chew the cud and for the rumen to empty so they can just increase how much they eat. This is why you will often see big herds of zebra hanging around when the wildebeest have already moved in search of greener grass.

The other advantage of rumination is that ruminants can quickly fill their rumen and then continue the digestion process while they are alert to predators.

Swahili version

Hakuna mnyama mwenye uwezo wa kumeng’enya na kupata virutubisho kutoka kwa mimea peke yao kwa sababu asilimia kubwa ya virutubisho vipo kwenye ‘cellulose’. ‘Cellulose’- nyusi-nyusi kwenye mimea – ni wanga tele inachopatikana kwenye kuta za chembe ya mimea. Lazima wanyama wote wanaokula mimea wawe na bakteria kwenye mfumo wa utumbo kuwasaidia kumeng’enya ‘cellulose’ ili waweze kuvifyonza virutubisho. Mfumo huu unafanana na uchachukaji na unaweza kutokea kabla ya tumbo yenye asidi (tindi kali) ya kumeng’enya, au baada ya tumbo ya asidi. Tunaiita mifumo hiyo miwili uchachukaji wa mbele (‘foregut fermentation’) au uchachukaji wa nyuma (‘hindgut fermentation) kutegemeana na sehemu uchachukaji hutokea.

Wengi wetu tunawafahamu wanyama-wacheuzi (‘ruminants’). Paa wote, mbuzi, kondoo, ng’ombe, na twiga ni wanyama-wacheuzi. Wachachuaji wa nyuma wa kawaida ni punda milia, kifaru, tembo, na pimbi. 

Wanyama-wacheuzi wana mfumo wa utumbo inayohusisha sehemu nne za kumeng’enya ‘cellulose’. Kwa wacheuzi hawa, uchachuaji unatokea kwenye tumbo sehemu ya kwanza. Mcheuzi akila, hua anameza chakula bila kuyatafuna na inaingia kwenye sehemu ya kwanza kinachoitwa ‘rumen’. ‘Rumen’ ikijaa, mnyama anatulia kucheuwa na kurudia kukitafuna haswa nyenzo mgumu. Anavyoendelea kucheuwa mate yake huchanganyika kwenye chakula na kuhakikisha kiwango cha pH kinabaki kwa kiwango nyeti kwa ajili ya bakteria kuishi. Kwa mfano wa nyati, inamsababisha atoe karibia lita mia za mate kwa siku. Wakati anaendela kucheuwa, chakula kwenye ‘rumen’ inakorogwa, na vipande vidogo vinashuka hadi chini vinapopita kwenye sehemu ya pili kama chujio inayoitwa ‘reticulum’ hadi kwenye sehemu ya tatu inayoitwa ‘omasum’ endapo inaingia kwenye tumbo ya asidi inachoitwa abomasum. Hii ndiyo maana kinyesi cha wacheuzi kinakuwa kimesagika sana.

Bakteria (vijimea vidogo sana) inazalishana haraka sana na kwa kiasi kikubwa kwa sababu haiishi muda mrefu. Bakteria inazalishwa kila wakati na ikifa ni chanzo cha ‘protini’ , pia ni muhimu kwa wacheuzi kwa sababu wanyama wanahitaji ‘protini’ kuishi.

Wachachuaji wa nyuma huwa sio wameng’enyaji fanisi kama wachachuaji wa mbele kwa kutoa virutubisho kwenye mimea. Kwenye wala-mimea wasio wanyama-wacheuaji, uchachuaji wa chakula inatokea kwenye sehemu ya utumbo inachoitwa ‘cecum’. Kuna wacheuaji wengine kama sungura wanaorudia kula kinyesi chao ili chakula kipite kwenye mfumo wa utumbo mara ya pili. Tendo hii inaitwa ‘coprophagy’. Kwenye wanyama kama pundamilia na tembo, kabla mtoto kuweza kuanza kula mimea inabidi ale kinyesi cha mama yake ili apate bakteria tumboni ya kumsaidia kumeng’enya chakula.

Je, kuna mfumo unaofaa zaidi? Kama kawaida, jibu siyo ndiyo wala hapana. Kawaida wanyama-wacheuaji wanaweza kupata virutubisho ziaid kwenye chakula chao kuliko wachachuaji wa nyuma, lakini kipindi chakula chao kikipungua inafika wakati ufanisi wao hautoshi kupata virutubisho ya kutosha kutoka kwenye chakula chao kikavu. Wanaanza kuteseka kwa sababu ya mfumo wakuhitaji kusubiri chakula kuyeyushwa kabla ya kuweza kula zaidi. Wakati huo huo, wachachuaji wa nyuma kama pundamilia hawahitaji kusubiri kucheua mlo wao, na wanaweza kuongeza kiasi cha mlo. Hii ndiyo maana mara nyingi utakuta punda wanabaki sehemu wakati nyumbu wameshaondoka wakitafuta majani mapya.

Faida nyingine ya ucheuaji ni kwamba wanyama-wacheuaji wanaweza kujaza ‘rumen’ haraka halafu kuendelea kumeng’enya chakula chao wakati wanakua makini kutafuta adui.

Main source:

From The Biology of African Savannas, by Brian Shorrocks.