By David Haugh, Wellsford Vet Clinic
Cellulose in plant fibre is the hard-to-digest carbohydrate that animals like us cannot use at all. But ruminants such as cattle, sheep, goats and deer are designed to have a way around that. Their digestive system effectively grinds away at cellulose. That’s great when you have lots of grass and hay to eat, but the downer is that the same digestive system can spiral out of control to self-destruction if too much easily digested carbohydrate is eaten.
Things like bread, grains, molasses, stock “nuts”, apples, kiwifruit, potatoes, kumara, turnip or swede bulbs, finely chopped maize silage and even whey can potentially lead to an intake of too much sugar and starch. Ruminants’ digestive tracts can gradually adapt to higher sugar/starch intake levels so an intake that is toxic initially can be safe at another stage. Also, they cope better if they already have a high fibre diet. How much is safe to feed is the $60 million question.
Here are some ballpark figures for feeding grain … 50g/adult sheep/day to start with increasing to 300g/adult sheep/day over a 3 or 4 week period. Adult cattle can start safely on 1kg/day. Make sure no individual is “pigging out” and eating more than their share.
Ruminants’ digestive tracts are very different from ours. Before food reaches their fourth stomach (the equivalent of ours) it goes into the reticulorumen, or the “paunch”. This is effectively a huge vat of food, water, friendly bacteria and protozoa, and a few potentially not so friendly bacteria. The bacteria and protazoa are the ones that slowly digest the cellulose. They produce volatile fatty acids which the host animal will absorb into the bloodstream and use as an energy source. Like all acids, the volatile fatty acids lower pH and a happily functioning reticulorumen will be slighty acidic. Because the animal can absorb the acids away as quickly as they are made and because there are some antacids in saliva, which the animals produce when eating fibrous food, everything stays in equilibrium.
However, if you add too much sugar or starch, the production of fatty acids will outstrip the animal’s ability to remove them from the reticulorumen. Over the next few hours, the pH starts falling. Many of the “friendly” bugs die and “bad” ones now thrive and produce lots of lactic acid. The pH falls even further and water is drawn into the reticulorumen from the blood. It sounds sloshy if you push on it (left side of abdomen) and there is pain and dehydration. Irritability progresses to dullness. Most animals that go down and won’t stand are going to die without major veterinary intervention. Less severe cases may lead to laminitis (“founder”) or bacteria crossing from the reticulorumen into the blood stream damaging a number of organs. Treatment of less severe cases is based on removing the offending food, offering hay, withdrawing water for 12-18 hours and giving antibiotics, painkillers and antacids.