While too much fibre in forages can limit feed intake in feedlot cattle, too little in the diet can destabilize the rumen and lead to digestive upsets.
This happens when rations include a high level of grain, typical of finishing rations. Overprocessing the grain, whether it be with a hammer mill, roller mill or steam-flaking (tempering with steam before rolling), to obtain a more consistent appearance can amplify the problems by increasing the rate of digestion, while doing little to increase the utilization rate.
All types of grains play the same role by providing energy in the diet. We process grain to crack the kernel so rumen microbes have easy access to the starch to achieve a good level of digestibility, explains Murray Feist, provincial ruminant specialist with the Saskatchewan Ministry of Agriculture.
Processing can increase utilization of cereal grains by as much as 25 per cent, with the exception of oats, which have a different structure with more fibre content than barley, corn, wheat and triticale. Processing oats may only increase utilization by five per cent for calves and 10 per cent for cows because of the fibre content of oat hulls.
There s no question of the need to process barley and corn grain in feedlot diets, says Dr. Greg Penner, assistant professor of ruminant nutrition at the University of Saskatchewan. About 30 per cent of the dry matter in unprocessed barley can end up in the feces and the cost of processing is currently lower than the cost of the lost barley. However, research shows there is no benefit to processing barley beyond cracking the kernel. The same recommendation is commonly applied to wheat and triticale grain.
Overall, unprocessed corn is better utilized than unprocessed barley, though we do see differences in steamfl aked or high-moisture corn as it is more available in the rumen than whole corn or dry-rolled (crack) corn.
Forages are really an inconvenience from the feedlot perspective because they are bulky to handle, expensive on a cost-per-energy basis, and decrease feed conversion, Penner explains. But when we look at the essential role forage plays in maintaining healthy rumen function, not including forages in finishing rations comes down to an animal health and welfare issue.
Feist says the fibre in forage stimulates cud chewing and with it the production of saliva that buffers the acid in the rumen. Feeding grain alone destabilizes the rumen because it increases the production of fermentation acids and lowers the pH level in the rumen, gradually leading to an increase in lactic acid. In turn, this upsets the balance of rumen bugs as those that like an acidic environment survive and the others are wiped out. Excess acid can also have a burning effect on the inside of the rumen wall. This can lead to ulcers on the rumen wall raising the potential for certain types of bacteria to enter the blood and cause liver abscesses or lameness.
There is definitely a dose and time relationship, Feist adds. An abrupt, excessive dose of carbohydrates in a short period of time can be dangerous, causing acute acidosis and death. In chronic cases, you may notice watery diarrhea, bloating, variable feed intake and signs of toxic shock, such as stiffness and depression. Cattle can tolerate being more acidic when carbohydrate levels are increased gradually over longer time periods.
Managing forage to optimize value
Cereal silage is the most common forage fed by feedlots in Western Canada. Given its importance in the diet, and the cost, its quality should be as high as possible.
Total dry-matter yield is important, but harvesting for maximum digestible energy will optimize its feed value. The best energy and protein levels for cattle feed (for swath grazing, greenfeed and silage) is captured in barley cut at the soft-dough stage and oats at the late-milk stage, which is also the window to minimize fibre content.
The ensiling process relies on anaerobic fermentation caused by lactic acid bacteria quickly dropping the pH level of the silage, thus preserving its quality similar to the pickling process, says Penner.
Adding a commercial silage inoculant, most commonly natural lactic acid bacteria, at the harvester has been shown to help to improve the consistency of fermentation throughout the silage mound and reduce dry-matter losses. To a lesser degree, it may improve animal performance by improving feed efficiency, dry-matter intake and gain.
An inoculant can be most beneficial when forage conditions are less than ideal, however, its effectiveness will depend upon many other factors that affect silage quality at harvest, in storage and when it is fed.
The ideal moisture content for ensiling is 60 to 65 per cent. Too wet and nutrients can leach out and concentrate at the base of the pile. Too dry and there is a risk of mould and heating, which destroys feed value.
Chop length is important when it comes to packing the silage. The ideal is three-quarters of an inch, though that depends on the type of forage.
Proper packing with a tractor to push the air out of the mound as the forage is delivered is critical. The idea is to form a dense mound that resists oxygen penetration during fermentation and feed out. The recommendation is to pack for one to three minutes per ton of fresh forage layered six to 12 inches thick.
There is no longer any question that a good, tight covering protects the mound from air, water and wind to expedite anaerobic fermentation and goes a long way to preventing spoilage in stored silage. A plastic sheet or a tarp held down with about 20 tires per 100 square feet of surface is adequate.
Research shows dry-matter losses can be as high as 70 per cent in the top three feet of a mound. Fifteen to 25 per cent of the silage can be in the top three feet, depending on the shape of the mound. Spoiled silage at the top of the pile will be black with a slimy texture and a foul odour and has a high pH and fibre content. Spoilage at the bottom of the pile is usually yellow to orange in colour with a strong acidic odour and low pH.
Last, but of equal importance, is proper face management at feed-out, says Penner. Calculate how much silage will be fed each day to estimate the depth you have to go into the face at each feeding. The goal is to maintain a nice flat face in removing silage from the top to the bottom to minimize the area exposed to the air each day. Tunnelling into a pit not only allows oxygen to penetrate into the mound, but can present very dangerous working conditions should the overhanging material collapse.
Contact Greg Penner at 306-966- 4219, or Murray Feist at 1-866-457- 2377.