RED DEER – When estimating animal feed digestibility and quality, the newest approach measures total digestible nutrients and energy in a sample.
The estimates have gone beyond measuring protein or the relative feed value, which is an estimate of how much dry matter the animal might consume, said an Agriculture Canada ruminant nutritionist.
“A lot of people equate quality with protein,” said Karen Beauchemin, at a feed and forage conference here Dec. 3.
“And often, high protein feeds are also high in energy so sometimes protein goes hand in hand with energy,” she said.
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It is important to get a laboratory analysis to appraise the chemical content and nutrient quality of feed. The analysis measures moisture, dry matter, nutrients, protein, fibre and energy content, all necessary for good livestock nutrition.
At one time, diet formulations were based on crude protein content, but it is also important to know how much is actually available to the animals. Protein is a major component and comes in two forms – bypass and rumen protein.
Bypass protein is not degraded in the stomach but gets digested in the small intestine and becomes a good source of amino acid.
The larger fraction of the protein is digested in the rumen by the microbes. It becomes a source of nitrogen for the microbes. They grow in the presence of this energy and are digested in the lower gut as protein.
Most forages and grains don’t deliver enough protein, so animals, especially dairy cows, young growing animals and those providing milk to calves, need supplements.
“They can’t eat enough to satisfy their energy requirements,” she said.
Peas are 20 percent protein and 52 percent starch. They are good for dairy cows but the protein is extremely degradable so there is a limit to how much should be fed to a dairy cow. No more than two to three kilograms of peas per day are recommended.
Canola or soybean meal, corn gluten, blood meal, urea, as well as meat and bone meal are high in bypass protein. However, meat and bone meal is banned for ruminant use so other products must be found.
Many Alberta animals receive their energy from barley. The energy released depends on whether it was processed properly.
Too much or too little processing causes problems. Overprocessed barley is digested too quickly and can lead to metabolic problems causing animals to go off their feed. Underprocessing does not provide full energy value because too many whole kernels are passed in the manure.
Minerals should make up about 10 percent of the feed and levels should be measured in case of deficiencies like copper or selenium. These may be added through supplements.
Animals also need energy, some of which comes through fat.
Canola seed is high in fat but most meals have had most of the oil removed for human consumption.
More dairy producers are looking at feeding whole or rolled sunflowers. They are high in crude protein at 19.2 percent, with 44 percent fat. The fat is linoleic acid, a valuable human food component because it fights cancer.
“Feeding sunflower seeds is a very good way of incorporating fat into a diet. It is easier than adding tallow to a diet,” Beauchemin said.
Flax seed is 25 percent crude protein and 32 percent fat. The fat is linolenic acid, which improves animal fertility. All good diets contain fibre.
Forages with long particle lengths of no more than five centimetres stimulate chewing and the production of saliva and hence, buffer the rumen against excess acid. A good dairy cow produces 200 litres of saliva per day.
Grains are rapidly digested and create a lot of stomach acid, so fibre from hay, straw or silage is critical.
Feedlot animals receive higher levels of grain so they must eat forages to keep metabolic diseases at bay. Conditions like acidosis can be curbed with adequate fibre.
“This will be a real issue in the future as we move away from subtherapeutic levels of antibiotics in beef cattle production,” Beauchemin said.
Producers may still provide ionophores or rumensin but animals will require more forage rather than medications for rumen health.
It is important to know what kind of fibre is present. When a feed analysis is done, a measure of neutral detergent fibre and acid detergent fibre are provided. Acid detergent fibre is found in cellulose, which is easy to digest. However lignin, a less digestible fibre, may bind to it.
As protein content decreases, acid detergent fibre increases.
When looking at cereal based silage, fibre shortens as plants mature and more kernels are available. Kernels contain more starch.
Beauchemin suggested cutting crops for silage about a week after heading to maintain quality and provide adequate fibre and energy.
