Feed nutrient requirements can be classified in a short list of “major” requirements and a longer list of “minor” ones. Major nutrients include water, crude protein, energy, calcium, phosphorus, salt and fiber.
Minor, but essential, nutrients include magnesium (Mg), potassium (K), sulphur (S), iron (Fe), copper (Cu), iodine (I), cobalt (Co), manganese (Mn), selenium (Se), molybdenum (Mo), chromium (Cr), fluorine (Fl), nickel (Ni), vanadium (Vi), tin (Sn), arsenic (As), vitamins A, D and E, and essential fatty acids.
Crude protein (CP)
Protein is needed for maintenance, muscle and bone growth, and tissue repair. Elk that are rapidly growing or lactating and bulls recovering from the rut have higher protein needs. To some extent, greater protein requirements can be met by increased intake. However, the percentage of protein in diets designed for these animals is usually increased as well.
Maintenance rations should be at 10 – 12% crude protein, whereas rations for lactation or antler growth should provide 14 – 18% crude protein. Growing rations should contain 16 – 20% crude protein.
If a single diet is fed to all gender and age groups, a 16 – 17% crude protein level is optimal. Total dietary protein content must be determined to follow these general guidelines.
Like other ruminants, elk and deer can make use of non-protein nitrogen sources to satisfy part of their protein requirements. Rumen microbes transform non-protein nitrogen into microbial protein. The microbial protein in turn, as it passes out of the rumen with the digesta, becomes a protein sourced available for digestion in the lower gastro-intestinal tract.
Urea may be used to replace a portion of true protein nitrogen in an elk ration with no adverse results. In practice, total amounts of urea or ammonia (non-protein nitrogen) that could be used in a ration depends upon the roughage source.
Feeds naturally high in protein include legumes (alfalfa, clover, trefoil) and vegetable protein supplements such as roasted soybeans, soybean meal, canola meal and linseed meal. The crude protein content of a commercial feed will be displayed on the feed tag as will the proportion of non-protein nitrogen (%ECP/NPS: estimated crude protein from non-protein sources). In general, feeds containing non-protein nitrogen are less expensively priced.
Energy
Energy is derived from the digestion of several compounds, including carbohydrates and fat. Excess dietary protein can also be used as an energy source, but it is a costly practice.
Next to water, energy is the most essential nutrient, required in the largest quantity in the diet. Energy is required for all bodily functions including maintenance, growth, and activity. Lack of energy will seriously compromise health, production and reproduction.
Energy requirements of elk are commonly expressed as metabolizable energy (ME). ME quantifies the amount of energy available to the tissues after subtracting energy losses in digest and metabolic conversions. Total energy requirements are estimated by totaling the appropriate requirements for maintenance, gain, gestation, lactation or velvet production. Metabolizable energy units may expressed in kilocalories (kcal), kilojoules (kJ) (1 kcal = 4.186 kJ or mega joules (MJ). We refer to 1 MJ or ME as a “feed unit.” For example, energy requirements for a 260 kg elk female during lactation are estimated to be 80 feed units per day.
Elk will voluntarily adjust their intake to meet their energy requirements to the extent that maximal guts fill capacity permits. In a study conducted with whitetail deer fawns at Pennsylvania State University, minimal feed energy content required was 9.2 feed units; feeds of poorer quality than this should not be fed as a maintenance diet. This corresponds to an overly mature grass hay or good quality oat straw.
Energy requirements of all deer species follow a seasonal pattern. In winter, deer decrease their basal metabolic rate by 40 – 60%, thereby significantly reducing their energy requirements for maintenance. Pastured or free ranging deer increase their maintenance energy requirements by 60% in comparison to penned animals due to their increased activity.
As ruminants, elk can meet much of their energy requirements from the digestion of fibrous feeds such as hay, haulage and pasture. Smaller species, such as fallow deer, have less rumen and fiber digesting capacity than do larger deer such as red deer and elk. Fallow and whitetail deer require more concentrate (grains and supplements) and less fiber in their rations in comparison to elk and red deer.
Energy fed in excess of maintenance and production requirements will be stored as body fat. Fat deposition in deer is remarkably sensitive to photoperiod. In a Michigan study with whitetail fawns, well-fed fawns essentially stopped growing by mid-November. In contrast, fawns fed a restricted diet lost weight during the autumn. Regardless of dietary treatment, all fawns deposited fat, starting in early autumn and peaking by mid-December. However, fat reserves in the well-fed fawns were two times larger than in nutritionally deprived fawns.
Concentration of dietary energy is the strongest determinant of bodyweight gain. Cows/does must not be overfed during winter, or calving problems will increase. Rations should be designed for maintenance only. Calves should at least maintain their weight over winter.
Rations for immature elk calves can be designed to ensure winter weight gains but need to be assessed from an overall economic status. Weaned elk fed a marginal diet during their first autumn and winter will demonstrate compensatory gain on pasture the following summer. However, despite the compensatory gain on summer pasture, elk fed a marginal diet during their first winter can never catch up in body weight to elk fed a well-balanced diet throughout their growth period.
Bulls/bucks need to enter the rut in good condition since body weight losses as high as 30% are typical. Failure to build up adequate energy reserves before rutting season can compromise reproductive performance. Body weight reserves need to be built back up after the rut, after which animals can be fed a maintenance diet until antler growth begins.
Feeds relatively high in energy content include the cereal grains – corn, oats, barley and mixed grain. Corn contains the most energy of any grains. Vegetable meals such as soybean, linseed and canola meal also contain high levels of energy but are also high in protein value. Oil seeds such as soybeans and canola are high in fat and therefore high in energy content.
Elk are very susceptible to rumen acidosis caused by overfeeding of grain. Grain feeding levels need to be changed slowly to allow the rumen microbes to adapt. Similarly, changes in feedstuffs need to be introduced gradually. Elk must be closely monitored during the winter to ensure they are still consuming adequate forage to maintain rumen function.
Calcium, phosphorus and other minerals
The metabolism of calcium and phosphorus is interrelated. These two minerals are considered simultaneously when designing or evaluating a ration. Both minerals are important constituents of bone. Calcium is also essential for nerve impulse transmission, muscle contraction, secretion of some hormones and enzyme activation. Phosphorus is an essential constituent of enzymes involved in fat, carbohydrate and energy metabolism.
The actual amount of calcium and phosphorus required by elk increases greatly during growth, lactation and antler growth. A minimum of 0.7% calcium and 0.4% phosphorus is suggested for elk rations. Of equal importance is ensuring a calcium to phosphorus ratio of at least 1.5 to 1. How wide a ratio is tolerated by elk has not been researched although other ruminant species can tolerate calcium to phosphorus ratios as high as 5:1.
Calcium levels are relatively high in hay, especially legumes, but phosphorus content is quite low. Grains are the opposite, being relatively high in phosphorus and low in calcium. Rations comprised of hay/haylage and natural grains and oilseeds or meals will not provide enough minerals and vitamins. Hay analysis is required to decide which type of mineral/vitamin supplement is most suitable. Access to browse (twigs and leaves) improves natural mineral intake on pastures.
Commercially prepared mineral-vitamin supplements are extremely variable in both nutrient content and price. Follow these general guidelines.
1. Choose either a 2:1 (2 times as much calcium as phosphorus), or 1:1 (equal calcium and phosphorus) depending on forage analysis and grain feeding levels. Avoid low calcium, high phosphorus minerals as they tend to be both unpalatable and expensive.
2. Next check the levels of vitamins A, D, E, and selenium. All of these nutrients are expensive and will add to the cost. Selenium and vitamin E levels should be increased in late winter/early spring; feed vitamin levels decrease during storage and will be quite low by this time. Vitamin E and selenium are also important to prevent nutritional myopathy and to defray the stress imposed by handling. Supplemental vitamin E feeding can decrease during pasturing; fresh grass is a good source of natural vitamins.
3. Check trace element levels for copper, zinc and manganese. Elk, unlike sheep, require supplemental copper. A feed or mineral designed for sheep will not contain any added copper.
4. Check the feed tag for salt levels (if present, will be listed as sodium or Na). Some minerals include salt, others don’t. Additional salt will be necessary if no other source is provided, particularly in spring and summer. Elk will not voluntarily consume much salt in winter.
5. Lastly, decide if you need to purchase a mineral (mineral-vitamin supplement) or a premix (mineral-vitamin supplement containing higher levels of vitamins and trace minerals). If you purchase a commercial concentrate (i.e., prepared ration that already has minerals and vitamins added), a mineral will be sufficient. If, however, you are supplementing with straight grains, a premix is preferable.