In particular, the nutritive value of oats is largely determined by the percentage of hulls in the grain, which varies from 20 to 30% of the kernel weight (up to 45%) and depends on genotype and environment (Cuddeford, 1995). Oats are much richer in gross energy than other cereals (for example 19.5 MJ/kg vs. 18.7 MJ/kg DM for maize), due to their relatively high oil content (3.5-7.5% DM). Oats contain more protein than maize (8-15% DM), but less than wheat and barley. Oats have a good amino acid profile that compares favourably with those of other cereal grains. Notably, the lysine content of the protein is much higher (4.3% of the protein vs. 2.9% for wheat), and sulphur-containing amino acids, threonine and tryptophan are also well represented. Oats contain much less starch (about 40% DM) than maize, wheat and barley.
Naked and dehulled oats have a starch content close to that of barley (about 60% DM) and a protein content similar to that of wheat (more than 12% DM). There are also high-oil naked oats, with an oil content 5-6 times greater than wheat (MacLeod et al., 2008). The oil is mostly found in the endosperm and contains a large amount of unsaturated fatty acids (Assefa, 2006; Peterson, 1992 cited by Rines et al., 2006). The major fatty acids are linoleic (18:2), oleic (18:1) and palmitic (16:0), which together account for over 90% of the total fatty acids (Welch, 1995).
Unlike other major cereals, oats have a very high fibre content due to the presence of hulls. The ADF content of oats is about 16% DM vs. 3-4% for maize and wheat and 6% for barley. The lignin content, while still low (less than 2.5% DM), is twice that of wheat and barley. The presence of hulls and their high fibre content make oats inferior to other cereal grains for high producing livestock, both due to their bulk and to the lower digestibility and energy density. Oats remain a valuable feed, for example for young ruminants, poultry, sows and horses. In some cases, processing can help to improve their feeding value (Boyles et al., 2006). Naked oats as well as hull-less genotypes developed in the last decades of the 20th century contain considerably less fibre (ADF less than 6% DM) and have a better nutritive value (Assefa, 2006; Boyles et al., 2006).
Large high starch-containing meals are a significant risk factor for gastric ulcers in horses. Oats are rich in pentosans (including ß-glucans), which are polymers of pentose sugars that increase diet viscosity. They can cause digestive problems in monogastric species.
Oats are often processed to improve their feed value:
- Cold treatments (dehulling, grinding, rolling and cracking). Dehulling oats produces groats. Crimping oats (a light crushing process that breaks the oat hulls) is particularly popular in horse feeding.
- Hot-dry treatments (extruding, micronising, roasting and popping).
- Hydro-thermal treatments (steam-rolling, steam-flaking, pressure cooking and exploding).
- Chemical treatments (sodium hydroxide, formaldehyde) (Chakraverty et al., 2003; Cuddeford, 1995).
Oats are a choice feed ingredient for horses and are often the standard by which other grains are evaluated (Cunha, 1991). Oats are fed in mixtures with other grains and by-products, or they can be fed as the sole grain, sometimes with roughage such as alfalfa hay or chaff to maintain a horse at pasture during winter, or when fed out in controlled amounts during drought conditions. Oats have a soft kernel that make them easier for horses to chew than other cereals (Kohnke et al., 1999). For that reason, they are palatable to horses and ponies, who prefer them to other grains in preference testing (Houpt, 1983; Hawkes et al., 1985). When oats are the only grain in the diet, as is the case in traditional feeding systems, they are safer than other cereals as their low density and high fibre content make them more difficult to overfeed, and the grain size is more appropriate for chewing. A greater quantity of oats than of the other grains must be consumed to cause founder or other digestive problems. This property also makes them easier to use for novice horse feeders (Frape, 2004).
However, the higher fibre content of oats makes them less digestible than barley and maize, with a lower digestible energy value. This low energy density increases the bulk that has to be fed to high-performance horses and small-frame horses. Horses with a poor appetite when worked hard may not be able to meet their energy requirements. Oats are also more expensive per unit of energy (Kohnke et al., 1999). Naked oats have a higher nutritional value, but it is preferable to restrict them at 10-20% of the cereal mix (Frape, 2004). In some countries, it has been traditionally recommended to store new oats for 2 or 3 months before feeding to prevent digestive troubles, though there is a lack of supporting evidence (Cuddeford, 1995).
Whole oats contain the lowest amount of starch but the highest proportion of starch digested in the small intestine, ranging from 61-83%, followed by sorghum, maize and barley. For that reason, processing oats by crimping, rolling or grinding does not significantly improve the digestibility of oat starch in the small intestine (Kohnke et al., 1999). Some authors consider that processing is useless and uneconomic when the teeth are in good condition and the animal is more than one year-old (Frape, 2004). It was shown that cutting and sieving oats did not affect nutrient digestibility (Lopez et al., 1988). However, rolling or crimping were shown to improve DM digestibility by about 5% (Cuddeford, 1995). Thermal processes such as steam-flaking, micronising or extrusion have been reported to increase nutrient digestibility by 2-5% (Lewis, 1982 cited by Frape, 2004; Householder et al., 1976 cited by Cunha, 1991). When compared to crimping, micronising improved protein digestibility by 2-3% (Klendshoj et al., 1979) and increases in precaecal starch digestion by 14% have been measured (Householder et al., 1977 cited by Cunha, 1991).
Typical analysis (dry matter):
⦿ Protein 11%
⦿ Oil 5%
⦿ Starch 41%
⦿ Sugar 2%
⦿ Calcium 1 g/kg
⦿ Phosphorus 4 g/kg
⦿ Iron 110 mg/kg
⦿ Total Energy 19.5 MJ/kg
➡️ High energy
➡️ Quality protein
➡️ Low iron
➡️ Prone to mycotoxin contamination
➡️ Gastric ulceration risk
➡️ High starch