Rice bran is a misnomer, or rather a confusing term because it can encompass a range of rice by-products at variable concentrations. But rice bran it is, and this name has prevailed in literature and commerce. It is a very atypical ingredient: it has excellent nutritive value, but it is undervalued by most nutritionists; it is widely available, but hardly traded in the commodities market. Understanding how rice bran is produced and its problems will help nutritionists seek out this eccentric ingredient and use it in pig and poultry diets with confidence.
The rice milling process
It all starts with rice grain as it arrives from the field. The rice we grow and the rice we humans eat do not look the same. Field rice comes with a tightly attached outer husk or hull, very much like barley and oats. Removing the hulls is the first step in the rice milling industry. Unlike other similar cereals, rice has hulls extremely rich in silica (silicon dioxide), better known as quartz or sand. As such, rice hulls are immensely abrasive not only on the feed mill machinery, but also inside the animal.
Consumption of rice hulls at sufficient quantities can cause diarrhea (best case scenario) and internal bleeding (worst case scenario). Obviously, the damage increases with ingested volume. As such, it strongly prohibits using rice hulls in diets for pigs and poultry — even at the slightest concentration. Most rice mills use rice hulls as a source of energy as they burn it to produce heat or electricity, or both. Lamentably, some mills incorporate some part of their rice hull production into rice bran, and this is the first reason why some such products fail. To this end, it is recommended to test incoming rice bran for silica according to volume and frequency of loads.
Field rice comes with a tightly attached hull that is rich in silica. | Indiatraveler, Dreamstime.com
When the hulls are removed, we are left with a brownish grain — also known as brown rice. This looks very much like wheat, and like wheat, it is very hard to boil and chew. Thus, the outer brown layer, which is rich in fiber (the hard to chew part), is removed. This is the actual “bran,” again equivalent to wheat bran, even in the profile of the fiber: it is rich in pentosans, especially arabinoxylans. Because of this, it should be equally beneficial to use a wheat-specific enzyme when high levels of rice bran are used. Most likely, this is going to benefit more poultry than pigs, but all these assumptions require documentation.
Removing the outer hull leaves a brownish grain. | Airborne77, Dreamstime.com
Further down the rice milling process, the embryo is removed. Rice grain is a seed, after all, and contains an embryo that will give a new plant — the rest are its first food. This embryo is rich in protein and oil. Removing them leaves the rice we consume, which is practically a starch-rich staple. In some instances, especially in Asia, rice oil is extracted, but in most cases, the embryos are blended with bran. This is a desirable process, but it can also be the root of many troubles. Along with the oil, there are a good amount of enzymes that oxidize it (used by the new seedling to obtain its first energy “drink” before starch is mobilized from afar). These lipoxidases start acting as soon as they are exposed to the air, and this happens when the embryos are torn apart during the milling process. Thus, rice bran contains high levels of oil, which gives it high nutritive value for animal feeding, but this oil might be highly oxidized, which causes feed refusal by animals — especially young ones. To prevent this, an antioxidant should be added at the rice mill, but this is seldom done, perhaps due to cost or lack of mixing abilities. If unprotected, full-fat rice bran (as it is often called) will oxidize rapidly unless it is consumed within days from its production.
The final product
To arrive at the highly glossy rice we buy at the supermarkets, rice mills must polish the final product. This is achieved by friction using calcium carbonate. This is why when we rinse rice before cooking it the water is cloudy. The amount of calcium carbonate used is minimal, but it should be taken into account as this mineral is used in many nutrition products, such as soybean meal to increase flowability, and vitamin, mineral, medicinal premixes as a carrier and diluent. Thus, calcium laboratory analysis is required to ensure the correct calcium level is entered in the feed formulation matrix. Rice polishing leaves behind a dust of calcium carbonate and starch, which are again added into wheat bran, without diminishing its quality — but they do come at a very distinctly finer particle size so separation could be an issue if embryo-derived oil is not in the mix to keep everything “in suspension.”
White rice is a polished grain that is mostly starch. | Andrey Ospishchev, Dreamstime.com
The final thing we must be aware of rice bran is that it is a cereal rich in phytate. In other words, it contains negligible amounts of digestible (pigs) or available (poultry) phosphorus. Only 12 percent of total phosphorus is of any use to these animals — the rest is excreted in the manure. Adding the enzyme phytase will most likely benefit any diet containing rice bran, but perhaps an extra dose might be warranted — again a very nice theory that requires input from those most interested in this business: the phytase suppliers. As it stands, rice bran-based diets require increased supplementation with phosphates (mono- or di-calcium phosphates), which should not be a problem for most mills, unless a concentrate of micro-ingredients already containing phosphate is used. In this case, the mill will need to provide for an additional/occasional ingredient: a phosphate to be used in diets rich in rice bran.
In conclusion, rice bran is a valuable ingredient as it contains about 14 percent crude protein, 7 to 10 percent crude fiber and up to 17 percent oil. This gives it a net energy concentration of 10 MJ/kg for pigs, and a metabolizable energy of 11.5 Mj/kg for poultry. Absence of any hulls and stabilization of the oil will ensure a high-quality product that can be used at levels restricted only by its fiber concentration in all diets for pigs and poultry.