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Oat hulls and oat mill feed

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Description
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Common names 
  • Oat hulls, oat husks [English]; balle d'avoine, coques d'avoine [French]; cascarilla de avena [Spanish]
  • Oat by-products, oat mill feed [English]; rémoulages d'avoine [French]; harinillas de avena [Spanish]
  • Oat bran [English]; son d'avoine [French]; salvado de avena [Spanish]
Related feed(s) 
Description 

Oats (Avena sativa L.) are a major cereal worldwide and the 6th cereal grain after maize, rice, wheat, barley and sorghum (FAO, 2011). The main use of oat grain is as animal feed, alone or in mixtures. Oats are not suitable for breadmaking but are consumed in breakfast cereals and as porridge, hard, or added to other dishes as a thickening agent. The preparation of oats for human consumption is more laborious than for wheat because oats must be milled to remove the glumes before any further processing can be carried out (Suttie et al., 2004). Oat milling yields several by-products:

  • Oat screenings result from the cleaning of raw oats before processing.
  • Oat hulls (lemma) are obtained by the mechanical separation (rotating drum) of the hulls from the kernels prior to milling. Oats may be steamed or roasted before that step to facilitate separation. The hulls are removed by air aspiration and the groats, which are the edible huskless grains, are ready for further processing (Bühler Group, 2007; Suttie et al., 2004). Oat hulls include small fragments of endosperm and represent up to 25% of the weight of the grain (Thompson et al., 2000).
  • Oat mill feed, also called oat dust, is obtained after the transformation of groats into oatmeal. Groats are kiln-dried, sized and cut, producing fines that are mixed with the screenings and the hulls obtained previously. The final ground product, called oat mill feed, is usually intended for animal feeding (Bühler Group, 2007).
  • Oat bran is a by-product of oat flour production. It is used as a health food for human consumption due to its hypoglycemic and hypocholesterolemic effects and high content of B vitamins (Sadiq Butt et al., 2008; Webster, 1986).

It is important to note that oat hulls and oat bran are completely different products: oat hulls are a high fibre, low protein and low energy feed while oat bran is a low fibre, high protein and high energy food ingredient. However, the name oat bran is sometimes used as a generic term for more or less fibrous oat by-products, which may be a source of confusion.

Oat hulls, oat mill feed and other oat by-products do not have universally accepted definitions and clear boundaries. Some national official regulations contain mandatory requirements on their composition, but ingredients sold under those names often encompass a wide range of by-products ranging from pure hulls to mixtures of hulls, screenings, and residual endosperm particles.

Due to their high fibre content, oat hulls and oat mill feed are mostly valuable for ruminant and rabbit feeding. They can be used in concentrate pellets (Winfield et al., 2007). Oat hulls can replace sawdust as an alternative bedding material for dairy cattle (Shane et al., 2010). Oat hulls are also a potential raw material for bioethanol production (Perruzza, 2010). Oat hulls mixed with excreta can be used to produce biogas and their methane yield is comparable to that obtained with straw (Kusch et al., 2011).

Distribution 

Oat processing by-products are traded feed commodities.

Processes 

Oat hulls are a highly fibrous material and like other roughages their nutritive value can be enhanced by various chemical (alkali) and enzymatic treatments (see Ruminants below).

Nutritional aspects
Nutritional attributes 

Oat hulls and oat mill feed

Oat hulls are a high fibre feed that contains about 75% NDF, 26% ADF, 30% crude fibre and 7% lignin. Its protein content is low (6%) and its protein is not a particularly valuable source of amino acids. It is considered as a source of insoluble fibre for ruminants and rabbits and is often compared to a low quality roughage in terms of nutritive value (Fraser et al., 2004). However, there is a continuum of composition between oat hulls and the other by-products of oat millings: oat hulls may actually contain important amounts of starchy endosperm and oat mill feed may contain large amounts of hulls. Oat mill feed is typically a little richer in protein (8%), richer in starch (25%) and poorer in fibre (22%) but its composition is extremely variable.

Oat bran

Oat bran has a higher nutritive value than other oat by-products due to its much higher protein content (15-20%) and much lower fibre content (ADF less than 5%). An important part of oat bran fibre consists of beta-glucans, which are non-starch polysaccharides (Sadiq Butt et al., 2008). Oat bran is a food rather than a feed ingredient, but it features in several animal nutrition studies due to its content in soluble dietary fibre.

Potential constraints 

Trichothecenes T2 and HT2

Both T2 and HT2 toxins can be present in oats and oat by-products. These toxins, produced by Fusarium fungi, cause a wide range of symptoms including weight loss, feed refusal, dermatitis, vomiting (cats, dogs, pigs and ducklings), diarrhoea, haemorrhages and epithelium necrosis in various organs (stomach and intestine, bone marrow, spleen, testis and ovary) (European Commission, 2001). Between 2005 and 2009, a survey of European oat mills found that while the processing of oats to oat flakes and oat meal reduced the levels of T2 and HT2 trichotecenes toxins by more than 80%, toxin levels in oat by-products increased by 3-4 times and ranged from 282 to 564 µg/kg. Because these relatively high levels could potentially cause chronic or acute toxicity (at 0.06 mg/kg BW) in small animals, their use as feed ingredients merits further investigation (Pettersson et al., 2011; European Commission, 2001).

Ruminants 

Nutritive value

Because of their high level of lignified cell-walls and low protein, oat by-products that contain hulls have a low nutritive value and are typically used in ruminant diets to replace forages. Many studies have compared the nutritive value of oat hulls with that of other sources of fibre.

Dairy cows

When included as a concentrate at 50% in dairy cows diets (forage:concentrate 1:1), oat hulls resulted in lower digestibility, milk yield and energy retention than other ingredients (soybean hulls, apple pulp, Jerusalem artichoke tubers, molasses and wheat). They did not provide enough fermentable energy for microbial synthesis and their use resulted in a higher urine-N:ingested-N ratio (Hindrichsen et al., 2006) and lower methane production (Hindrichsen et al., 2004).

Sheep

In sacco DM degradability of oat hulls (particle turnover of 0.06 h-1) is about 40%, lower than that of soybean hulls (50%) and much higher than that of sunflower hulls (22%) (Pereira et al., 1999). Oat hulls showed a lower rate and a smaller 36h-extent of in sacco DM disappearance (0.8 h-1 and 66% respectively) than maize fibre or soybean hulls (about 7%/h and 90%). In vivo digestibility of OM, NDF and ADF in diets containing 80% seed hulls or maize fibre were lower for oat hulls and cottonseed hulls (less than 50%) than for maize fibre and soybean hulls (more than 75%) (Hsu et al., 1987).

In vitro

The nutritive value of oat hulls estimated by in vitro measurements was found to be lower than that of maize fibre and soybean hulls, but slightly higher than that of cottonseed hulls. In vitro DM disappearance of oat hulls was much lower than the values obtained for maize fibre and coarse maize fibre (32%, 86% and 82% respectively) (Garleb et al., 1988).

Processing

Chemical and enzymatic treatments can improve the values of oat hulls. In growing steers, ammonia treatment (3% DM basis) increased the in situ potential degradability and degradation rate of NDF and ADF fractions, in vivo NDF digestibility as well as voluntary intake (Thompson et al., 2002). Alkali treatment increased in vitro and in sacco DM disappearance (Garleb et al., 1988; Pauly et al., 1992). In dairy cows, alkaline hydrogen peroxide treatment increased the in vivo OM and cell wall digestibility in diets containing from 20 to 60% treated oat hulls (Cameron et al., 1991b; Titgemeyer et al., 1991). This treatment increased digestible DM and fibre intake, and maintained growth in heifers (Cameron et al., 1991b) and milk production in dairy cows (Cameron et al., 1991a). Enzymatic treatments can enhance the in vitro (rumen fluid) DM degradation compared to wheat straw and alfalfa hay (Yu et al., 2005).

Other feed uses

Oat hulls have been proposed as a structure-enhancing ingredient for the storage of root peelings (beets, carrots, potatoes) when mixed with urea and molasses. Such feeds could be used as a supplement for dairy cows and as a sole feed for fattening bulls (Dornow et al., 1991).

Pigs 

Oat hulls

Growing pigs

Oat hulls are rich in insoluble dietary fibre and have been tested in small amounts in pig diets for the preservation of health. In weanling pigs, oat hulls included at 2% dietary level decreased the incidence of post-weaning diarrhoea caused by an imbalance of carbohydrate and protein entering the hindgut (Kim et al., 2008). This protective effect could be due to changes in the intestinal microflora/fauna (Kim et al., 2005). A similar positive effect on the reduction of diarrhoea was noted with cooked oat hulls included at 2-4% of the diet (Mateos et al., 2006). Effects on digestibility and performance were less notable: the inclusion of 2% cooked oat hulls in low fibre diets improved digestibility in rice-based diets but not in maize-based diets (Mateos et al., 2007).

The inclusion of 10% or 20% of oat mill feed in grower and finisher diets, respectively, had a beneficial effect on the pig health and on the oxidative stability of meat, possibly due to the antioxidant potential of phenolic compounds present in oat by-products. However, the oat mill feed was not as efficient as supplementation with vitamin E (Sobotka et al., 2012). The inclusion of 22% of an unspecified oat by-product also demonstrated antioxidant properties by reducing oxidative stress induced by high-fat diets in pigs (Rezar et al., 2003). Oat "bran" (probably a fibrous by-product rather than actual bran) included at 30% dietary level in finisher diets had detrimental effects on live-weight gain and feed conversion ratio but had no effect on the lean meat and fat content of carcasses and on the proximate chemical composition of meat (Falkowska et al., 2010).

A diet with 5-10% oat hulls given to pigs fed a high maize starch-low protein diet failed to prevent the formation of ulcers (Wesoloski et al., 1975).

Sows

Feeding 300 g/d of oat hulls to preparturient sows decreased the DM content of faeces and the incidence of constipation with positive effects on reproductive performance: low faecal DM was positively correlated with higher biometrical contractions and shorter parturition duration, resulting in fewer stillborn piglets per litter (Beening, 1999).

Oat bran

Sows

Oat bran has been used in sow nutrition experiments to demonstrate the effect of a source of soluble fibre-rich diet on digestibility and reproductive performance. Including oat bran at 30% of the diet increased energy digestibility, but not nitrogen digestibility, as soluble fibre promotes microbial growth and activity and slows intestinal passage rate. This positive effect also increased fermentation of insoluble fibre in the hindgut of the sows (Renteria-Flores et al., 2008a). The oat bran diet had no effect on embryo survival and litter size (Renteria-Flores et al., 2008b).

Poultry 

The nutritive value of oat hulls and oat mill feed for poultry is low due to their content in insoluble fibre. However, the inclusion of a small amount of oat hulls (10%) had beneficial effects on the starch digestibility of the diet, without negative effects on broiler performance (Hetland et al., 2003). The inclusion of 3% oat hulls was also reported to improve performance (Gonzalez Alvarado et al., 2010).

Large amounts of hulls reduced body weight in broiler breeder females and improved satiety and behaviour: diets containing up to 20% of hulls can be an alternative method of feed restriction in poultry (Hocking et al., 2004).

In chickens, protein quality of oat bran is similar to that of dehulled soybean meal (Hahn et al., 1990).

Rabbits 

Oat hulls, as a source of insoluble fibre, are a classic compound feed ingredient in commercial rabbit feeding (Cheeke et al., 1980; Carabaño et al., 1992; Gómez-Conde et al., 2007). The typical inclusion rate is between 5 and 15% (Carabaño et al., 2008), although some studies have included up to 50% oat hulls in rabbit diets without any problem (Spreadbury et al., 1978). The main disadvantage of oat hulls, besides their low energy content, is that their inclusion is detrimental to the quality of feed pellets (Thomas et al., 2001).

Nutritional tables
Tables of chemical composition and nutritional value 

Avg: average or predicted value; SD: standard deviation; Min: minimum value; Max: maximum value; Nb: number of values (samples) used

Main analysis Unit Avg SD Min Max Nb
Dry matter % as fed 90.3 1.1 88.4 92.7 88
Crude protein % DM 5.2 1.5 2.5 8.4 107
Crude fibre % DM 30.6 3.0 25.9 36.1 87
NDF % DM 75.8 8.8 64.2 89.2 49
ADF % DM 36.0 2.1 33.1 41.2 33
Lignin % DM 7.1 1.3 4.8 9.8 54
Ether extract % DM 2.2 0.8 1.0 3.7 51
Ash % DM 4.6 0.9 3.5 7.1 68
Starch (polarimetry) % DM 9.9 4.9 1.5 17.4 46
Total sugars % DM 1.2 0.7 0.5 3.1 15
Gross energy MJ/kg DM 18.4 18.3 18.6 2 *
 
Minerals Unit Avg SD Min Max Nb
Calcium g/kg DM 1.9 1.0 1.0 4.5 13
Phosphorus g/kg DM 1.8 0.8 0.6 3.3 14
Potassium g/kg DM 5.9 1.2 4.6 7.0 3
Sodium g/kg DM 0.1 0.0 0.1 0.1 3
Magnesium g/kg DM 0.6 1
 
Amino acids Unit Avg SD Min Max Nb
Arginine % protein 4.0 1
Cystine % protein 1.5 1
Glycine % protein 4.4 1
Histidine % protein 1.3 1
Isoleucine % protein 3.4 1
Leucine % protein 6.6 1
Lysine % protein 4.0 1
Methionine % protein 1.8 1
Phenylalanine % protein 5.3 1
Threonine % protein 3.3 1
Tryptophan % protein 2.1 1
Tyrosine % protein 2.8 1
Valine % protein 4.8 1
 
Ruminant nutritive values Unit Avg SD Min Max Nb
OM digestibility, Ruminant % 34.8 *
Energy digestibility, ruminants % 32.2 *
DE ruminants MJ/kg DM 5.9 *
ME ruminants MJ/kg DM 4.9 *
 
Pig nutritive values Unit Avg SD Min Max Nb
Energy digestibility, growing pig % 42.1 *
DE growing pig MJ/kg DM 7.8 *
MEn growing pig MJ/kg DM 7.2 *
NE growing pig MJ/kg DM 4.3 *

The asterisk * indicates that the average value was obtained by an equation.

References

AFZ, 2011; Bach Knudsen, 1997; De Vuyst, 1962; Hindrichsen et al., 2004; Hsu et al., 1987; McCarthy et al., 1990; Pereira et al., 1999; Stanogias et al., 1994; Swain et al., 1994; Vargas et al., 1965; Waters et al., 1992; Welch et al., 1983

Last updated on 24/10/2012 00:44:41

Main analysis Unit Avg SD Min Max Nb
Dry matter % as fed 89.9 1.1 87.9 91.7 22
Crude protein % DM 8.2 1.1 6.5 10.5 21
Crude fibre % DM 22.4 2.2 18.2 24.9 22
NDF % DM 55.4 2.4 55.4 61.4 4 *
ADF % DM 27.5 3.7 26.9 35.0 4 *
Lignin % DM 7.1 4.4 4.3 13.6 4
Ether extract % DM 3.8 0.5 2.5 4.7 17
Ash % DM 4.0 0.3 3.5 4.7 18
Starch (polarimetry) % DM 25.0 5.9 16.5 37.1 19
Total sugars % DM 3.9 1.6 1.7 5.6 4
Gross energy MJ/kg DM 18.8 *
 
Minerals Unit Avg SD Min Max Nb
Calcium g/kg DM 1.7 1.2 1.0 3.7 5
Phosphorus g/kg DM 2.9 0.7 2.3 4.1 5
Sodium g/kg DM 0.4 1
Manganese mg/kg DM 58 49 66 2
Zinc mg/kg DM 27 1
 
Amino acids Unit Avg SD Min Max Nb
Arginine % protein 4.1 1
Histidine % protein 1.1 1
Isoleucine % protein 3.4 1
Leucine % protein 5.8 1
Lysine % protein 3.5 1
Methionine % protein 0.4 1
Phenylalanine % protein 2.8 1
Threonine % protein 2.6 1
Tryptophan % protein 0.7 1
Tyrosine % protein 2.8 1
Valine % protein 3.7 1
 
Ruminant nutritive values Unit Avg SD Min Max Nb
OM digestibility, Ruminant % 50.4 *
Energy digestibility, ruminants % 48.2 *
DE ruminants MJ/kg DM 9.0 *
ME ruminants MJ/kg DM 7.4 *
 
Pig nutritive values Unit Avg SD Min Max Nb
Energy digestibility, growing pig % 54.9 *
DE growing pig MJ/kg DM 10.3 *
MEn growing pig MJ/kg DM 9.8 *
NE growing pig MJ/kg DM 6.7 *

The asterisk * indicates that the average value was obtained by an equation.

References

Abrams, 1961; AFZ, 2011; Dewar, 1967; Morgan et al., 1984; Williams, 1955

Last updated on 24/10/2012 00:45:42

Main analysis Unit Avg SD Min Max Nb
Dry matter % as fed 90.6 90.3 90.9 2
Crude protein % DM 19.3 2.0 16.7 22.1 5
Crude fibre % DM 4.0 *
NDF % DM 15.8 10.4 21.3 2
ADF % DM 4.7 4.5 4.9 2
Lignin % DM 2.9 0.5 2.6 3.5 3
Ether extract % DM 7.8 1.5 6.9 9.6 3
Ash % DM 3.3 0.7 2.6 4.2 4
Starch (polarimetry) % DM 48.3 46.6 49.9 2
Total sugars % DM 1.6 1.1 2.0 2
Gross energy MJ/kg DM 19.8 *
 
Minerals Unit Avg SD Min Max Nb
Calcium g/kg DM 1.1 0.8 1.3 2
Phosphorus g/kg DM 6.2 4.5 7.8 2
Potassium g/kg DM 5.8 1
Sodium g/kg DM 0.1 1
Magnesium g/kg DM 2.6 1
 
Amino acids Unit Avg SD Min Max Nb
Alanine % protein 4.3 1
Arginine % protein 6.1 1
Aspartic acid % protein 7.7 1
Cystine % protein 2.9 1
Glutamic acid % protein 19.7 1
Glycine % protein 4.6 1
Histidine % protein 2.2 1
Isoleucine % protein 3.6 1
Leucine % protein 7.2 1
Lysine % protein 3.9 1
Methionine % protein 1.6 1
Phenylalanine % protein 4.8 1
Proline % protein 5.3 1
Serine % protein 4.3 1
Threonine % protein 3.1 1
Tryptophan % protein 1.2 1
Tyrosine % protein 1.9 1
Valine % protein 4.9 1
 
Ruminant nutritive values Unit Avg SD Min Max Nb
OM digestibility, Ruminant % 85.6 *
Energy digestibility, ruminants % 84.4 *
DE ruminants MJ/kg DM 16.7 *
ME ruminants MJ/kg DM 13.7 *
 
Pig nutritive values Unit Avg SD Min Max Nb
Energy digestibility, growing pig % 83.8 *
DE growing pig MJ/kg DM 16.6 *
MEn growing pig MJ/kg DM 15.9 *
NE growing pig MJ/kg DM 12.2 *

The asterisk * indicates that the average value was obtained by an equation.

References

Bach Knudsen et al., 1993; Bach Knudsen et al., 2000; Fadel, 1992; Hahn et al., 1990; Lirette et al., 1993

Last updated on 24/10/2012 00:44:41

References
References 
Datasheet citation 

Heuzé V., Tran G., Chapoutot P., Lessire M., Lebas F., 2016. Oat hulls and oat mill feed. Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. http://www.feedipedia.org/node/707 Last updated on July 20, 2016, 11:05

English correction by Tim Smith (Animal Science consultant) and Hélène Thiollet (AFZ)
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