Wheat bran is a co-product of the flour industry obtained during the milling process of cereal grains, mainly soft wheat (Triticum aestivum) and durum wheat (Triticum durum). It essentially consists of the fraction that, after being separated from the flour, includes the outer layers (cuticle, pericarp, and seed coat) mixed with varying amounts of floury endosperm.

Although it is one of the most widely used ingredients for swine feed with different interests and features depending on the physiological phase and the level of inclusion used (palatability, nutrient supply, bulking, water retention, regulation of intestinal passage, fermentation, microbiota regulation, etc.), it is important to point out that it is very difficult to establish a precise and universal definition.

This is mainly due to the processing done in the flour mill (type of milling, winnowing, and classification of fractions) and to the contamination with bran from other cereal grains which, due to the difficulty of management, end up mixed and marketed as wheat bran (the most common are rye, triticale, barley, and even oats). In the past, and on a small scale, a wide range of co-products were marketed separately, clearly separated by fractions (thick bran, fine bran, medium, second clear, thirds, middlings of different qualities) but today, at the industrial level, due to the difference in origins and types of processing, apart from wheat bran that it is used for human food, and it follows a different quality and marketing characterization, the rest of the fractions are marketed mixed in variable proportions.

Consequently, the fibrous fractions coming from the flour industry have a very variable fiber:starch ratio, from coarse fibrous bran to starchy flours, with very different implications in their incorporation in a formulation, which requires very precise quality control, chemical profiling, and classification upon receipt at the factory.

Comparative study of nutritional values

The systems used in the comparison are: FEDNA (Spain), CVB (the Netherlands), INRA (France), NRC (United States), and Brasil (Brazil).

The FEDNA and CVB evaluation systems present the range of values (minimum and maximum); these come from integrating the different classifications considered by these evaluation systems, based basically on the starch content, which differs basically by the type of processing and recovery system or mixture of fractions categorized as bran and the residual amount of fibrous fraction, with CVB having the largest number of product categories associated with these variables.

2The INRA evaluation system considers only one classification based on the type or variety of the original wheat, differentiating only between soft and durum wheat and considers only one quality as an average value based on the type of wheat, but not on the process.

3For the NRC and BRASIL evaluation systems, only the mean value is presented since both evaluation systems only consider one category or quality of ingredient as the mean value.

It is interesting to note that, despite the great variability, FEDNA and CVB are the systems that consider the widest range of classifications according to the fiber:starch ratio. INRA basically focuses on the origin or variety of wheat used, distinguishing between soft wheat and durum wheat bran, but considers an average value for each of them for characterization and nutritional quality, similar to NRC and BRASIL which, perhaps due to lower use or consumption, only consider one average value for all bran.

For the present review, the maximum and minimum values provided in the tables of the evaluation systems have been considered for the categories of wheat co-products consistent with bran and fine bran (again highlighting the great variability).

As a fibrous ingredient, logically, most of its nutritional characteristics revolve around fiber content and its characteristics. The type of processing and efficiency of the starch extraction system and the final blending with other fractions or origins determine the fiber and starch content. Ratios between fiber and starch content range from 0.3 to 1. Ratios below 0.5 usually indicate that the residual starch concentration is >20% (values between 12.6 and 29.6% have been observed). Associated with the residual starch content, a positive relationship with the EN value is observed for both piglets and adult pigs (R2 >0.70), with this relationship being clearly negative in the case of fiber (R2 =-0.79 and -0.56 for piglets and adult pigs). This explains the differences observed in terms of net energy (NE), where BRASIL, NRC, and CVB (ratios <0.5) in their high starch range present higher NE values than the rest of the evaluation systems (ratios >0.5) (>230 kcal/kg on average). The EN values for the rest of the systems, FEDNA, INRA, and CVB (in their different evaluation ranges), is clearly dependent on the observed ratio between fiber and similar starch and clearly dependent on the amount of residual starch, indicating a clear inversely proportional relationship between the ratio and the EN value (R2 >0.85).

Fat content ranges from 2.9 to 4.7%, being one of the parameters clearly determined by the level of fiber, with an inversely proportional relationship (R2 =0.46) that explains ~15% of the variation in energy. The most extreme values (>4.4) are observed for NRC and INRA (durum wheat) and the lowest values for CVB, FEDNA, and BRASIL.

However, the protein content is very stable (between 14.6 and 15.4%, with the exception of CVB, which gives a lower protein value in one of its categories) and presents little range of variation (<5%). Basically, with the exception of BRASIL, NRC, and CVB (in its category with the lowest ratio), which gives a protein digestibility coefficient lower than the average (-20%), the rest of the FEDNA, CVB, and INRA systems present very similar digestibility coefficients among them (between 62 and 68%), although, with the exception of CVB (high fiber:starch ratio), an inversely proportional response is observed between the fiber:starch ratios and the protein digestibility coefficients (R2 >0.50), indicating the negative impact of fiber-bound protein on its digestibility. In terms of total amino acids, taking lysine and total sulfur as the majority, it can be observed that there are no major differences between the different evaluation systems, although in terms digestibility, CVB presents values 12 and 6% higher for lysine and total sulfur for the category with the highest starch content (similar case for the rest of AA).

Recent findings

1. Net energy of oat bran, wheat bran, and palm kernel expellers fed to growing pigs using indirect calorimetry.

The aim of the experiment was to determine the effects of increasing fiber in diets on heat production and determine the net energy (NE) of oat bran (OB), wheat bran (WB), and palm kernel expellers (PKE) fed to growing pigs using indirect calorimetry (IC). The ATTD of neutral detergent fiber (NDF) was lower (p < 0.01) in pigs fed the WB diet compared with those fed the basal, OB, or PKE diets. The ATTD of ether extract (EE) in pigs fed the PKE diet was greater (p < 0.01) compared with those fed the other diets. The NE contents of OB, WB, and PKE were 10.93, 7.47, and 8.71 MJ/kg DM, respectively.

2. Wheat bran reduces concentrations of digestible, metabolizable, and net energy in diets fed to pigs, but energy values in wheat bran determined by the difference procedure are not different from values estimated from a linear regression procedure.

The effects on DE, ME, and NE for growing pigs of adding 15 or 30% wheat bran to a corn-soybean meal diet were evaluated and compared to values calculated using the difference procedure with values obtained using linear regression. After conducting the study it was concluded that increasing the inclusion of wheat bran in a corn-soybean meal based diet reduced energy and nutrient digestibility and heat production as well as DE, ME, and NE of diets, but values for DE, ME, and NE for wheat bran determined using the difference procedure were not different from values determined using linear regression.

3. Wheat bran and oat hulls have dose-dependent effects on ad-libitum feed intake in pigs related to digesta hydration and colonic fermentation.

Five levels of wheat-bran (WB) or oat-hulls (OH) were added to a highly digestible starch-based diet fed to pigs ad-libitum to study functional and physiological effects of fiber inclusion and type. Overall, WB diets showed 8-11% lower ADFI than OH diets. WB diets produced over 20% more Short Chain Fatty Acids (SCFA) than OH or Control diets. WB at 25% produced 22% more SCFA than any other diet. Diets with WB at 25 and 35%, showed higher hydration capacity than any other diet. With increasing levels of OH, intake of base diet was 7% more than control at 5% OH, but 8% less than control at 20% OH. With increasing WB content, intake of base diet decreased. It was concluded that initial increase in passage rate and feed intake at low concentrations of non-swelling fibres; a depression in FI from high fibre bulk; and reduced feed intake from stimulation of ileal and colonic brakes.

4. Effects of dietary fibre level and body weight of pigs on nutrient digestibility and available energy in high-fibre diet based on wheat bran or sunflower meal.

The objectives of the present work were (a) to investigate the effect of body weight (BW) on available energy in fibre-rich diets containing two NDF levels; and (b) to evaluate the effect of fibre type and NDF level on AA digestibility. The concentration of DE, ME and ATTD of GE, CP, NDF and ADF in diets was greate when fed to 90 kg pigs compared with 30 kg pigs. The ME in ingredients was not affected by BW. The ATTD of NDF was negatively correlated with the CF (r = -.98), ADF (r = -.99) and ADL content (r = -.96). The ME of diets was negatively correlated with the ATTD of CF (r = -.98). The addition of SFM increased the standardized ileal digestibility (SID) of Met. Therefore, it is concluded that diets rich in fibre had different nutritional values at different pig weight stages. The AA digestibility depends mainly on chemical composition of diets.

5. Varying dietary levels of wheat pollard and wheat bran in growing pigs: effect on growth and carcass traits.

The present study was conducted to evaluate the effect of increasing levels of wheat pollard as a replacement for wheat bran on growth and carcass characteristics of growing pigs. Significant differences in the rate of gain and efficiency of feed utilisation among treatments were reported. Diet significantly affected weights of the liver, lungs and small intestine. The availability of nutrients was not a limiting factor for the growing pigs and substituting wheat bran for wheat pollard at 60 % improved the pig’s average daily gain and feed efficiency.

Pig333 | David Solà-Oriol | February 23