The nutritional quality of wheat or barley can vary substantially (see previous Centre of Swine Volume 10 Number 3). Ignoring the existing variation may cause lower finished feed quality and thereby impact the swine producer economically through reduced growth performance.

For wheat and barley, reduced nutritional quality usually means a reduced digestible energy (DE) content. The reduction in DE content is almost completely caused by a reduction in energy digestibility, not by a reduction in the total amount of energy in the ingredient sample (or gross energy = GE content). The reduction in energy digestibility is usually related to an increase in fibre content of the grain.

Solutions for the use of low quality grains in diet formulations while maintaining growth performance should focus on two aspects: (1) correcting diet formulations to achieve the formulated diet DE content or (2) enzyme supplementation or feed processing to overcome to reduction in energy digestibility of the grain. For either solution, correct prediction of DE content of individual wheat and barley samples may be critical, but the impact of correct prediction of DE content on further decision making regarding enzyme supplementation or feed processing to improve energy digestibility is poorly understood. Equations to predict DE content of wheat and barley are presently being evaluated using the 2002-harvest.

To study whether a specific wheat sample would impact the beneficial effects of enzyme supplementation or feed processing, three samples of wheat were collected from the 2002-harvest. The three wheat samples (W1, W2, and W3) had a similar content of crude protein (18.8 to 19.7% DM) but had a wide range in neutral detergent fibre (NDF) content (W1, 20.1; W2, 29.3; and W3, 35.7% DM).

Results of a digestibility study with grower pigs indicate that the increased fibre content for samples W1 to W3 indeed resulted in decreased energy digestibility (Figure 1) and reduced DE content from 3,680 to 3,320 kcal/kg DM, confirming the importance of ingredient evaluation and that an increase in fibre (NDF) coincides with a decrease in energy digestibility and DE content. The range in wheat DE content also reflects a range in economic value of more than $15 per tonne of wheat used for swine feed.

Wheat diets were supplemented with a carbohydrase enzyme (xylanase). The enzyme should help the pig to digest energy, because negative effects of fibre fractions (or arabinoxylans) on energy digestibility will be alleviated. Indeed, enzyme supplementation improved energy digestibility for wheat samples W2 and W3, but not for wheat sample W1 (Figure 2), indicating that the beneficial effect of enzymes is dependent on the wheat sample in the diet. This result further stresses the importance of ingredient evaluation, or the importance of enzyme supplementation to alleviated expected differences in energy digestibility. The underlying reason for the positive response for W2 and W3 to enzyme supplementation and the lack thereof for W1 will be related to the content of fibre fractions in the wheat, specifically the fraction called xylan. Therefore, the wheat samples are presently being analysed for these fractions to further related wheat characteristics to prediction of an enzyme response.

Wheat samples were ground across three hammer mill screens to achieve a predicted particle size of 900, 650, and 400 mm (microns). Particle size reduction should help the pig to digest energy, because a finer particle size means that the ratio of surface area to volume of the particles is increased. In other words, digestive enzymes of the pig or microbes of the pig have better access to the nutrients with a finer particle size. Indeed, enzyme supplementation improved energy digestibility for wheat samples W2 and W3, but not for wheat sample W1 (Figure 3), indicating that the beneficial effect of particle size reduction is dependent on the wheat sample in the diet.