Cereal grains

Corn is the most common cereal grain used in swine diets in the United States and many countries around the world. Corn contains relatively greater energy level than other cereal grains due to its high concentration of starch and oil, and low concentration of fiber.

Corn contains approximately 60 to 65% starch (NRC, 2012) with apparent total tract digestibility of around 90 to 96% (Rojas and Stein, 2015). Oil content is around 3.5% and fiber content is less than 10% NDF (NRC, 2012). These characteristics make the energy value of corn relatively greater than other cereal grains.

Crude protein (7 to 9%) and lysine content (0.25%) in corn is less than most other cereal grains (NRC, 2012), but standardized ileal digestibility of amino acids is relatively high, around 75 to 85% (Cervantes-Pahm et al., 2014). Phosphorus content in corn is approximately 0.25%, but standardized total tract digestibility of phosphorus is only 25 to 30% because at least 2/3 of the phosphorus is bound to phytate. The addition of exogenous phytase is a common practice in corn-based diets to increase phosphorus digestibility to around 45 to 60% (Almeida and Stein, 2012).

Improvements in genetic selection and modification have resulted in some corn varieties with enhanced nutrient profiles for use in swine diets. These corn varieties include nutrient dense, high oil, high lysine, and low phytate corn. However, the market availability of these corn varieties is typically limited.

Milo or sorghum is grown for human consumption, livestock feeding, and ethanol production in many countries around the world. Milo is an excellent energy source and can replace all or part of the corn in swine diets (Stein et al., 2016).

The concentration of starch and fiber in milo is very similar to that in corn, but milo contains slightly less oil than corn which results in an energy content of 98 to 99% relative to that of corn (Goodband et al., 2016). Because of this, pigs fed milo-based diets generally have similar growth rate but slightly poorer feed efficiency as those fed corn-based diets. A strategy that can improve feed efficiency and relative feeding value of milo to corn is fine grinding (Paulk et al., 2015).

Crude protein (9%) and lysine content (0.20%) are similar to corn (NRC, 2012). The concentration of some other amino acids, particularly threonine, tryptophan, and valine, is greater in milo compared to corn (Goodband et al., 2016), but standardized ileal digestibility of amino acids is slightly lower in milo than corn, around 70 to 75% (Cervantes-Pahm et al., 2014). The use of feed-grade amino acids allows to balance for amino acids while lowering the amount of soybean meal or other protein sources in milo-based diets. While generally not a concern in milo grown in the United States, the presence of tannins in milo must be considered, as tannins in concentrations greater than 1% negatively affect digestibility of amino acids (Stein et al., 2016).

Milo contains more saturated fatty acids and less polyunsaturated fatty acids than corn (Goodband et al., 2016). This characteristic may improve pork fat quality and decrease carcass iodine value and might allow for greater inclusion of co-products high in polyunsaturated fatty acids, such as distillers dried grains with solubles, compared to corn-based diets.

Wheat is the traditional source of energy in swine diets in Canada, Europe, and Australia. Wheat is an excellent feed grain for swine, but usually is not competitively priced with corn in the United States. Wheat can replace all or part of the corn in swine diets without affecting growth performance (Stein et al., 2016).

The concentration of starch and fiber in wheat is similar to that in corn, but wheat contains significantly less oil (1.8%) than corn (NRC, 2012) which results in an energy content of 91 to 97% relative to that of corn (Stein et al., 2010).

Crude protein (14%) and amino acid content, particularly lysine (0.40%), threonine, and tryptophan, are greater in wheat than in corn (NRC, 2012; Rosenfelder et al., 2013). The standardized ileal digestibility of amino acids is relatively high and similar to that in corn, around 75 to 85% (Cervantes-Pahm et al., 2014). These characteristics reduce the amount of soybean meal or other protein sources and feed-grade amino acids in wheat-based diets. Phosphorus concentration and availability in wheat is greater than in corn due to the presence of endogenous phytase that improves phosphorus digestibility (Rosenfelder et al., 2013).

Based on the greater concentration of amino acids and phosphorus, wheat is generally given a relative feeding value greater than that of corn (approximately 105 to 110% of corn), but the energy content of wheat needs to be accounted for in wheat-based diets.

Wheat tends to flour when finely ground, which may reduce feed intake and increase the risk on gastric lesions. Thus, wheat should be coarsely ground to an average particle size of 600 mm (Stein et al., 2010).

Barley is grown mainly for malting or livestock feeding in the United States, Canada, Europe, and Australia. The nutrient composition varies among hulled and dehulled barley grains.

Barley contains lower concentration of starch (50%) and oil (2%) and greater concentration of fiber (18% NDF) compared to corn (NRC, 2012), which results in lower relative feeding value than that of corn (approximately 90 to 95% of corn) (Stein et al., 2016). However, there is significant variability in fiber concentration in barley varieties and, therefore, the replacement of corn by barley may not reduce growth performance under all circumstances (Woyengo et al., 2014).

Barley fiber is more fermentable than fiber from corn. The greater content of soluble fiber in barley increases hindgut fermentation and may improve gut health, but may also reduce feed intake and feces consistency in pigs (Wang et al., 2018).

Crude protein (11%) and lysine content (0.40%) are greater in barley than in corn (NRC, 2012), and standardized ileal digestibility of amino acids is similar to that in corn, around 75 to 85% (Cervantes-Pahm et al., 2014).

Oats is mainly grown for human consumption and only smaller quantities are used for livestock feeding.

Oats contains lower concentration of starch (39%) and greater concentration of oil (5%) compared to corn (NRC, 2012). The concentration of fiber (25% NDF) in oats is greater than that of corn or any other cereal grain (NRC, 2012).

Crude protein (11%) and lysine content (0.5%) are greater in oats than in corn. Oat protein contains a favorable amino acid profile and greater standardized amino acid digestibility compared to corn or any other cereal grain, around 80 to 90% (Cervantes-Pahm et al., 2014).

Although the amino acid profile is favorable, the high fiber content limits the application of oats in swine diets (Stein et al., 2016). Oats are most commonly included in initial nursery diets because the greater content of insoluble fiber may improve gut health and reduce post-weaning diarrhea in weanling pigs. Oats may also be included in gestation diets for sows.