Technical information - nutrition

Fast and Slow Grains



by Alex Ashwood

BRAHMAN NEWS SEPTEMBER 2007 Issue #156

The properties and benefits of different types of processed grains have received increasing interest of nutritionists and beef producers.

Recently grains have been categorised as “fast” or “slow” grains depending on the site and rate of digestion. Sorghum and maize are slow grains and barley and wheat are fast grains.

The rumen digestion of grains can vary from 70% for grains such as wheat and barley to 40% for maize and sorghum depending on a number of factors.

The type and level of processing and level of feeding can modify the passage and rate of starch digestion of fast and slow grains.

Although the nutritional value and energy cost of particular grain (see articles in Brahman News Sept, 2000) are the key criteria when selecting a grain, the properties of processed grain are important to beef producers feeding high grain-low roughage rations to cattle.

Maize grain (13-14 MJ ME/KG DM)

The nutritional value of corn grain (maize) are shown in Table 1. The crude protein (CP) content can vary considerably depending on the fertiliser practices and environmental conditions.

Table 1: Maize grain nutrient values (DM basis)

Component Feedstuffs NRC
1997 1996
Crude protein % 9.2 9.8∀1.06
Calcium % 0.2 0.3∀0.07
Phosphorus % 0.29 0.32∀0.04
Potassium % 0.35 0.44∀0.06
Copper ppm 3.5 2.51∀1.98
Manganese ppm 7.0 7.89∀7.1
Zinc ppm 17.4 24.2∀11.1

As with all grains, the calcium content of maize grain is low but the phosphorus and potassium levels are quite high. The trace minerals (ie copper, zinc and manganese) differ between grain sources although their bioavailability is quite high due to the low fibre content of maize grain.

The relatively high net energy value of corn is further increased by processing. Grinding or rolling whole maize grain reduces visible grain fragments in the dung increasing the rate of digestion in the rumen. The finer the grain particles, however, increases the incidence of acidosis and rumen disfunction. It is suggested for optimal health and feed intake maize grain should be coarsely ground in low roughage diets.

Steam flaking of maize grain increases the energy value by 15 per cent compared to rolled maize grain. This is attributed to increased ruminal starch digestion. The finer the flake, the greater the digestion which can lead to metabolic disorders due to explosive starch digestion. Coarser flakes result in higher feed intakes and reduced health problems. Whole grain, obviously has the lowest energy value since the starch in the intact kernels is not readily digested despite increased chewing and regurgitation of whole grains.

Sorghum grain (9-13 MJ ME/kg DM)

The nutritional values of sorghum are shown in Table 2. Variations in nutritional values are greater for sorghum than maize grain due to the wider range of environments in which sorghum is grown.

Despite generally higher protein and lower energy values sorghum diets result in lower ruminal concentrations of ammonia. It is suggested that the lower protein availability may reduce the starch digestibility of the sorghum.

Differences in the energy value of sorghum and maize can be reduced by processing. Steam flaked sorghum has the same energy value as dry milled corn. Steam flaked sorghum has a 20% higher NE value than dry rolled sorghum.

Table 2: Sorghum grain nutrient values (DM basis)

Component Feedstuffs NRC
1997 1996
Crude protein % 12.4 12.6∀1.99
Calcium % 0.04 0.04∀0.04
Phosphorus % 0.33 0.34∀0.07
Potassium % 0.38 0.44∀0.11
Copper ppm 15.8 4.7∀1.9
Manganese ppm 14.5 15.4∀4.6
Zinc ppm 15.4 16-19

Sorghum has a higher fibre (NDF) level than maize grain and the coat of the intact seed inhibits water penetration and grain digestibility.

A problem with mechanical processing is the mixed and varied particle size of sorghum. Nevertheless, studies have shown that cattle fed high grain-low roughage diets perform better with rolled than ground sorghum.

Barley Grain (12-13.5 MJ ME/kg DM)

The nutritional values of barley are shown in Table 3. Barley generally has a higher protein content than maize and sorghum grains. The starch in barley is more loosely bound and subsequently starch digestion is greater - it is a “fast” grain. The concentrations of most minerals in barley tend to be greater due to the higher fibre content of barley.

Starch in barley is readily digested in rolled grain. Despite the high digestibility of rolled barley studies show that steam flaking improves the energy value by 8 per cent.

Table 3: Barley grain nutrient values (DM basis)

Component Feedstuffs NRC
1997 1996
Crude protein % 11.6-12.9 13.2∀1.50
Calcium % 0.04-0.09 0.05∀0.03
Phosphorus % 0.38-0.47 0.35∀0.05
Potassium % 0.62 0.57∀0.18
Copper ppm 8.8 0.53∀2.8
Manganese ppm 10.0 18.3∀8.5
Zinc ppm 22.34 13.0∀5.03

Wheat Grain (12-13.5 MJ ME/kg DM)

The nutritional values of wheat grain are shown in Table 4. Wheat has the highest levels of protein. Replacing some of the sorghum and maize grain in a ration with wheat can reduce the level of supplemented protein. Like all grains, however, the protein levels in wheat are variable.

Table 4: Wheat grain nutrient values (DM basis)

Component Feedstuffs NRC
1997 1996
Crude protein % 12.6-15.0 14.2∀1.96
Calcium % 0.06 0.05∀0.03
Phosphorus % 0.35-4.0 0.44∀0.14
Potassium % 0.47-5.0 0.40∀0.02
Copper ppm 11-12 6.48∀1.3
Manganese ppm 35-45 36.6∀2.4
Zinc ppm 32-39 38.1∀2.8

Wheat is also higher in minerals, particularly copper and manganese than other grains. Wheat starch in rolled grain is readily digested and wheat is an extremely “fast” grain. High intakes of wheat can result is acidosis (ie. Grain sickness). The economic benefits of steam flaking (6%) are doubtful.

Processing grains

The effectiveness of grains depends on the nutritional value and degree of processing. The benefits of processing are most noticeable in high grain-low roughage diets with slow grains more responsive to processing than fast grains.

The effect of processing on stock performance also depends on a number of factors such as the age of stock, the type and level of roughage fed to stock and health safety factors.

As with all high grain diets, particularly fast grains and highly processed slow grains changes in rations need to be gradual using an “introductory” grain feed schedule and the appropriate buffers are recommended.

Bottom Line

The benefits of processing “fast” or “slow” grains depends on the need, the cost of processing and the level of feeding. All grains except oats require some form of processing but the degree of processing depends on:

  • the expected improvements to the meat:grain ratios (ie. kg weight gain to kg grain fed responses)
  • the cost of processing
  • the availability of grains
  • the level of grain in the diet
  • the amount of fibre in the diet
  • target weight gains