Introduction

The quantity and quality of feed offered to livestock has a significant impact on livestock productivity, growth and reproductive performance. Balanced feeding programs supply all essential nutrients at or above required levels and at the same time avoid unnecessary overfeeding of any nutrient(s). Large quantities of energy are required to maximize livestock performance. For this reason, energy is often the most expensive nutrient in livestock rations.

The nutrient content of feedstuffs is extremely variable. To properly balance rations, it is critical to determine the nutritional profile of all feed ingredients through feed analysis. This should include an accurate estimate of energy content.

The total quantity of energy contained by a feedstuff can be separated into several different compartments based on how it is used by the consuming animal. The net energy (NE) system measures the quantity of energy available to the animal to manufacture animal products (milk, meat, etc.). The efficiency of energy utilization is influenced by the product being manufactured (maintenance, growth, lactation, pregnancy, etc.). To account for these different efficiencies, the net energy system assigns different energy values to the same feedstuff depending on how the energy is used by the animal. Net energy available for maintenance of body functions is called NE_m, net energy available for growth is designated NE_g and the net energy available for lactation is termed NE_l. When balancing rations, it is important to match the units in which the requirements are expressed with the reported value for the feedstuff, e.g., use the NE_g values of feeds to meet NE_g requirement of animal.

Feed energy content is not usually measured directly. Rather, fibre levels are used to estimate the energy content of feedstuffs; specifically, acid detergent fibre (ADF). Different equations are used to predict energy levels for the various types of forage. To obtain an accurate energy estimate for feed ingredients, it is important that the sample be correctly identified. Equations used to estimate NE_l, NE_g, NE_m content of forages are listed below for your information.

Until recently, the P.E.I. Soil and Feed Laboratory have been reporting only the NE_l value of forages. However, due to requests for NE_g and NE_m values from our clients, these energy values will be reported starting in March of 1996.

Estimating Net Energy Content of Forages

Grasses (Dry Matter Basis)

• NE_L= 2.45 - (0.032 x ADF) Maximum = 1.60
• NE_g= 2.108 - (0.038 x ADF) Maximum = 1.10
• NE_m= NEg + 0.7 Maximum = 1.80

Legumes (Dry Matter Basis)

• NE_L= 2.09 - (0.022 x ADF)Maximum = 1.50
• NE_g= 1.332 - (0.019 x ADF)Maximum = 0.82
• NE_m= NE_g + 0.7 Maximum = 1.52

Mixed Forages (Dry Matter Basis)

• NE_L= 2.30 - (0.028 x ADF)Maximum = 1.55
• NE_g= 1.531 - (0.025 x ADF)Maximum = 0.86
• NE_m= NEg + 0.7 Maximum = 1.56

Corn Silage (Dry Matter Basis)

• NE_L= 2.25 - (0.024 x ADF)Maximum = 1.75
• NE_g= 1.119 - (0.008 x ADF)Maximum = 0.95
• NE_m= NE_g + 0.7 Maximum = 1.65

Grains - Barley, Wheat and Corn (Dry Matter Basis)

• NE_L= 2.15 - (0.028 x ADF)Maximum = 1.75
• NE_g= 0.039 - (0.008 x ADF)Maximum = 0.95
• NE_m= NE_g + 0.7 Maximum = 1.65

For further information contact Brian Douglas at the Soil and Feed Testing Laboratory or your local Agricultural District Office of the P.E.I. Department of Agriculture and Forestry.