The development of a metabolizable energy system for horses.

The research article describes the development of a new system for calculating metabolizable energy (ME) in horses. The study involves revisiting predictive equations for gross energy and digestible energy (DE) while considering renal energy losses related to feed protein content and methane energy losses related to feed fibre content.

Understanding Metabolizable Energy

• Metabolizable energy (ME) is the amount of energy available from food after subtracting the energy losses in digestive, metabolic and urinary processes.
• The study aims to establish a reliable system that predicts a horse’s ME based on the type of feed it consumes.
• Part of this research involved analyzing past studies on the relationship between the type of feed and energy losses.

Insights into Energy Losses in Horses

• In horses, renal (urinary) energy losses are greater than losses through methane production.
• They found that these renal losses were more closely associated with total protein intake than with digestible protein intake.
• The reason for this could be that for every gram of digestible crude protein, energy losses may be more for roughages (fodder) than for concentrates.
• However, protein digestibility is lower in forages than in concentrates. The summed outcome is a consistent urinary energy loss of 0.008 MJ per gram of crude protein in the feed.

Methane Energy Losses in Horses

• The study found that horses lose less energy as methane compared to ruminants (cud-chewing animals). This is likely due to hindgut fermentation processes in horses which lead to reductive acidogenesis, rather than methanogenesis.
• Methane energy losses in horses are closely linked to the intake of crude fibre. On average, the loss is 0.002 MJ ME per gram of crude fibre.

Calculating Metabolizable Energy

• The researchers developed an equation to calculate ME from any predictive equation for DE (Digestible Energy).
• The ME is the DE, less a quantity based on the crude protein and less a quantity based on the crude fibre. The formula is as follows: ME MJ/kg = DE MJ/kg – 0.008 MJ/g crude protein – 0.002 MJ/g crude fibre.
• In effect, this research provides a more nuanced and accurate way of calculating the metabolizable energy in horse feed, which can aid in effective feed utilization and improved horse health.