Energy uptake and utilization by limit- and ad libitum-fed growing horses.

The study focuses on the differences in growth and feed efficiency between horses that are limit-fed and those allowed to eat freely. It shows that horses who can eat as much as they want gain more weight and grow taller than those whose food is restricted. It also suggests that these horses need more energy in the cold and that existing guidelines for energy needs may be too low.

Research Methodology

• The experiment made use of 18 weanling horses, which were divided into two groups. One group was fed on a limited diet, while the other group was allowed to feed ad libitum, meaning they could eat as much as they wanted.
• The scientists kept track of the horses’ growth and efficiency in converting food into energy (feed utilization) for a total of 78 weeks.

Findings

• The horses fed ad libitum grew 24% larger in terms of weight compared to those on a limited diet.
• Despite different feeding regimes, both groups showed a similar weight distribution along their bodies, with 57% of their total body weight in the front and 43% in their hind.
• In terms of height at the withers (shoulders), the horses allowed to eat freely had a greater net gain and average daily gain (ADG) across the 78-week period than those eating a restricted diet.
• Across three generations of age (6-12, 12-18, and 18-24 months), these horses consumed between 19 to 44% more Digestible Energy (DE) than what the 1978 NRC tables suggested.
• DE intake was positively correlated with the weight of the horse and seemed to be influenced by the barn’s temperature – the colder the temperature, the more energy horses consumed.
• Energy requirements for maintaining body functions (maintenance energy requirements) varied slightly between the two types of feeding, with limit-fed horses requiring a bit more energy.

Implications

• The researchers suggested that guidelines from the NRC might only be suitable to a certain extent. Based on skeletal growth, these guidelines seemed suitable for growth. But in terms of ADG, horses on high-forage diets gained weight at a slower pace than what these guidelines predicted.
• They also found that only 22 to 75% of the values that the NRC tables projected were achieved regarding the amount of weight gain per unit of DE consumed over the maintenance requirement. This indicated that horses might not gain weight as efficiently from their diets as previously assumed.