Nutrient utilization by limit- and ad libitum-fed growing horses.

The article investigates how limited and unrestricted (ad libitum) feeding affects the nutrient absorption in young, growing horses. It shows that, while the energy digestibility is not substantially affected by feed intake amounts in horses aged 6 to 12 months, unrestricted feeding resulted in higher nutrient absorption in horses aged between 12 and 24 months.

Experimental Design and Procedure

• This research involved 18 weanling colts, from Quarter Horse and Paint breeds, which were divided into two groups based on the feeding method – limited and ad libitum (as much as they wanted).
• The digestibility of the nutrients was evaluated across three different stages of the horses’ development – between 6 and 12 months, 12 and 18 months, and 18 and 24 months.

Findings and Results

• In the first stage (6-12 months), the level of feed intake did not significantly affect the energy digestibility, which was between 64% to 68%.
• However, in the 12-24 months stage, ad libitum-fed horses showed 9-10% greater energy digestibility than those fed limitly. The difference, though, was mitigated upon adjusting for Dry Matter (DM) intake.
• The efficiency in energy use was similar between limit-fed mature ponies and growing horses from 6 to 18 months. However, by 24 months, the mature ponies used the digested dietary energy more efficiently than the young horses.
• Horses fed ad libitum digested more dietary protein as compared to horses fed limitly, but this difference disappeared when adjusted for Dry Matter intake.
• The true digestibilities of dietary calcium (Ca) were estimated at a range of 71% to 42% across the periods, while that of phosphorus (P) ranged from 52% to 6%.
• All horses absorbed enough phosphorus between 6 and 18 months, but by 24 months, the horses were in negative phosphorus balance despite an adequate intake.
• Using regression analyses, the researchers predicted the daily endogenous fecal calcium and phosphorus to be 36 and 18 mg/kg body weight respectively.

Implications of the Study

• This study provides valuable insights on optimal feeding strategies for growing horses, indicating that the nutrient and energy utilization varies with age and feeding amounts.
• The results may guide horse caregivers, revealing that unrestricted feeding can possibly enhance nutrient absorption during certain developmental stages.
• It establishes the need to adjust diet compositions over time, particularly with nutrients such as phosphorus, to prevent deficiencies.