What the hay: predicting equine voluntary forage intake using a meta-analysis approach.

The research investigates how to predict how much forage horses will eat voluntarily. By analyzing data from 61 previous studies, it develops equations that predict forage intake based on factors such as the horse’s size, the quality of the forage, and whether the horse has access to pasture.

Introduction and Problem Statement

• The ability to accurately estimate equine feed intake is important for diet formulation because it determines the amount of nutrients the animal receives.
• Inaccurate intake estimates can result in underfeeding or overfeeding, leading to nutritional imbalances.
• Individual variations in how much forage a horse consumes are well-known, but no comprehensive equations exist to predict these variations based on both animal and forage factors.
• The study aims to consolidate current knowledge on voluntary forage dry matter intake (VFDMI) in horses and use a meta-analysis to develop predictive equations for forage intake.

Methods

• A systematic literature search identified 61 studies that met the criteria for inclusion in the meta-analysis.
• From each study, data were extracted on:
  • Forage intake outcomes (in kg/day and in g/kg of body weight)
  • Diet composition (forage type and nutrient composition)
  • Animal factors (sex, age, breed, body weight, exercise level)
• Two outcome variables were studied:
  • VFDMI in kilograms per day (kg/d)
  • VFDMI in grams per kilogram of body weight (g/kg BW)
• Linear mixed models were used to analyze the data, treating each study as a random effect, and a backward-stepping approach was applied to identify key variables where P < 0.1.

Key Findings

• Several factors were found to influence VFDMI in both kg/d and g/kg BW, including:
  • Forage quality (measured by neutral detergent fiber and crude protein content)
  • Forage type (grass, legume, or mixed forage)
  • The size of the animal (horses versus ponies)
  • Management factors like pasture access
• Higher-quality forages, which have lower neutral detergent fiber and higher crude protein content, led to increased forage intake due to better digestibility.
• Forage intake increased as body weight increased, but ponies consumed more forage per kilogram of body weight compared to horses.
• Pasture access (grazing) reduced forage intake compared to stalled animals, possibly because grazing takes longer than eating hay or other stored forages.

Conclusion and Implications

• The study developed predictive equations with high accuracy and precision for equine VFDMI (concordance correlation coefficient = 0.82–0.95; root mean squared error = 0.82–5.49).
• These equations can be useful for equine nutritionists, owners, and managers to ensure horses are receiving appropriate nutrient levels through their forage intake.
• The study confirms that animal traits (such as size) and forage quality are critical in determining how much forage horses will consume voluntarily, which should be considered when formulating diets.