When a horse transitions from timed feeding to 24/7 free-choice forage, significant changes occur at the cellular, metabolic, and hormonal levels, which can initially result in weight gain.
Here’s what happens:
1. Cellular and Metabolic Changes
Metabolic Programming: Restricted feeding causes the horse's body to anticipate periods of scarcity, priming cells to store energy as fat. This response, known as "metabolic preparedness," ensures survival but becomes counterproductive when forage becomes unlimited (Getty, 2017).
Caloric Overshoot: Initially, horses may overeat due to a psychological response to previous food restrictions. This caloric intake often exceeds their immediate energy needs, contributing to weight gain during the adjustment period (EquiMed, 2017).
Shift to Continuous Digestion: Horses' digestive systems are designed to process small amounts of forage continuously. Restricted feeding disrupts this natural flow, and transitioning back to free-choice forage takes time for the gut microbiom to adjust fully (Getty, 2017).
2. Hormonal Adjustments
Cortisol and Stress: Horses on restricted diets exhibit elevated cortisol levels, a stress hormone linked to fat storage. Transitioning to free-choice forage reduces this stress response, although fat stores may persist initially as the body adjusts (Getty, 2017).
Insulin and Fat Storage: Fluctuations in blood sugar caused by timed feeding schedules can impair insulin sensitivity, leading to fat accumulation. Free-choice forage helps stabilize blood sugar and insulin levels, but these effects may take weeks or months to normalize (EquiMed, 2017).
Leptin and Ghrelin: Restricted feeding disrupts the balance between leptin (satiety hormone) and ghrelin (hunger hormone). While free-choice forage reduces ghrelin production, leptin regulation takes longer to align, leading to temporary overeating (Getty, 2017).
3. Psychological and Behavioral Factors
Horses transitioning from restricted feeding often overconsume initially due to the "feast" response. Over time, they begin to trust that food is always available, reducing anxiety and leading to self-regulation of intake. This process can take weeks or months, depending on the horse's history and the quality of the forage (EquiMed, 2017).
How to Support a Healthy Transition
Gradual Increase: Slowly increase access to free-choice forage to allow metabolic and hormonal adaptation.
Low-Sugar Forage: Use hay with a non-structural carbohydrate (NSC) level below 12% and Digestible Energy below 0.88 Mcal/lb to prevent excessive calorie intake (Getty, 2017).
Use Slow Feeders: These can help regulate consumption without frustrating the horse, which could increase cortisol (EquiMed, 2017).
Encourage Movement: Exercise promotes calorie expenditure, improves metabolic rate, and reduces insulin resistance (EquiMed, 2017).
Takeaway
Weight gain during the transition to free-choice forage is a normal and temporary adaptation. With proper management, the benefits—reduced stress, improved digestion, and stabilized metabolism—far outweigh the initial challenges.
References:
Getty, J. M. (2017). Free-choice forage feeding: Beyond the basics. Retrieved from Getty Equine Nutrition.
EquiMed. (2017). My horse eats free-choice hay, but she is getting fat. Retrieved from EquiMed - Horse Health Matters.
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