This study investigates how changes in body weight can affect bone turnover and phosphorus excretion in adult horses. The research compares horses on weight-gaining, weight-maintaining, and weight-losing diet routines, assessing how these varied diets impact bone resorption and formation rates, as well as phosphorus output in feces.

Study Design and Methodology

• The experiment involved fifteen horses with an average weight of 555 ± 8 kg. These were divided into three groups: those designed to lose weight (LO; n = 5), those designed to maintain weight (MA; n = 5), and those designed to gain weight (GA; n = 5).
• The diets for the three groups were controlled so that they had varying amounts of digestible energy – 75% of maintenance requirements for LO, 100% for MA, and 145% for GA. However, the protein and mineral content of the diets remained the same.
• The weight change period lasted 27 ± 6 days. At the end of this period, blood samples were taken from the horses to assess bone biomarkers. Furthermore, a total fecal collection was also conducted over five consecutive days to measure fecal mineral output.

Findings

• Interestingly, there was no significant weight change difference between the horses on the MA diet and those on the GA or LO diets. However, a significant weight change was observed between the GA and LO groups, with respective weight changes of 0.49 kg/d and -1.16 kg/d.
• A negative correlation was found between weight change and cross-linking C-terminal telopeptides of type-I collagen (a marker of bone resorption). This indicates that as weight changed, there was a decrease in the level of these telopeptides, suggesting reduced bone resorption.
• A tendency towards a positive correlation was also found between weight change and bone alkaline phosphatase (a marker of bone formation), implying that weight change could potentially increase bone formation.
• Fecal P output was slightly lower in horses from the GA group than in the LO group, with the MA group showing intermediate and non-significant differences. This suggests that weight loss could result in increased bone resorption, leading to potentially higher phosphorus losses from the body.

Conclusion

• The findings from this study suggest that weight change in horses can significantly influence bone metabolism i.e., bone resorption and formation, as well as the excretion of minerals like phosphorus, thereby highlighting the potential impacts of diet on skeletal health in horses.