Phosphorus balance and fecal losses in growing Standardbred horses in training fed forage-only diets.

The research studies the effects of high and low phosphorus diets on Standardbred horses in training. Specifically, the study looked at the balance of phosphorus in the animals’ systems and the amount of phosphorus lost through feces.

Research Methodology

The researchers carried out their study using fourteen standardbred horses, with an age average of about 20 months. The horses were adapted to a diet of grass forage containing 0.25% P or phosphorus. In the study, the scientists used two dietary treatments – high phosphorus diet (referred to as high-P) and low phosphorus diet (referred to as low-P) for six days.

• Horses’ daily intake and refusals of food were weighed to monitor consumption.
• Twice daily on days 4 to 6, spot samples of feces were collected and analyzed for total phosphorus and soluble, inorganic phosphorus (Pi).
• To estimate total fecal output, they used acid-insoluble ash as a marker.
• Urinal samples of the horses were collected once from day 4 to 6, for phosphorus and creatinine analysis.

Research Findings

The findings showed that the high-P diet resulted to a greater intake of phosphorus per day (32.0 ± 0.6 g) compared to the low-P diet (17.5 ± 0.6 g), with individual intake ranging from 13.3 to 38.4 g per day. The excretion of phosphorus through feces was also markedly higher for the high-P diet (30.3 ± 0.8 g/day) than the low-P diet. In contrast, phosphorus excretion through urine was under 0.2 g/day for both diets.

Phosphorus Retention and Loss

Using the simple regression analysis model, the researchers estimated the daily endogenous (internal) losses of phosphorus through feces to be less than 10 mg/kg of body weight. Phosphorus retention in the horse’s body was higher for the high-P diet (1.6 ± 0.6) compared to the low-P diet.

Moreover, the study found a strong relationship between the intake of phosphorus and the amount of phosphorus excreted in the feces. Over 80% of the total phosphorus seemed to be soluble and the endogenous losses of phosphorus through feces were similar to those previously reported in horses.

Conclusion

The research concluded that a significant retention of phosphorus occurred in the horses consuming the forage-only diet with a daily phosphorus intake of 7.1 g/100 kg of body weight. It was found that phosphorus is mainly excreted through feces and both total and Pi (soluble, inorganic phosphorus) excretion had a strong relationship with the phosphorus intake.