Renal energy excretion of horses depends on renal hippuric acid and nitrogen excretion.

The study explores how the dietary intake of horses, particularly differing feeds, impacts renal energy, nitrogen, and hippuric acid excretion. It finds the highest hippuric acid excretion with grass intake and the lowest with soybean meal consumption.

Study Overview

• The study focuses on predicting renal energy excretion, critical in determining the metabolizable energy system for horses.
• The source of the feed, namely fresh grass, grass silage, grass cobs, alfalfa hay, straw, extruded straw and soybean meal, was manipulated to evaluate their effects on renal energy, nitrogen, and hippuric acid excretion.
• Using four adult ponies of varying body weight, the researchers administered these various diets and subsequently analysed the feed, urine, and faeces for three days to measure different parameters.

Key Results

• The researchers observed a correlation between renal energy excretion and renal nitrogen excretion, and hippuric acid excretion. Renal hippuric acid excretion was highest after the intake of fresh grass and lowest after the intake of soybean meal.
• The excretion of hippuric acid per gram of dry matter intake was significantly higher after consuming fresh grass compared to other rations. However, there was no detected relationship between aromatic amino acid intake and renal hippuric acid excretion.

Feed Categorisation

• Based on the study results and existing literature data, feeds were proposed to be categorised into four groups. Each group represented differentiated energy losses per gram crude protein (CP) intake. For instance, protein supplements, including soybean meal, demonstrated 4.2-4.9 kJ/g CP intake energy loss.
• Notably, for the group including hay, preserved grass products, and straw, the researchers spotted a negative relationship between renal energy losses per gram of CP and the content of CP, or neutral-detergent-insoluble CP in dry matter.

Implications

• The research findings offer insights into optimising horse nutrition by understanding how various feed types impact renal energy excretion.
• It also establishes an understanding of how certain feed influences the urinary excretion of hippuric acid, which is a crucial parameter in nutritional adjustment for horses.