The effect of diet composition on the digestibility and fecal excretion of trace minerals in horses

This study investigates the correlation between dietary intake of these trace minerals and their fecal excretion rates, aiming to enhance our understanding of equine mineral metabolism and improve dietary recommendations. The criteria for selection included healthy horses aged 4 to 14, weighing 400 to 600 kg, with a good body condition score (BCS, 3/5) across 14 yards in the Netherlands. Data on yard type, size, and location, as well as horse demographics (age, sex, breed, weight), were collected. Each horse’s diet was analyzed concerning daily nutritional intake and requirements according to National Research Council (NRC). Fecal samples were randomly collected from stables (n=14) for dietary analysis and stored in three labeled jars. Samples, approximately 200 g each, were frozen at -20°C and later analyzed for cobalt (Co), copper (Cu), manganese (Mn), and zinc (Zn) using inductively coupled plasma mass spectroscopy (ICP-MS). Among the 14 horses, all were geldings, with one being a cold blood and another a Welsh pony, while the rest were warmbloods. Their median age was 10 years, mean body weight (BW) 506 ± 82.3 kg. Most horses grazed, averaging 8.6 ± 8.5 h/day. All received commercial concentrate feed, with nine also receiving supplements. Energy intakes varied, with ten horses consuming more than required. Trace mineral intake was classified by the NRC; two horses had high Cu intake. Manganese intake exceeded NRC recommendations significantly (618.6 ± 125.1 mg vs. 1403.8 ± 312.7 mg), while Co intake was 2.3 ± 1.6 mg against a requirement of 0.8 ± 0.2 mg. Manganese excretion in feces was highest (459.1 ± 386.4 mg/day), followed by Zn (58.3 ± 46.0 mg), Cu (2.7 ± 3.2 mg), and Co (1.5 ± 0.4 mg). This study emphasizes the need for tailored diets to prevent excess mineral intake in horses, which mainly originates from concentrate feed and supplements. Further research with a larger sample size is necessary for a deeper understanding.