The kind of feeds used has a role in urine volume. The forages fed are typically mature grass or cereal straws. It has been indicated by a number of researchers that horses fed a grass hay in comparison to a legume forage will consistently produce lower levels or urine. Cuddeford et al 1992, and Fonnesbeck 1968 suggest that the difference in urine volume is due to the effect the fibre components of the forage have on fecal moisture. The fecal residue attracts water and reduces water reabsorption from the hindgut.
Fecal moisture is higher on horses fed grass hays compared to legume hays.
Protein level has been suggested as a factor in urine volume. Cymbaluk et al 1988 noted that there was a positive correlation between protein level on urine volume. Experience suggests that there are a number of factors which affect urine volume particularly fibre components, protein and possibly minerals such as potassium. Mares must be fed properly to meet their nutrient requirements. Producers can use nutrition to maximize estrogen production by feeding the mare to meet her requirements, and having the mare in optimum body condition at breeding time so that a large percentage of the mares become pregnant early in the breeding season.