Effects of a protein deficient diet and urea supplementation on lactating mares

Six lactating mares were fed either a low protein diet or the same diet with added urea ad libitum over 71 days. The quantity consumed by the mares, milk intakes of their foals, milk composition, plasma urea nitrogen (PUN), mare liveweight changes and foal growth rates were measured. The mares were unable to consume sufficient quantities of either diet to meet their nitrogen requirements and all lost weight. Adding urea to the diet significantly increased PUN in mares and foals, raised urea concentrations in the milk, decreased the mares' feed intake and significantly increased their weight loss. Low concentrations of protein were measured in milk from mares on both diets. Milk intakes of all the foals were reduced and they showed poor growth rates.