There are limited data on the average nitrogen (N) intake and N loss for the different classes of equine livestock, and the different equine production systems within New Zealand. Using a deterministic model, the total nitrogen excreted, and nitrogen partitioned into animal requirements, urine and faeces were estimated based on the crude protein requirement, digestible crude protein intake, and crude protein excreted in urine and faeces. Separate models were generated for five different livestock classes managed within three different production systems (commercial breeding farm, sport horse and racehorse). Overall, the N in diet (%), the modelled daily N intake and N losses varied with the percentage of pasture in the diet. The faecal N loss remained consistent (20-25%) across diets and horse classes whereas urinary N loss increased with daily N intake and percentage of pasture in the diet. Total N loss per day was estimated to be 0.18, 0.28, and 0.48 g N/kg body weight in racehorse, sport horse and Thoroughbred mares respectively. The N excretion per unit weight from young horses, racehorses and sport horses were substantially lower than that reported for ruminants. Therefore, horse-specific data should be used when modelling farm-level nitrogen excretion.
Proceedings of the New Zealand Society of Animal Production, Volume 79, Palmerston North, 1-7, 2019
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