Published data on livestock and pasture management on Thoroughbred breeding stud farms were collated to model and estimate farm-level variables required to estimate nitrogen leaching. On commercial farms, stocking density doubled during the breeding season (August – December). The effective stocking density increased with farm scale (number of resident mares) but decreased with farm size (total effective area). Therefore, farm nitrogen output may fluctuate seasonally and will be influenced by farm size and scale. Farm size and scale independently affected the stocking and grazing management (i.e., paddock rotation interval) for the different equine stock classes (empty, pregnant, mares with foals). Stocking and grazing management influenced the pasture available and subsequently, the grazing behaviour as determined by the difference between pasture mass of lawns and roughs. The difference between pasture mass of lawns and roughs was reduced with increasing stocking density and decreasing pasture availability, and increased under conditions of high stocking density (>2 mares/ha) and low pasture availability (<400 kg DM/ha/horse). Modification of grazing behaviour could affect the nitrogen-leaching potential by modifying the size of manure-deposition area and the N-loading rate on urine and dung patches. The complex relationship between farm, horse and management factors needs to be included when estimating nitrogen leached from equine properties.

YY, Chin, PJ Back, EK Gee, and CW Rogers

New Zealand Journal of Animal Science and Production, Volume 79, Palmerston North, 65-70, 2019
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