@article {3672,
	title = {Simulating the intake and nitrogen excretion from cows grazing forages fertilised with increasing rates of nitrogen},
	journal = {New Zealand Journal of Animal Science and Production},
	volume = {78},
	year = {2018},
	month = {07/2018},
	pages = {141-145},
	address = {Lincoln},
	abstract = {The dry matter intake (DMI), production, and urinary nitrogen (N) excretion of dairy cows grazing forage grown under increasing
N fertiliser rates were explored using a mechanistic model of a grazing ruminant. The MINDY cow model was initialised to
represent a multiparous Holstein-Friesian dairy cow in late lactation (age 3.5 years, 212 days in milk). Simulated cows were
offered a common allowance (30 kg DM/cow/d) of chicory, plantain, lucerne, or perennial ryegrass, fertilised at rates of 0, 100,
200, 350 and 500 kg N/ha/y (0N, 100N etc.) for 20 days in March. Forage physical and chemical composition data were obtained
from a Waikato experimental field site. When N rate increased from 0{\textendash}500N, predicted DMI of cows grazing plantain and ryegrass
increased by 5.2 and 2.7 kg DM/cow/day (43 and 20\% increase), respectively, facilitated by increased sward height and mass, and
reduced herbage strength. Predicted DMI of cows grazing chicory peaked at 200N and, for cows grazing lucerne, declined with
N fertilisation. Intake of highly fertilised (>200N) chicory and lucerne diets were potentially affected by high herbage soluble N
content resulting in high predicted rumen ammonia concentrations (>18 mmol/L), reducing incentive for grazing. While predicted
milk production from cows grazing chicory, plantain and ryegrass increased, the efficiency of dietary N used for milk production
declined, with increasing N applied. Increasing N rate also increased predicted urine N concentration, and urinary N excretion
from simulated cows fed chicory, plantain, and ryegrass. This study suggests that N fertiliser rates of 200N for chicory, plantain
and ryegrass provides a balance between cow production and N excretion.},
	issn = {1176-5283},
	author = {Minnee EMK and Bryant RH and Chapman DF and Gregorini P}
}
