A mechanistic and dynamic model of a grazing ruminant, MINDY, was used to explore the effect of both the proportion dietary inclusion of plantain (PL) and its grazing management, compared with ryegrass (RG), on urinary N (UN) excretion of dairy cows. The treatment tested were: 1) frequency of allocation and 2) dietary proportion of PL. Frequency of allocation was set by stripgrazing (24 hrs. pasture breaks) PL or RG monocultures for 1, 5 or 10 consecutive days, allocated either after the morning (AM) or afternoon (PM) milking. The proportion of dietary PL was set by offering either 25 or 50% of the diet as PL monocultures allocated either AM or PM. MINDY had greater intake of PL-containing diets than RG alone, resulting in increased N intake. However, with the exception of the ‘frequency’ treatments, daily urinary N excretion (UN) was reduced by including PL compared with RG alone. Plantain monocultures led to similar or lower urine volume compared with RG. Grazing RG and PL every 1 or 5 days increased urine volume, frequency and UN compared with RG or continuous PL. Offering PL or RG in the AM compared with PM reduced UN but reduced milk yield. This modelling exercise suggests that including PL in cattle’s diet reduces UN and UN concentration, and that the frequency and timing of its allocation help to reduce environmental impact further while maintaining or increasing MS.
Proceedings of the New Zealand Society of Animal Production, Volume 78, Lincoln, 151-156, 2018
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