A mathematical model of pasture contamination by grazing cattle and the effects on herbage intake

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Abstract
SUMMARY A mathematical model has been constructed to simulate pasture contamination by the faeces of grazing cattle and the effects on herbage intake. The model describes the rate of deposition of faeces in relation to herbage intake, the effects of contamination on intake as modified by grazing pressure, and the rate at which the influence of faeces on grazing behaviour declines after deposition. The information available on these processes is incomplete and imprecise in a number of respects. It appears from the modelling exercise that further data are most urgently needed on the rate at which the inhibitory influence of faeces declines, and on the precise effect of grazing pressure on the amount of herbage rejected. A secondary effect of contamination is recognized, in which the utilization of herbage initially rejected because of the presence of faeces is modified subsequently because the temporary protection from grazing allows it to become too mature. This effect may be quantitatively larger than the primary contamination effect on untrimmed pastures, but its accurate prediction depends on the establishment of comprehensive relationships between the amount and composition of herbage on offer and intake by the grazing animal. The latter studies deserve at least an equal research priority, in relation to the contamination problem in toto, as the elucidation of the details of the primary effect.