Analysis and simulation modelling of the production in Danish organic and conventional dairy herds

Case studies, descriptive statistics and modelling by simulation based on detailed documentation from commercial farms were used to obtain knowledge about organic as opposed to conventional livestock farming systems. Data from intensive observations over a 3-year period in 13 organic and 18 conventional commercial farms with dairy production as their main enterprise were used in the analysis. Herd structure, like age of cows and replacement ratel was independent of the farming system. In the organic system, milk peak yield per :lactation was lower, but persistently higher, leading to only marginal differences, in annual herd production. A higher amount of roughage in the feed ration reduced the feed intake in early lactation in the organic herd, but a more even intake through lactation could explain the higher persistency in milk production. Feed intake and production results in the two farming systems where simulated with a herd model. The higher amount of roughage, combined with a longer period on pasture and a lower frequency of mastitis in the organic system, could explain the difference between the two systems. It was concluded that if changes in land use and feed supply were the only results of organic farming, feed intake will be reduced, leading to a lower milk production and live weight gain. If conversion to organic farming is followed by a greater attention to pasture management and preventive mastitis control, then our results also show that the effect on feed intake and production will be reduced. (C) 1998 Elsevier Science B.V. All rights reserved.