۱- Introduction

۲- Materials and methods

۳- Results

۴- Discussion

۵- Conclusions

References

Abstract

The objective of this paper was to examine how cutting frequency, silage fermentation patterns and clover performance in grass–clover swards influence the use of inputs and profitability in an organic dairy system. A linear programming model was developed to compare a three-cut and a two-cut system for a model farm in Central Norway, either with restricted or extensive silage fermentation at low or high red clover (Trifolium pratense L.) proportion in the sward, giving 8 different silage types in all. Input-output relations incorporated into the model were derived from a meta-analysis of organic grassland field trials in Norway as well as a silage fermentation experiment, and with feed intakes and milk yields from simulations with the ‘TINE Optifôr’ feed ration planner in the Norfor feed evaluation system. The model maximized total gross margin of farms with 260,000 l milk quota and housing capacity for 45 cows, with separate model versions for each of the 8 silage types. Farmland availability varied from 30 to 70 ha with 40 ha as the basis. Our results suggested that farmland availability and marginal return of a competing barley crop profoundly influenced the profitability of the different silage types. A high clover proportion increased dry matter (DM) yields and was far more important for profitability than the score on the other factors considered at restricted land availabilities. Profits with the three-cut systems were always greater than those with the two-cut systems, the former being associated with greater silage intakes and improved dairy cow performances but lower DM forage yields. Three-cut systems were further favoured as land availability increased and also by a lower marginal return of barley. Although use of an acidifying silage additive improved feed intakes and milk production per cow, the practice reduced total milk production and depressed profit compared to untreated, extensively fermented silage at restrictive land availabilities. With more land available, and in particular at a low marginal return of barley, use of a silage additive was profitable.

Introduction

At high latitudes, the grazing season is short, and dairy farmers need to feed cows indoors for up to 8–۹ months, resulting in a major reliance on conserved forage crops and concentrates. These limitations result in higher input costs than in pasture-based systems and a need, also for organic farmers, to lean somewhat towards high input-output milk production systems. Such strategies require highly digestible forages and rather high proportions of concentrates in the diet. The annual energy corrected milk (ECM) yield per cow in organic production in Norway increased from 6045 kg in 2007 to 7179 kg in 2013. In the same period, concentrate feeding increased from 153 to 177 MJ Net energy lactation per 100 kg ECM produced. Although the proportion of concentrate in the diet has increased considerably, the average organic dairy ration is still predominantly forage-based. Of the total net energy intake in 2012, 41% was made up of grass–clover silage and 11% of pasture (TINE Rådgivning, 2014). Feed is generally the greatest expense for milk production and various practices in the production of forages and feeding of the herd need to be evaluated to improve profits of organic dairy systems. The ban of synthetic nitrogen fertilisers makes legumes crucial for forage yield and quality and for profits in organic systems (Doyle and Topp, 2004). In mixed grass–clover swards cropped for silage production, the regrowths contain more clover than the spring growth (Steinshamn et al., 2016). The regrowth herbage has, therefore, usually higher crude protein (CP) concentration and lower energy value than the herbage from the first cut.