Die Bodenkultur - Journal for Land Management, Food and Environment
L. Gruber, R. Steinwender, T. Guggenberger, J. Häusler and A. Schauer:
Comparison of organic and conventional farming on a grassland farm
2nd Communication: Feed intake, milk yield, health and fertility parameters
In a grassland farm at BAL Gumpenstein, organic (BE) and conventional farming (KE) were compared in an interdisciplinary experiment lasting 11 years. The experimental groups differed in the treatment of slurry (aeration and addition of rock-meal in BE), the level of fertilization (147 kg/ha mineral N in KE in addition to slurry), in the method of weed control (only mechanical in BE) and the origin of the concentrate for the dairy cows (from organic farms in BE, Table 1). Each experimental group comprised 7 Brown Swiss and Holstein Friesian cows until their withdrawal from the group became neccessary. In that case they were replaced with pregnant heifers or young cows (Table 2). The feed intake was measured in 12 feeding trials (6 in the summer and 6 in the winter period), each lasting 2 to 3 weeks (n = 83 per group). At the same time the digestibility of the individual forages was tested in vivo using 4 wethers each.
The milk yield was determined daily for the whole experimental group and also individually for each cow every 42 days by the official milk recording.
On a DM basis, the forage ration consisted of 95 % fresh grass and 5 % hay in summer and 56 % grass silage and 44 % hay in winter (Table 6). The forage intake was nearly the same in groups BE and KE (13.4 and 13.1 kg DM per cow arid day, Table 5). In total 1,203 and 1,285 kg concentrate were fed per cow per year in groups BE and KE, respectively.
The OM digestibility of the forages did not differ significantly between the experimental groups (65.8 and 64.5 % in hay, 69.3 and 71.8 % in grass silage and 72.2 arid 71.4 % in fresh grass in groups BE and KE, Table 3).
The milk yield per cow and year was identical (5,867 and 5,877 kg ECM in groups BE and KE), however the milk production per unit area was 2,000 kg ECM lower in group BE due to the smaller DM yield of grassland and therefore lower stocking rate per hectare (7,516 and 9,507 kg ECM in BE and KE, Table 7).
There were no significant differences in any of the health parameters (treatment by the veterinary surgeon, reasons for withdrawal of the cows) between the experimental groups (Table 8). However, there was a slight tendency for unfavourable values in group BE (e.g 5.7 and 4.8 treatments by the veterinarian per lactation as well as 28 and 23 % replacements per lactation in groups BE and KE, respectively). In the fertility parameters, group BE was in part significantly lower (2.3 and 1.9 services per conception in BE arid KE, Non Return Rate 29 and 48 %).
From the present results it can be concluded that organic farming on a grassland farm does not lead to differences in the feed value of the forages, feed intake or milk yield, when compared to conventional farming. However, a lower stocking rate per hectare due to lower DM yield of the grassland has to be taken into account. As a consequence milk production per unit area will be reduced.
Key words: Organic farming, grassland farm, feed intake, milk yield, health and fertility parameters.