6. Own research
6.1 Materials and methods: Foraging (modelling – Paper I)
The objective of paper I was to investigate the technical and environmental performance at farm level of outdoor free-range sows and growing pigs foraging in the range area compared to the current organic production system with sows on grass-clover pastures and growing pigs housed in stables with outdoor access.
The hypotheses:
Improved foraging in the range area will reduce greenhouse gas emissions (GHG) compared to a system with sows and growing pigs foraging on grass-clover and compared to the current Danish organic practice with sows on pasture and growing pigs in stables
Organic production systems with growing pigs in an improved forage crop system will reduce nitrate leaching at farm level compared to a system with growing pigs foraging on grass-clover and improve overall farm environmental performance also compared to the current practice.
Firstly, the technical performance of three scenarios for Danish organic pig production systems was modelled (Figure 6.1). Scenario 1 or the reference scenario represented the current practice with sows on pasture and growing pigs housed in stables (indoor finishing). Scenario 2 and 3 represented the alternative scenarios where sows and growing pigs were foraging in the range area. In scenario 2, pigs were foraging on grass-clover (free-range:
grass-clover), whereas in scenario 3 efforts were done to construct a cropping system that
allowed a maximum intake by foraging considering the type of feed and availability over the year. This scenario included lucerne, Jerusalem artichokes and grass-clover (free-range:
alternative crops)
Figure 6.1. Schematic overview of the issues investigated in paper I: Nitrogen balance at farm level, nitrogen leaching and greenhouse gas emissions modelled in three scenarios of organic pig production.
Technical performance
The technical performance of the three scenarios provided the basis for calculating the environmental performance. The basis of all three scenarios was 100 annual sows with production of 1925 finishers and 84 ha based on a stocking density of 1.4 livestock units ha-1 year-1, corresponding to 140 kg N ha-1.
The sow system was similar in all three scenarios with outdoor free-range pregnant and lactating sows and indoor housing during insemination. Piglets were weaned at seven weeks of age. In the indoor finishing scenario weaners were moved indoors and housed in smaller groups until 30 kg and then moved to larger groups until slaughter at 110 kg. In the two free- range scenarios weaners and growing pigs were housed outdoors in paddocks until slaughter at 110 kg.
In all three scenarios, the crop rotation for sows constituted 36 ha and 48 ha for growing pigs (Table 6.1). In the free-range: alternative crops scenario gilts and pregnant sows had access to Jerusalem artichokes. The size of the paddock area was based on legislation on stocking density according to Danish environmental regulations (2.8 livestock units ha-1 every second year, corresponding to 280 kg N ha-1). Hence for pregnant and lactating sows, a minimum of 10 ha was required.
In the indoor finishing scenario, the oats produced in the crop rotation for sows (12 ha) were allocated to gilts, dry sows and pregnant sows. The crop rotation for growing pigs consisted of 16 ha of barley, 16 ha of peas and 16 ha of barley. The produced barley and peas were
allocated to growing pigs.
In the free-range: grass-clover scenario, half of the crop rotation was cultivated with barley (24 ha) and the other half with grass-clover (24 ha). The growing pigs were foraging on the 24 ha of grass-clover, divided into four paddocks comprising of 6 ha each.
In the free-range: alternative crops scenario, the 48 ha for growing pigs were divided into two crop rotations. One rotation consisted of 30 ha: Lucerne (5 ha), lucerne (5 ha), barley (5), barley (5), Jerusalem artichokes (5) and Jerusalem artichokes (5). The second rotation
comprised 18 ha with 6 ha of barley, followed by 6 ha of grass-clover and after that 6 ha of barley. During winter, growing pigs were supplemented with lucerne silage. In March, April, September, October and November, growing pigs were foraging on Jerusalem artichokes. During May and June, growing pigs were foraging on grass-clover and during July and August on lucerne. In both free-range scenarios, the total production of barley was allocated to the growing pigs.
In all three scenarios, pastures for lactating sows (2.5 ha) were not assumed to contribute in terms of grazing or production of silage. For pregnant sows 2.5 ha of pastures were estimated to produce 18,300 Mega joule (MJ) metabolisable energy (ME) ha-1. Also, the 5 ha grazed after harvest for silage were estimated to produce 18,300 MJ ME ha-1 and the 5 ha for silage 30,500 MJ ME ha-1.
Table 6.1. Production characteristics for three modelled organic pig production systems Sow
herd Growing pigs
Production characteristics: All systems Current practice1 Free-range: grass-clover2 Free-range: alternative crops3 Crop rotation, ha Barley 12 32 24 22 Oats 12 Peas 16 Grass-clover 12 24 6 Lucerne 10 Jerusalem artichokes 10 Total hectares 36 48 48 48 Yield, kg DM ha-1 Barley 3,825 3,825 3,825 3,825 Oats 3,825 Peas 2,556 Grass-clover (thereof grazed) 4,920 (1,630) 4,094 (1,356) 2326 (2,326) Lucerne, (thereof grazed) 6,531 (1,454) Jerusalem artichokes 6,667 Average yield, kg DM ha-1 4,190 3,402 3,960 4,793 1Indoor finishing: Sows on pasture and growing pigs housed in stables with outdoor concrete
areas.
2Free-range: grass-clover: Sows and growing pigs forage in grass-clover paddocks. 3Free-range: alternative crops: Sows and growing pigs forage on grass-clover, lucerne, and
Jerusalem artichokes.
I all three scenarios, sows returned to the same field every third year. In the free-range scenarios with foraging, pigs were moved in the crop rotation throughout the year according to availability of forage crops. To optimize foraging, pigs were subjected to strip-grazing. To get a more precise estimate of the amount of N going into the farming system through the feed in the three scenarios, the nutrient (CP) content in organic feed mixtures available at Danish feed mills was used and not the nutrient requirements. Also, when formulating feed rations, protein sources were based on crops grown in Denmark or Northern Europe as much as possible. Concentrate feed for lactating sows and weaners was purchased as these groups are the most demanding in terms of essential amino-acids. Feed composition was based on Danish norms for conventional pigs in terms of the recommended level of digestible CP per MJ ME.
For sows, the energy consumption was based on norms for conventional sows plus 15% related to thermoregulation and increased activity. For growing pigs, energy and protein consumption was based on norms for conventional pigs. On top of this, for the indoor
finishing scenario, 7% energy was added to meet requirements for thermoregulation and
increased activity.
In the two free-range scenarios, 20% energy was added on top of the norm for conventional pigs to accommodate requirements for thermoregulation and increased activity related to foraging.
In the indoor finishing scenario, growing pigs were allocated roughage corresponding to 3% of the energy content of the daily feed ration. It was assumed that weaners were not able to utilise energy and nutrients in the forage. For non-lactating sows roughage comprised 22% of the energy in the daily feed ration.
For non-lactating sows, in the free-range: grass-clover scenario, 36% of the energy in the daily feed ration consisted of forage, whereas in the free-range: alternative crops scenario, the figure was 60%. For both free-range scenarios, growing pigs (30-50 kg) were estimated to utilise forage corresponding to 3.7 MJ ME kg-1 weight gain (up to 18% on a DM basis) and for finishers (50-110) 8.5 MJ ME kg-1 weight gain (up to 22% on a DM basis), assuming there was no significant impact on daily gain.
Environmental performance
For each of the three scenarios, the environmental performance of the systems was modelled in terms of GHG emissions and N leaching.
Nitrogen balance – potential nitrate leaching
Nitrogen balances were calculated at farm level as the difference between the N input to the system (purchased in feed, straw, seeds, biological N fixation and deposition) and N output from the system (live pigs, culled sows and dead animals). Nitrogen emissions and changes in soil N were deducted from the N surplus to estimate potential N leaching. Calculations of N emissions were based on emission factors from the literature and adjustments to the current systems.
Greenhouse gas emissions
Three categories of GHG emissions were included:
1. Energy use in fields and stables, soil carbon changes, land use changes (LUC): Carbon dioxide (CO2)
2. From feed production: Nitrous oxide (N2O)