Full or Partial Outdoor Rearing of Slaughter Pigs – Effects on Performance, Carcass Quality and Nutrient Load

An experiment with slaughter pigs from weaning to slaughter including five treatments and five replicates was carried out at the Danish organic experimental station, Rugballegård. Treatments included full or partial outdoor rearing of the pigs, and the replicates covered the seasonal effects. Pigs fed ad libitum indoors had a significantly lower feed consumption (5 MJ ME /kg gain), a lower lean percentage (2.3% points), and a higher backfat depth (1.1 mm, P < 0.05) than pigs fed ad libitum outdoors. Compared with outdoor pigs fed ad libitum, restricted feeding outdoors resulted in a significantly lower daily gain (107 g), a lower feed consumption (6.3 MJ ME/kg gain), higher lean percentage (2.1% points), and a reduced backfat (1.8 mm) (P <0.001). The content of soil nitrogen was considerably higher than for the soil outside the paddocks. Despite a considerable variation within the paddocks, N was distributed throughout the paddock. The present investigation highlights the fact that outdoor rearing of organic finishers may be a competitive option even in a temperate climate and all year round. Introduction In many countries, including Denmark, organic pork production takes place in barns where the pigs have free access to a limited outdoor area. However, such housing is often very expensive and it may be questioned whether pigs reared under such conditions comply with consumer expectations of organic farming. Alternatively, slaughter pigs can be reared outdoors. However, data on production results obtained from outdoor rearing are limited. In addition, in relation to the deposition of manure in the outdoor paddocks, outdoor rearing may have drawbacks such as an increased risk of nitrate leaching. Strategies that combine indoor and outdoor rearing may be preferable from an overall perspective. The purposes of this investigation were to quantify differences in performance and carcass quality traits of pigs reared outdoors or indoors, and to highlight the risk of N-leaching from grass paddocks in such systems. Methodology The experimental design comprised five rearing strategies in five replicates using a group size of ten pigs that were balanced in terms of live weight and sex. Upon weaning at age 7-8 weeks (approx. 19 kg live weight) piglets born in an outdoor system were distributed over the five rearing strategies as follows: 1. Piglets were moved indoors at weaning and fed ad libitum until slaughter. 2. Piglets stayed on pasture and were fed restrictively with concentrates until 40 kg live weight, followed by ad libitum feeding in an indoor pen. 3. Piglets stayed on pasture and were fed restrictively with concentrates until 80 kg live weight, followed by ad libitum feeding in an indoor pen. 4. Piglets stayed on pasture until slaughter and were fed restrictively during the whole period. 5. As treatment 4, but the growers were fed ad libitum until slaughter. The first replicate started in January 2002 and the fifth and last replicate was completed in April 2003, so that the seasonal variation was covered by the design. C:\Dokumente und Einstellungen\Jens Unrath\Desktop\Jasmin\Orgprints\ISOFAR\4368-Hermansen_etal_4p_revised-ed.doc In the field each experimental unit (group of ten pigs) was allocated to a ‘new’ piece of land, differing in size according to the expected nutrient load from the pigs. The stocking rate in the field was calculated to cause a level of excretion of 280 kg N per hectare. To ensure a good distribution of the manure and thereby the environmental load from the pigs on the pasture, the huts, troughs and water supply were moved on a regular basis. All pigs were individually weighed at weaning, at transfer, and at slaughter. Soil samples where collected and grass cover evaluated each time pigs were transferred from the field to housing or slaughterhouse. Grid points were established for every 5x5 m in the 10 m wide paddocks and similarly points were established outside the paddocks for every 5 m as a reference. At each point soil samples were collected to 40 cm by pooling 8 soil cores. A total of 948 soil samples have been analysed for content of mineral N, exchangeable K and extractable P to determine the level and the distribution of nutrients within the paddocks. Results The content of soil nitrogen was considerably higher than for the soil outside the paddocks. Despite considerable variation within the paddocks, increased N levels were found throughout the paddock (Figure 1). Generally, it was difficult to maintain a grass cover in the paddocks. The nitrogen use efficiency in the paddocks (feed N input relative to animal N output) decreased the longer pigs were kept on the pasture. Thus, N in piglets kept outside until 40 kg accounted for 38% of feed N input, whereas N in piglets on pasture until slaughter accounted for only 30% of feed N input. 100 kg/ha 200 300 N-min 0-40 cm Col 17 vs Col 18 Col 45 vs Col 46 Col 47 vs Col 48 Distance (m) 0 25 50 75 100 40 kg