Trace mineral status and toxic metal accumulation in extensive and intensive pigs in NW Spain
Introduction
Intensive production systems have been designed to achieve a very high productivity at relatively low cost. Animals are maintained at very controlled conditions, including nutrition, to ensure minimum fatalities and increased productivity. From a mineral nutrition point of view, and in order to avoid mineral deficiencies, mineral supplements are incorporated into concentrate feed at concentrations exceeding the physiological requirements; this is possible because there are quite large “safety margins” to avoid mineral toxicity, even though toxic effects can appear when given at supra-optimal concentrations. In relatively unpolluted rural areas, mineral supplements represent an important (or even the main) source of essential trace elements in the diet (Suttle, 2010). However, mineral supplements generally contain higher toxic metal concentrations than most feedstuffs (López-Alonso and Miranda, 2011) although, because of its low rate of inclusion in the concentrate feed their contribution to the total dietary metal exposure is low and toxic metal residues in meat and meat products (mainly offal) are generally below the maximum admissible levels established by the EU (for review see López-Alonso et al., 2007).
However, intensive production systems are highly questioned because of animal welfare and environmental contamination: thousand of animals grow up highly confined and producing an extraordinary large amount of waste. In this context, excess of Cu given to pigs as a growth promoter in the mineral supplement is considered one of the main environmental problems in agricultural land. Excess of dietary Cu (up to 90%) that is not absorbed by the animal is excreted into the faeces, producing Cu-enriched manures (Jondreville et al., 2003) and when spread in the agricultural soils leading to increased soil Cu concentrations (Bengtsson et al., 2003, Poulsen, 1998), toxic effects in plants and microorganisms (Coppenet et al., 1993) and other livestock species (López-Alonso et al., 2000, López-Alonso et al., 2006, Miranda et al., 2006).
In contrast, in extensive low-input production systems, where most or even all animal feed is from the own farm and animals hardly or do not receive mineral supplements, mineral deficiencies or mineral imbalances can appear, especially in places where mineral content in the soil is low or shows a low availability (Mateos et al., 2006, Kumaresan et al., 2009). However, where animals are outdoors, toxic metal (but also essential trace element if present at high concentrations in soil) exposure through soil ingestion by foraging could be higher than through the diet. Information on toxic metal exposure through soil ingestion in pigs is not available in the literature, but results of a recent study in beef cattle in NW Spain indicate that toxic metal accumulation in animal tissues is directly related to grazing activity, which is a reflection of soil ingestion when grazing (Blanco-Penedo, 2008). Because the great rooting activity of pigs, particularly when animals are not fitted with nose rings, soil ingestion can be very high (from 19 to 94%; Rivera-Ferre et al., 2001) compared to ruminants (up to 18%; Thornton and Abrahams, 1983) and the effect of soil ingestion on toxic metal residues in tissues could be very important.
In Galicia (NW Spain) most pig production corresponds to intensive indoor industrial farming feed a highly standardised and balanced concentrate diet. However, in the last years there has been an increase in breeding of the Celta pig, an autochthonous breed maintained on local resources on an extensive silvopastoril system. The Celta pig was the traditional breed on farms until the middle of the 20th century – when it suffered an important recession by the introduction of improved breeds in industrial systems – and its new increase is motivated by the consumer demand of animal welfare and environmentally friendly production systems, together with its highly appreciated organoleptic characteristics (Franco et al., 2006).
The aim of the present study was to determine trace element status and toxic metal accumulation in extensive and intensive pigs in NW Spain.
Section snippets
Farms of study
Three representative extensive and intensive farms were selected for this study in the region of Galicia (NW Spain). All farms were located in rural areas with no identifiable source of anthropogenic metal contamination.
Basically, extensive pig farms (regulated by Real Decreto, 1221/2009 on 4th August) were Celta pig farms maintained on native extensive silvopastoral systems. Animals were outdoors at a maximum density of 2.4 LSU/ha. Animal feed was mainly based on the own-farm resources:
Results and discussion
Trace element concentrations in tissues (liver, kidney and muscle) of extensive and intensive pigs in our study are shown in Table 2. In terms of overall trace metal nutrition, trace element concentrations in the liver (the tissue that best indicates the animal mineral status) are generally within the adequate ranges for this species (Cu: 5–100, Fe: 100–200, Mn: 2.3–4.0, Mo: 0.8–1.9, Se: 0.2–1.2, Zn: 40–90 mg/kg wet weight; Puls, 1994, Suttle, 2010) and are also within the range of trace
Conclusion
The results of our study indicate and appropriate mineral status in both extensive and intensive pigs in NW Spain, even though hepatic mineral concentrations were generally higher in the intensive pigs possibly reflecting mineral supplementation in the concentrate feed. The statistically significantly higher As, Hg and Pb residues as well as the better Fe and Ni status in extensive pigs could be related at least in part with soil ingestion when rooting. On the contrary, the higher Cd
Conflict of interest statement
None of the authors have financial, personal or other relationships with other people or organizations within three years from the beginning of the submitted work that could inappropriately influence, or be perceived to influence, their work.
Acknowledgements
This study was supported by the Xunta de Galicia (Spain) (PGIDT02RA6261001PR).
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