Summary

A co-extruded flaxseed:field pea product was fed to growing pigs for 4, 8 or 12 weeks to determine which combination of duration of feeding and dietary level would provide optimal enrichment of the backfat with 18:3 n-3 (an omega-3 fatty acid). The inclusion of 15 per cent flaxseed in the diet decreased feed intake; there was no effect on average daily gain, and feed efficiency was improved. If 2.5 grams of backfat was incorporated into a serving (100 g) of processed pork, then feeding 10 per cent flaxseed for eight weeks or 15 per cent for 12 weeks would achieve the n-3 fatty acid levels required for an enrichment claim in Canada.

Introduction

Flaxseed is the richest oilseed source of 18:3 n-3 (omega-3) fatty acids and feeding flaxseed to pigs has been used to increase the levels of n-3 fatty acids in pork. Consuming n-3 fatty acids may provide health benefits by reducing the risk factors for several diseases. Thacker, Racz and Soita (2004) from the University of Saskatchewan reported that feeding flax co-extruded with field peas (LinPro, O&T Farms, Regina, SK) could avoid the grinding and storage problems which occur with flaxseed, also a collaborative study with PSCI and the University of Alberta optimised the extrusion conditions for 18:3 availability in pigs.

* “Feeding a co-extruded flaxseed: pea mixture can be used to optimize enrichments of n-3 fatty acids in the back fat of pigs”

Incorporation rates of 18:3 n-3 into pork fat with flaxseed feeding have been variable. Therefore the overall objectives of this study was to feed a flaxseed:field pea blend (LinPro®; O&T Farms, Regina, SK) extruded using conditions which optimized 18:3 availability for various durations and at different levels in the diet to determine which provided optimal and consistent elevated 18:3 n-3 levels in pork fat.

Materials and Methods

Four barrows and four gilts, with an initial body weight of 31 ± 3 kg were randomly assigned to one of ten dietary treatments. Treatments were 3 levels of extruded flaxseed (5, 10 and 15 per cent; Table 1) and 3 durations of feeding (4, 8 and 12 weeks) arranged as a 3 × 3 factorial, plus a control (0 per cent flaxseed). Diets were formulated and adjusted every four weeks to meet the nutrient requirements of the growing pig. Field peas were added to the diets at a constant level to compensate for the peas in the co-extruded product. Tallow was used to balance energy levels among diets within phases. A backfat biopsy was collected from each pig the day prior to slaughter and analyzed for fatty acid concentrations.

Results and Discussion

The inclusion of up to 30 per cent (15 per cent flaxseed) of a co-extruded flaxseed:pea mixture for 12 weeks in the diet of growing pigs had only modest effects on performance (Table 2). Feed intake decreased from 2.60 to 2.47 kg/d (P<0.01; Table 2) but ADG was unaffected (P=0.40) and therefore feed conversion improved (P=0.01) as the amount of flaxseed in the diet increased from five to 15 per cent. Feed intake on the control diet was similar to the 15 per cent flaxseed diet; there is no obvious explanation for this.

Backfat obtained from gilts had less saturated fatty acids and more n-6 fatty acids (P<0.04; data not shown), however the differences between genders is small and probably of limited practical significance. Both the amount of flaxseed in the diet and duration of feeding impacted fatty acid composition of the backfat. Increasing flaxseed in the diet resulted in increases in the percentage of n-3 fatty acids in backfat, including 18:3 (Figure 1A), 20:3, 20:5 n-3, and 22:5 n-3.

Although, not as dramatic, the proportion of n-6 fatty acids also increased (Figure 1B) due to increases in 18:2 n-6 (P<0.01) and 20:2 n-6 (P<0.05). Conversely 20:4 n-6 declined from about 0.19 per cent to 0.12 per cent as the flaxseed concentration of the diet increased from five to 15 per cent. As the level of flaxseed in the diet increased, the percentage of 18:2 n-6 fatty acids decreased, however, because of the greater amount of fat in the diets with added flaxseed the absolute amount of 18:2 n-6 consumed increased, leading to the enrichment of these fatty acids in the backfat.

Overall, the ratio of n-3/n-6 fatty acids in backfat increased (Figure 1C; P<0.05). Generally, when five per cent flaxseed was included in the diet, a plateau in total n-3 fatty acids was observed if it was fed for longer than eight weeks. Conversely, when the diet contained 10 or 15 per cent flaxseed, the level of n-3 fatty acids did not plateau and continued to increase between eight and 12 weeks (P<0.01). The consistent production of pork with enriched levels of n-3 fatty requires a balance between high levels of flax for short durations, which provides efficient rates of deposition, and feeding higher levels for longer durations, which allows for a more consistent rate of deposition.

The Canadian government requires 300 mg n-3 fatty acids per 100 g serving for an enrichment claim. In the present study, 2.5 g of backfat from pigs fed 10 per cent flaxseed for eight weeks or 15 per cent for 12 weeks would achieve the n-3 fatty acid levels for a claim. Additionally, if 15 per cent flaxseed was fed for 12 weeks, 2.0 g of backfat would achieve the required levels of n-3 fatty acids (assuming 85 per cent fat in backfat). The backfat could potentially be used to manufacture pork products enriched in n-3 fatty acids.

Additionally, commercial lean meat from pigs fed flax co-extruded with field peas would probably have sufficient fat (subcutaneous, inter- and intramuscular) in retail cuts to achieve the required enrichment levels.

Conclusion

Feeding flax co-extruded with field peas can be used to optimise consistent enrichments of n-3 fatty acids in back fat of pigs. Relatively small amounts of this fat used to manufacture pork products would be required to meet the Canadian standard for a n-3 enrichment claim.

Acknowledgment

Strategic program funding was provided by Sask Pork, Alberta Pork, Manitoba Pork Council and Saskatchewan Agriculture and Food Development Fund. Specific funding for this project was provided by Vandeputte s. a., Belgium.

April 2010