Omega-3 fatty acids in pig nutrition: implications for zootechnical performances, carcass and fat quality

The extent of incorporation of dietary alpha-linolenic acid -readily available in linseed- in pig diets, in view of repercussions on zootechnical performance, carcass and fat quality of pigs, is investigated. Ninety hybrid pigs (Piétrain x Seghers hybrid cross, 41 barrows and 49 gilts), divided in three comparable groups, were fed ad libitum three experimental diets, containing respectively 4 g, 7 g and 10 g alpha-linolenic acid per kg feed, originating from linseed. The increase of polyunsaturated fatty acid content in the feed (11.9 g, 15.2 g and 18.8 g per kg feed, resp.) could almost be completely attributed to the variation in alpha-linolenic acid. Despite several anti-nutritional factors, present in linseed, zootechnical performance was not affected by the diet. However, carcass quality, in terms of lean meat % and conformation, was less favourable for the highest linseed level compared to the intermediate level. Loin fat thickness was not influenced by the fat source in the diet. More pronounced was the effect of sex on zootechnical and carcass parameters: gilts showed a lower feed intake and weight gain, resulting in a more favourable feed conversion ratio, a thinner backfat layer, a higher meat content and a superior conformation, compared to the barrows. The linolenic acid content in the backfat increased from 3.1 g to 6.8 g per 100 g of total fatty acids for the barrows and from 3.4 g to 7.0 g per 100 g of total fatty acids for the gilts. A significant positive correlation was found between the live weight at slaughter and C16:0 and C18:0 content in the backfat; C18:2 and C20:4 content, on the contrary, were negatively correlated with the live weight at slaughter. A more unsaturated fatty acid pattern of the backfat, as a result of higher C18:3 levels in the feed, resulted in higher TBA-values (thiobarbituric acid), without occurrence, though, of off-odours during the fat thawing. Thus PUFA content in the backfat reached a maximum of respectively 18 g and 19 g per 100 g of total fatty acids for the barrows and the gilts, without implications for the consistency of the fat.