Nutritional value of oilseed rape and its co-products for pig and poultry feed: potential improvements and implications for plant breeders

Abstract

Oilseed rape (OSR) produces a seed with high energy content, and rape meal, its co-product following oil extraction, is a valuable mid-protein animal feed. Both rape seed and meal have value in poultry diets, but at present only rape meal is used in pig diets. This review considers the potential for improving the nutritional value of OSR seed and meal for non-ruminants, and seeks to inform plant breeders about potential targets for variety development for the feed market. Four key elements were considered: (1) A literature search focusing on the limiting factors affecting utilisation of OSR seed and meal, to identify potential traits for improvement; (2) Potential changes to OSR through genetic modification (GM) to improve seed quality; (3) Review of UK databases to quantify available levels of variation in the key traits; (4) A feed formulation exercise carried out to assess the value of a hypothetical new rape seed (and meal derived from it) based on an ‘improved’ genotype of Brassica napus.

While there is a wealth of information on anti-nutritional factors (ANFs) in the literature, e.g. fibre, glucosinolates (GSL) phytate, polyphenols, sinapine and tannins, it is difficult to quantify the financial benefits in terms of improvements to animal feed quality of reducing any ANF, other than GSL or fibre in OSR. Moreover, it is concluded that the traits improved by GM routes e.g. low phytate/high phytase and low sinapine, would be of little financial value, as there are technical solutions to addressing these ANFs already employed by the feed industry. Nevertheless, it is possible to envisage an improved rape seed genotype which, as well as low GSL, would have a thinner seed coat with resulting higher oil and protein and less fibre, having a real value in the feed market. Moreover, if such a genotype was also derived from yellow seed types, it would be possible to also reduce polyphenols in the seed coat, which would improve the attractiveness of rape seed and meal as feed ingredients and thereby increase their uptake. In general, the datasets studied contained information on oil, protein and GSL concentrations, and in some, seed yield, but lacked information on other ANF and relevant seed quality traits.

The value of an improved variety containing an additional 4% oil + protein (93%DM basis) with a thinner, yellow-seed coat was evaluated using a least cost ration formulation system for broilers, layers and pigs. For whole seed, improved seed types would be favoured in broiler diets where feed is pelleted and hence disruption of the seed coat and cotyledon occurs. The new (improved) meal appears to have the highest value in pig rather than poultry feeds. Within the poultry sector, the improved rape meal would appear to warrant a higher value in layer diets than broiler. To relate these improvements to a value to the industry, broadly speaking the improved feeding values are worth an extra £22.50/t to £30/t of rape seed, with the value of conventional rapeseed estimated at £345/t at the time of writing the report. This value could easily be eroded if the financial scenarios changed by lower prices of competing commodities, higher transport and/or energy costs, but support a general target of breeding for oil plus protein. Areas for further research are highlighted, particularly the need to evaluate the newer yellow seeded types of B. napus recently developed in Canada and France, to confirm performance in UK feeding systems.