Linseed supplementation of dairy cows : Effects on performances, methane emissions, milk composition and dairy products

Abstract

Supplementation of the dairy cow diet with linseed products is developing, aiming at increasing milk nutritional quality and decrea-sing methane output. Feedstuffs rich in polyunsatured fatty acids (FA) (especially linolenic acid) are used to complement diets poor in these FA, to produce a milk lower in saturated FA and with a lower linoleic/linolenic ratio. Linseed is indeed rich in linolenic acid. Greenhouse gas mitigation (including methane) is also a concern for the animal sector. Many studies involving linseed supplementation (with various processing treatments) have been published, and now enable to draw some conclusions about its effects. This article focuses on the supply of linseed and the various processing treatments. The effects of linseed on milk production, the composition of milk and dairy products, methane production and reproduction are reviewed. The results on milk production and composition are based on 41 published trials. Linseed cultivation is of little importance in France. Linseed in France is mainly supplied from European countries and Canada. Linseed varieties have different levels of linolenic acid. Dietary supplementation of cows with linseed slightly decreases dry matter intake, without significant effects on milk production. Milk saturated FA content is decreased and milk C18:1-trans are increased, especially with unprotected supplements (oil, extruded seeds). The C18:2 n-6 content is generally unchanged (except with oils) and starch-rich diets(for trans FA). The proportion of C18:3 n-3 is multiplied by 2 to 3 with the most effective treatments (seeds, flour), and can reach 1.4% of milk FA, with this type of supplement. The amount of lipid added does not significantly affect the milk content in C18:2 n-6 and C18:3 n-3, while it does for the C18:1-trans. Butter and cheeses have the same FA composition as the milk used for their production. The organoleptic properties of butters and cheeses are not affected by linseed addition. Different effects are reported in the literature to explain a potential increase in fertility, which remains to be confirmed. Dietary linseed supplementation decreases the production of methane. In conclusion, dietary linseed supplementation of dairy cows has the same effects as those with the addition of grass in the diet, except for a higher content of trans FA.