Herbe et qualités nutritionnelles et organoleptiques des produits laitiers

The nature of the forages consumed by dairy cows has a large effect on both the nutritional and the organoleptic characteristics of the dairy products. This paper summarises the results found in the corresponding literature. Compared to grazed grass, diets based on maize silage or concentrates give rise to milks low in vitamins A and E, in beta-carotene, in unsaturated fatty acids, including linolenic acid and the conjugates of linoleic acid. but high in saturated fatty acids. Besides, maize silage gives cheeses and butters with a whiter colour and a firmer consistence, which are generally less appreciated by the tasters. The effects of grass are all the more important as it is utilized at an earlier stage, and they are influenced by the method of conservation and by the botanical composition. Important differences among the organoleptic and nutritional characteristics are also observed in the dairy products when the cows are fed a diet based on conserved grass, or when they are left to graze in spring. As compared to hay, grass silage, when properly made, influences but little, or not at all, the organoleptic qualities of the cheeses, were it not for their colour, which is yellower with silage, because of the higher beta-carotene content of the silage. Milks from silage-fed cows are also richer in vitamin E, but less rich in linolenic acid. Several recent trials have evidenced an effect of the floristic makeup of the forages ingested by dairy cows on the texture and the flavour and savour of the cheeses. Moreover, when the cows graze a floristically diversified sward, the milks and the cheeses are poorer in beta-carotene, but richer in linolenic acid and the conjugates of linoleic acid, a fact supposedly due to the secondary metabolites present in certain plant species acting on the bio-hydrogenation in the rumen.

Comparativement à l’herbe pâturée, les rations à base d’ensilage de maïs ou de concentrés sont à l’origine de laits pauvres en vitamine a et e, en ß-carotène, en acides gras insaturés incluant l’acide alpha-linolénique et les isomères conjugués de l’acide linoléique, mais riches en acides gras saturés. l’ensilage de maïs conduit par ailleurs à des fromages ou des beurres plus blancs et plus fermes, généralement moins appréciés. les effets de l’herbe sur les caractéristiques organoleptiques et nutritionnelles des produits laitiers sont d’autant plus importants qu’elle est utilisée à un stade précoce et ils varient selon son mode de conservation (pâturée, ensilée, fanée...) et sa nature botanique. ces différents effets sont détaillés dans le texte.