Rumen and milk fatty acid pattern when feeding forages from intensively managed or semi-natural grasslands
Lourenço, M.; Vlaeminck, B.; Bruinenberg, M.H.; Demeyer, D.; Fievez, V.
Communications in Agricultural and Applied Biological Sciences 69(2): 179-182
2004
ISSN/ISBN: 1379-1176 PMID: 15560216 Document Number: 569703
This study was conducted to evaluate the effect of replacing intensive forage by semi-natural grassland products on milk fatty acid composition, and to examine where these differences could be linked in the changes in rumen fat metabolism. Four lactating and rumen cannulated Holstein cows were assigned to a 4x4 Latin square design. Four different diets were used: diet 1 (100 IM), intensively managed (IM) silage; diet 2 (20 SPP), 80% IM silage and 20% species poor silage (SPP); diet 3 (60 SPP), 40% IM silage and 60% SPP silage and diet 4 (60 SPR), 40% IM silage and 60% species rich silage (SRP). The dietary supply of C18:3 n-3 mainly originated from the silages, whereas both silages and concentrate provided C18:2 n-6. Despite the reduced dietary supply of C18:3 n-3 by 60 SPP and 60 SPR, differences in milk C18:3 n-3 were small. The recovery of this fatty acid in milk was highest (7.63%) when cows were fed with 60 SPP. In 60 SPR diet, milk and rumen observations were in accordance, but rumen C18:3 n-3 concentrations were significantly higher than the expected value from the dietary C18:3 n-3 supply. Milk CLA c9, t11 concentrations were slightly higher in 60 SPP diet and almost double for 60 SPR diet. CLA was mainly produced in the mammary glands from C18:1 t11 through the activity of the desaturase enzyme and only a marginal part was directly from ruminal origin. The replacement of grass silage from intensively managed semi-natural grasslands suggests potentially reduced lipolysis and hydrogenation of C18:3 n-3, leading to a higher accumulation of intermediates in the rumen and inducing a higher supply to the mammary gland. Therefore, milk CLA concentrations are higher and dietary C18:3 n-3 is more efficiently secreted in the milk.