Effect of grazing fresh legumes or feeding silage on enzymes involved in the synthesis of milk fat in dairy cows

Summary

The impact of fresh legume types or silage on the composition of milk fatty acids and transcription of enzymes involved in the synthesis of milk fat in cows was studied. Three groups of cows grazed white clover, red clover and lucerne, respectively. A fourth group of cows was fed maize/grass silage. The cows grazing high proportions of legumes produced significantly more C18:1 trans-11, C18:2 cis9-trans11, C18:2 trans10-cis12 and C18:3 fatty acids than cows fed silage. White clover and lucerne grazing resulted in significantly less output of C18:1 trans9 in milk than red clover grazing and maize/grass silages. The transcription of Stearoyl-CoA desaturase (SCD) in mammary tissue was significantly increased by grassing high proportions legume whereas fatty acid synthase and Acetyl-Coa carboxylase was not affected by type of feeding. Furthermore, average milk fat globule diameter was correlated to daily milk fat yield but was not affected by feeding. Although the fresh forage affected the transcription of SCD in mammary tissue, the largest effects were on the trans11-based fatty acids, concluding that type of forage, i.e. fresh or silage, had larger impact on rumen fermentation pattern than on transcription of enzymes involved in the synthesis of milk fat.