Effect of grazing white clover pasture on milk composition of Holstein and Jersey cows

Summary in the original language of the document

Abstract: Because of its high saturated fatty acid (FA) content milk fat is considered hypercholesterolemic (Ulbricht and Southgate, 1991). Intake of unsaturated FA (UFA) reduces the plasma cholesterol concentrations (Fernandez and West, 2005). Especially conjugated linoleic acids (CLA) have shown positive effects on cardiovascular diseases (Valeille et al., 2004), prevention of cancer (Ip et al., 1994) and obesity (Park et al., 1997).
The aim of our project was to investigate how grazing could enhance the content of these beneficiary FA in milk from Holstein and Jersey cows. For both types of cow races we observed no direct effect of increased grazing in the diet on the short chain FA (SCFA) content in milk, implying that the de novo synthesis of these FA remained unaffected. Regarding the content of CLA c9,t11 there was a strong positive effect on Holstein milk (R2 = 0.88), but almost none on Jersey milk when the percentage of grazing increases in the diet, thus suggesting that the mammary gland 9-desaturase activities of these two cow races react differently to increasing pasture grazing.