Short communication: A decrease in diameter of milk fat globules accompanies milk fat depression induced by conjugated linoleic acid supplementation in lactating dairy cows

摘要

Milk fat is secreted from the mammary gland in theform of milk fat globules (MFG). Although milk fatdepression has been studied since the beginning of thelast century, the extent to which this phenomenon altersMFG synthesis is not fully understood. The aimof this study was to evaluate the effect of conjugatedlinoleic acid (CLA) on the size and distribution of MFGduring milk fat depression in dairy cows. Twelve Holsteincows in mid lactation (145 ± 31 d in milk, 583 ±34.6 kg of body weight, and 27.2 ± 2.4 kg of milk/d)were randomly assigned to a control diet or control plusCa-protected CLA at 15 g/kg of dry matter for a 6-dperiod. The average diameter and particle size distributionof MFG were measured using a Mastersizer 3000laser particle size analyzer (Malvern Instruments Ltd.,Malvern, UK). Feeding CLA did not affect dry matterintake (16.2 ± 0.4 kg/d), milk production (28.4 ± 0.4kg/d), milk protein, or lactose, but it decreased milkfat content (3.46 vs. 2.52%). In addition, surface arearelatedmean diameter of fat globules in cows fed CLAwas lower compared with controls (3.02 vs. 3.45 μm).The percentage of large fat globules decreased and thatof small fat globules increased in response to CLA.Overall, the data suggest that the milk fat depressioninduced by CLA is accompanied by a decrease in averagediameter of MFG.