Lipoprotein Patterns in Normal Lactating Holstein Cows Bled at Various Times: Effects of Milking

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Abstract
Six lactating Holstein cows (60-90 days) fed normal rations were bled via jugular catheters at 1130 (pre-milking), 1300 (post-milking), 1900, 2330 (pre-milking), 0100 (post-milking) and 0700 h. Serum lipoproteins were isolated and fractionated by gel chromatography into 3 major fractions: very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL). VLDL protein content was high at both pre-milking times but decreased following milking. HDL protein showed an inverse relationship to that of VLDL with peak HDL protein concentrations occurring after both milking times. Although no other dependent variables exhibited statistically significant time effects, mean VLDL triglyceride concentrations declined after each milking time. Results suggested an increased rate of VLDL catabolism following milking.