The effect of dietary rapeseed on milk protein fractions in dairy cows

Abstract

Significant interest exists on the inclusion of oilseeds in dairy cows' diets to improve the polyunsaturated fatty acid (PUFA) profile of their milk due to PUFA’s effects on human health. However, this strategy can affect milk protein fractions, compounds that play an important role in the dairy industry, and also affect consumers' health. The present work thus aimed to investigate the effect of rapeseed in dairy cows' diets on milk protein fractions such as caseins [s1-casein (s1-CN), s2-casein (s2-CN), β-casein (β-CN), k-casein (k-CN)], whey proteins [β-lactoglobulin (β-Lg), -lactalbumin (-La)], and minor proteins [lactoferrin (LF), bovine serum albumin (BSA), immunoglobulin G (IgG)]. The animals were randomly distributed in two groups, each fed with a control diet and a rapeseed-based diet, respectively. The protein fractions were determined using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Results indicated that the inclusion of rapeseed in dairy cows’ diets led to a significant decrease in total milk protein (from 3.73 ± 0.03 to 3.58 ± 0.03%, p < 0.05) and total casein content (from 2.96 ± 0.03 to 2.80 ± 0.03%, p < 0.05). Additionally, a significant decrease was also observed in the content of k-CN (from 32275 to 25883 A.U., p = 0.015), an important protein involved during milk coagulation; and a decrease tendency for β-CN also occurred (from 44746 to 41441 A.U., p = 0.087), the high content of which is associated with some human diseases. Dietary rapeseed also decreased the β-Lg content (from 61256 to 52694 A.U., p = 0.016), which is positively correlated with cheese quality. Other minor protein fractions such as BSA and IgG were also decreased by the rapeseed diet.