Effect of feeding rumen-protected dietary protein–oil supplements on fatty acid composition and α-tocopherol content of blood serum and muscle lipids of lambs

Abstract

This study evaluated the effect of feeding a rumen-protected, protein–oil supplement (RDPS) containing α-tocopheryl acetate (TA) and sunflower oil on fatty acid composition and α-tocopherol concentrations of blood serum and muscle in lambs. The RDPS contained 32.0% CP and 32.2% fat on a DM basis, and 465 IU Vitamin E/kg. Twenty-four, cross-bred lambs were allotted into three treatment groups with two pens of four lambs per group. Each pen of four lambs was fed one of three dietary treatments for 10 weeks: (1) control diet, 5.12 kg DM of corn basal diet (BD), 1.50 kg DM of grass hay, and 40 g of molasses as-fed basis, (2) Vitamin E diet, TA (1000 IU) plus control diet, or (3) RDPS diet, 2.0 kg as-fed basis of RDPS plus control diet (3.12 kg of DM of BD). Blood samples were collected biweekly from individual lambs over the 10-week feeding trial; longissimus dorsi (LD) and psoas major (PM) muscles were obtained from each lamb carcass to analyze α-tocopherol and fatty acid composition. Compared with lambs fed the control or Vitamin E diet, lambs fed the RDPS had a higher ( P < 0.05) concentration of linoleic (C18:2 n6) acid (23.04% or 24.93% versus 33.5%) and lower ( P < 0.05) concentrations of palmitic (C16:0) and oleic (C18:1 n9) acids in blood serum lipids. However, no differences ( P > 0.05) were found in concentrations of C16:0, C18:1 n9 or C18:2 n6 in the serum lipids from lambs fed the control and Vitamin E diets. Furthermore, the RDPS diet substantially increased ( P < 0.05) C18:2 n6 levels in LD and PM muscle lipids but decreased ( P < 0.05) C16:0 and C18:1 n9 compared to the control or Vitamin E diet. Lambs fed Vitamin E or RDPS diet had higher ( P < 0.05) concentrations of serum α-tocopherol than lambs fed the control diet, whereas serum α-tocopherol content in lambs fed the RDPS was 28.7% higher ( P < 0.05) than lambs fed the Vitamin E. Consequently, lambs fed the RDPS had higher ( P < 0.05) α-tocopherol concentrations in PM (7.43 μg/g) muscle than lambs fed the Vitamin E; however, no significant differences ( P > 0.05) were found in α-tocopherol concentrations in LD muscle from lambs fed either Vitamin E or RDPS diet. Results indicated that the RDPS protected polyunsaturated fat and α-tocopheryl acetate from ruminal degradation, resulting in increased content in blood serum and deposition in muscle tissues of lambs.