Effects of winter stocker growth rate and finishing system on: III. Tissue proximate, fatty acid, vitamin, and cholesterol content

Angus-cross steers (n = 198; 270 kg of BW; 8 mo) were used in a 3-yr study to assess the effects of winter stocker growth rate and finishing system on LM proximate, fatty acid, cholesterol, vitamin, and mineral composition. During the winter months (December to April), steers were randomly allotted to 3 stocker growth rates: low (0.23 kg/d), medium (0.45 kg/d), or high (0.68 kg/d). At the completion of the stockering phase, steers were allotted randomly within each stocker growth rate to a high concentrate (CONC) or pasture (PAST) finishing system and finished to an equal time endpoint. Winter stocker growth rate did not alter (P > 0.05) proximate, cholesterol, or vitamin content of the LM. All interactions among winter stocker growth rate and finishing system were nonsignificant, indicating that supplementation systems during winter stocker period did not influence beef composition after finishing on PAST or CONC. Finishing steers on CONC decreased (P < 0.001) moisture content of the LM and increased (P < 0.001) lipid content of the LM. Protein, ash, and cholesterol content of the LM did not differ (P > 0.05) between finishing systems. α-Tocopherol and β-carotene content of the LM were 288 and 54% greater, respectively, for PAST-finished cattle than CONC. B-vitamins, thiamine and riboflavin, were also present in greater (P = 0.001) concentrations for PAST than CONC. Calcium, Mg, and K contents of the LM were greater (P < 0.05) for PAST than CONC. Total fatty acid content of the LM was 49% less for PAST than CONC. Myristoleic, palmitoleic, and oleic acid concentrations were all less (P = 0.001) for PAST than CONC. Trans-10 octadecenoic acid percentage in LM was 97% greater (P = 0.001) for CONC than PAST; conversely, trans-11 vaccenic acid percentage in the LM was 90% greater (P = 0.001) for PAST than CONC. Conjugated linoleic acid, cis-9, trans-11 isomer, percentage was greater (P = 0.001) by 117% for PAST than CONC. Linoleic acid (C18:2) concentration did not differ (P > 0.05) among PAST and CONC. Concentrations of all n-3 fatty acids (linolenic acid, eicosapentaenoic, docosapentaenoic, docosahexaenoic) were greater (P = 0.01) for PAST than CONC. Total n-6 PUFA percentages were unchanged (P > 0.05) among finishing systems. The ratio of n-6 to n-3 fatty acids was 4.84 for CONC and 1.65 for PAST. Beef from CONC finished has a greater total, saturated, and monounsaturated fat content; in contrast, beef from PAST finished has less total, saturated, and monounsaturated fat content with greater contents of n-3 fatty acids and a decreased n-6 to n-3 ratio. Beef from PAST finished also has greater contents of B-vitamins and antioxidants (vitamin E and β-carotene).