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

Author
item Duckett, Susan
item Neel, James - Jim
item Fontenot, Joseph
item Clapham, William

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2009
Publication Date: 6/5/2009
Citation: Duckett, S.K., Neel, J.P., Fontenot, J.P., Clapham, W.M. 2009. Effects of winter stocker growth rate and finishing system on: III. tissue proximate, fatty acid, vitamin, and cholesterol content. Journal of Animal Science. 87(9):2961-2970.

Interpretive Summary: Consumer markets for natural, forage-finished beef products are expanding in the U.S. As a result of this demand, some beef producers are starting to finish cattle on forages and direct market this grass-fed beef to consumers. Animal performance prior to finishing can be highly variable and the impact of this variability on beef nutritional profile is largely unknown. Agricultural Marketing Service has established a voluntary standard for a grass (forage) fed marketing claim for ruminant livestock and producers can now request a grass fed claim be verified by USDA. A simple test would be useful to verify grass fed beef and differentiate product produced by conventional versus grass-fed systems. The objective of this research was to evaluate the effect of stocker growth rate and finishing system on beef nutritional characteristics. Winter stocker growth rate did not alter beef loin muscle nutritional profile. Total fat, and fatty acids associated with increased human blood cholesterol were lower for pasture than grain-fed. Beef from pasture-finished animals has a higher content of omega-3 fatty acids, and also a lower, more desirable omega-6 to omega-3 ratio. Pasture-finished beef also has higher levels of B-vitamins and antioxidants. The unique omega-6 to omega-3 fatty acid ratio levels in pasture-finished product gives the single best measure to potentially verify finishing method (conventional Vs grass finishing) in beef samples. Since winter rate of gain did not impact beef nutritional profile, animal performance prior to finishing can very greatly without altering beef nutritional quality.

Technical Abstract: Angus-cross steers (n = 198; 270 kg; 8 mo) were used in a three-year 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 three stocker growth rates: low (0.23 kg/d; LOW), medium (0.45 kg/d; MED), or high (0.68 kg/d; HIGH). At the completion of the stockering phase, steers were allotted randomly within each stocker growth rate to either 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 non-significant indicating that supplementation systems during winter stocker period did not influence beef composition after finishing on PAST or CONC. Finishing steers on CONC lowered (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) among finishing systems. a-Tocopherol and beta-carotene content of the LM were 288% and 54% higher, respectively, for PAST finished than CONC. B-vitamins, thiamin and riboflavin, were also present in higher (P = 0.001) concentrations for PAST than CONC. Calcium, Mg and K contents of the LM were higher (P < 0.05) for PAST than CONC. Total fatty acid content of the LM was 49% lower for PAST than CONC. Myristoleic, palmitoleic and oleic acid concentrations were all lower (P = 0.001) for PAST than CONC. Trans-10 octadecenoic acid percentage in LM was 97% higher (P = 0.001) for CONC than PAST; conversely, trans-11 vaccenic acid (TVA) percentage in the LM was 90% higher (P = 0.001) for PAST than CONC. Conjugated linoleic acid, cis-9 trans-11 isomer, percentage was higher (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, EPA, DPA, DHA) were higher (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 higher total, saturated and monounsaturated fat content; in contrast, beef from PAST finished has lower total, saturated and monounsaturated fat content with higher contents of n-3 fatty acids and a lower n-6 to n-3 ratio. Beef from PAST finished also has greater contents of B-vitamins and antioxidants (vitamin E and beta-carotene).