Effects of Implanting Beef Steers with Zeranol on Fatty Acid Composition of Subcutaneous and Intramuscular Fat1

The effect of implanting with zeranol on modulation of fatty acid composition, including omega-3 and omega-6 fatty acids, of subcutaneous (s.c.) and i.m. fat of steers was investigated, and carcasses were evaluated for quality grade and yield grade components. Forty steers were divided into 2 groups (20 steers/group); both groups were fed the same diet. Steers were fed to a constant 10 mm fat thickness (measured by ultrasound). Implanting had no effect (P > 0.05) on quality or yield grade components, but the concentration of polyunsaturated fatty acids (PUFA), including n-3 and n-6 fatty acids, was greater (P < 0.05) in the s.c. fat of implanted vs. non-implanted steers. Concentration of the saturated fatty acids (SFA) was less (P < 0.05) in the s.c. fat of implanted steers than in the s.c. fat of non-implanted steers. However, the amount of monounsaturated fatty acids was greater (P < 0.05) in the s.c. fat of non-implanted steers than in the s.c. fat of implanted steers. In the i.m. fat of implanted steers, the content of PUFA, including n-3 and n-6 fatty acids, and the amount of one monounsaturated fatty acid were greater (P < 0.05) than in the i.m. fat of non-implanted steers. The concentration of SFA was less (P < 0.05) in the i.m. fat of implanted vs. non-implanted steers. Implantation with zeranol caused an increase in the unsaturated:saturated fatty acid ratio and an increase in n-3:n-6 PUFA ratio. These results indicated that zeranol had no effect on carcass quality, but it had a positive effect in changing the fatty acid composition of the s.c. and the i.m. fat of steers from the saturated to unsaturated.