Background and Methodology
Noci et al (2005) have adequately referenced that lipids of ruminant origin are among the richest sources of Conjugated Linoleic Acid (CLA). The production of CLA occurs in the rumen as a result of incomplete biohydrogenation of dietary fatty acids. Ruminal biohydrogenation of predominant fatty acids (C18:3n-3) in pasture leads to the production of C18:trans-11 and ultimately CLA in tissue. The objective of this study was to determine the effect of time spent at pasture before slaughter on fatty acid composition of muscle fat and s.c. adipose tissue (SAT) of beef cattle. Sixty cross-bred Charolais heifers were assigned randomly to one of four dietary treatments. Fatty acid content of slaughtered animals was analyzed by gas chromatography.
Findings
Duration of grazing showed a quadratic tendency on mean carcass weight (P=0.08), but did not affect growth (P=0.27) or lipid content (P=0.13) of longissimus muscle (LM). Increasing the duration of grazing led to a linear increase (P<0.001) in the concentration of CLA in muscle fat and increased the concentration of C18:1trans-11 in both muscle fat fractions (P<0.001) and in SAT (P<0.001). The study concluded that muscle fat and SAT fatty acid profile was improved from human health perspective by pasture feeding and that this improvement depended on the duration of grazing.
Reference:
Noci, F., Monahan, F. J., French, P. & Moloney, A. P. (2005). The fatty acid composition of muscle fat and subcutaneous adipose tissue of pasture-fed beef heifers: influence of the duration of grazing. J. Anim. Sci. 83:1167-1178.