Effects of protected nutrients on fatty acid composition in feedlot cattle.

Abstract

4A Effects of protected nutrients on fatty acid composition in feedlot cattle J.J. Davis1, R. Tume2, P. Allingham3 and G. Har per3 Cattle and Beef Quality Cooperative Research Centre 1 Agriculture Victoria, Rutherglen Vic 3685 2 Food Science Australia, Tingalpa Qld 4173 3 CSIRO Livestock Industries, Indooroopilly Qld 4068 jenny.davis@nre.vic.gov.au The amount and fatty acid composition of lipids significantly affects quality of any feedstuff. In beef, fatty acid composition affects shelf life, palatability, and nutritive value. An earlier study at the AV_Rutherglen Research Feedlot showed that a dietary supplement of nutrients protected from degradation in the rumen (Marble PlusTM; a combination of starch, protein and lipid) in a feedlot ration increased both visual (marble score) and chemically measured intramuscular fat (IMF) of Murray Grey steers. Cattle fed Marble PlusTM had higher proportions of C18 (di_ and tri_) unsaturated fatty acids (C18:2; C18:3) than did control cattle and this led to a decrease in the melting point (mp) of the subcutaneous fat to below 25oC. In the current study 60 F1 Wagyu and 60 Angus steers were fed a control or protected nutrient (Marble PlusTM) ration for 159 to 179 days. The performance and carcase data and the fatty acid compositions of the subcutaneous fat are shown in the Table 1. Marbling in control and treated steers was similar, suggesting either that nutrients were less protected in the later than in the earlier study, or that other factors outside the experimental design contributed this outcome. Genetic differences between animals in potential to marble could certainly contribute to differential response to treatment. The F1 Wagyu steers had higher (P<0.05) levels of marbling than did the Angus steers. There were also significant differences in the relative proportions of 14:0, 16:1, 18:0 and 18:2 fatty acids between the breeds: F1 Wagyu had lower proportions of C18:0 and higher proportions of mono_ unsaturates (C16:1; C18:1) suggesting different activity of the 9_desaturase enzyme compared with Angus. The observation that cattle fed Marble PlusTM had higher proportions of C18 (di_ and tri_) unsaturated fatty acids (C18:2; C18:3) than the control cattle, suggests that the fatty acids in the ration were indeed protected from rumen degradation and hence appeared in the subcutaneous fat. Table 1 Growth and fat deposition by steers given supplementar y nutrients protected from ruminal degradation. Control Initial LW, kg ADG, kg/d HSCW, kg P8 fat,mm DP% IMF% Marble score 14:0 16:0 16:1 18:0 18:1 18:2 18:3 MP, C a Treated 454 1.18 367 21 55.4 10.96 2.78 2.89 25.14 3.60 11.35 47.91 2.75 0.71 34.5 SED 5.0 0.04 3.9 1.2 0.29 0.61 0.14 0.12 0.44 0.24 0.67 0.59 0.07 0.02 1.7 P 0.901 0.074 0.254 0.318 0.833 0.197 0.239 0.841 0.023 0.047 0.570 0.979 <0.001 <0.001 0.426 Angus 425 1.24 360 19 55.4 9.74 2.55 2.73 25.25 3.35 12.15 48.09 2.18 0.52 38.1 Wagyu 481 1.04 369 21 55.5 11.30 2.84 3.00 25.97 4.26 10.30 47.76 1.93 0.50 33.9 SED 4.5 0.04 3.9 1.1 0.24 0.61 0.12 0.11 0.38 0.24 0.67 0.59 0.07 0.02 1.7 P <0.001 <0.001 0.014 0.117 0.491 0.011 0.017 0.014 0.058 <0.001 0.006 0.578 <0.001 0.346 0.013 452 1.11 362 20 55.5 10.08 2.61 2.85 26.08 4.01 11.10 47.95 1.37 0.31 36.6 a o Fatty acids are repor ted as percentages of total fatty acids Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)