Peanut cake is a by-product of biodiesel and contains relatively elevated lipid content. The inclusion of vegetable lipid sources in the diets can cause changes to the animal’s fatty acid profile. This study was conducted to determine the effect of substituting soybean meal with peanut cake in the feeding of goats on meat fatty acid profile. Forty goats were assigned at a completely random design, to 1 of 4 diets. The concentrate was composed of corn bran, soybean meal, and mineral premix; soybean meal was substituted with peanut cake at substitution rates of 0.0, 33.33, 66.67, and 100%. Tifton-85 (Cynodon sp.) hay, was used at 50% of TMR. After 62 d of feeding, the animals were slaughtered. The left loin of each animal was collected and subjected to lipid extraction, methylation, and the quantification of the fatty acid esters were obtained through gas chromatography analysis. A general linear model was used to perform linear and quadratic regression with 5% significance. The sum of fatty acid and atherogenicity index was not influenced by the substitution of soybean meal with peanut cake (Table 1). Peanuts possess an elevated content of oleic acid (C18:1) compared with soy, which is rich in linoleic acid (C18:2). However, it is important to consider that these ingredients compose, at most, 21% of the total diet, so their lipid characteristics were diluted by the other ingredients. Another important factor is the ruminal biohydrogenation, which tends to convert oleic, linoleic and linolenic acids into stearic acid (C18:0). The peanut cake can replace completely the soybean meal in goat diet with no effect on fatty acid profile of the meat. Table 1. Sum of fatty acids as the percentage of total fatty acids and atherogenicity index in the loin of goats fed diets with soybean meal substituted with peanut cake

Item	Amount of substitution (%DM)				SEM	P-value
0.0	33.3	66.6	100.0	Lin	Quad
Σ Saturated	53.41	58.28	55.4	56.55	1.25	0.29	0.17
Σ Unsaturated	46.59	41.72	44.6	43.45	1.25	0.29	0.17
Σ Polyunsaturated	3.36	3.75	3.09	3.53	0.45	0.96	0.97
Unsaturated: Saturated	0.87	0.72	0.81	0.77	0.04	0.22	0.16
n-6:n-3	15.89	14.81	15.47	19.52	2.86	0.13	0.18
Atherogenicity index	0.89	1.00	0.91	0.97	0.06	0.59	0.73