Effects of dietary fish silage and fish fat on performance and egg quality of laying hens

A total of 45 laying hens were fed a control diet, or one of four diets containing 50 g kg(-1) fish silage and different levels of fish fat (1.8, 8.8, 16.8 or 24.8 g kg(-1)), to determine the effect of fish silage and fish fat in the diet on performance and egg quality. Fish silage did not affect feed intake, egg production, fatty acid composition of yolk, yolk color or sensory quality of eggs, compared with the control. The diets with 16.8 or 24.8 g kg(-1) fish fat decreased feed intake (P <0.001), egg production (P <0.001), and hen-day egg production (P <0.04), and increased yolk color index (P <0.003). The proportions of the fatty acid C22:1 (P <0.001), and PUFA as the sum of C18:2 n-6, C20:5 n-3, C22:5 n-3 and C22:6 n-3 (P <0.02) in egg yolk were highest for the fish silage diets with 24.8, 16.8 or 8.8 g kg(-1) fish fat, and lowest for the diet with 1.8 g kg-1 fish fat. Proportions of C18:1 (P <0.001) and C20:1 (P <0.001) were lowest for the diets with 16.8 or 24.8 g kg-1 fish fat. Egg yolk cholesterol did not differ among treatments. The diet with 16.8 g kg(-1) fish fat resulted in a more intense egg albumen whiteness as measured by the sensory study, compared with the other diets (P <0.05). There was a linear relationship between dietary fish fat level and increased off-taste intensity of egg yolk (P <0.03).