Abstract
With increased demand for soybean meal to feed poultry and livestock, feeding diets with lower crude protein can reduce expense and lower nitrogen waste. Thus, the major objective of this study was to determine the effect of feeding a low crude protein (CP) soybean diet, and one in LCP soybean meal was replaced with Sprirullina platensis microalgae protein on antioxidant redox systems in liver and muscle tissue. Ross 708 male broilers were reared in floor pens and provided access to feed and water ad libitum. From day 1 - 14, all birds were provided a standard commercial corn soy-based starter diet. From d 15 - 37, the birds were divided into three groups (5 pens per diet; 12 birds/pen) and provided either: 1) A standard corn/soybean meal diet (21% CP, 3250 kcal/kg) (Control, CON), 2) a 17% negative control with lower crude protein (17%) (LCP) diet, and 3) the LCP diet in which Spirulina platensis meal was used to replace half of the soybean meal (LCP+AL). At the end of the study, 2 birds per pen (10 birds total per treatment) were randomly selected and humanely euthanized, after which liver and breast muscle samples were obtained and flash frozen in liquid nitrogen. The tissues were analyzed for antioxidant mRNA expression, antioxidant enzyme activity, and levels of reduced and oxidized glutathione (GSH and GSSG, respectively). In the liver, mRNA expression of 7 of 8 antioxidant enzymes analyzed were elevated (P<0.05) in the LCP+AL group compared to CON mRNA expression. However, activities of these enzymes were higher in the CON compared to the LCP+AL group. Both mRNA and enzyme activity values were intermediate for compared to the CON and LCP-AL groups. Hepatic concentrations of GSH, GSSG and thiobarbituric reactive substance were lower in the LCP group compared to CON and LCP+AL groups. In breast muscle, tissue mRNA expression of gamma glutamyl cysteine lyase , and superoxide dismutase 2 were lower (P<0.05), while GSH peroxidase 3 , GSH Reductase , thioredoxin, and GSH levels were higher (P< 0.05) in the LCP+AL compared to CON. Both GSH and GSSG levels were elevated in the LCP+AL group. The results of this study appear to paint a picture of increased antioxidant mRNA expression but decreased enzyme activity in the liver of the LCP+AL group compared to CON. Interestingly, reduced GSH levels in the LCP+AL group in breast muscle were twice as high as the CON and LCP groups indicating that the microalgae protein could provide considerable protection against thiolation of proteins and other structures in the cell.